[Federal Register Volume 62, Number 138 (Friday, July 18, 1997)]
[Rules and Regulations]
[Pages 38856-38896]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-18580]



[[Page 38855]]

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Part V





Environmental Protection Agency





_______________________________________________________________________



40 CFR Part 50



National Ambient Air Quality Standards for Ozone; Final Rule

  Federal Register / Vol. 62, No. 138, Friday, July 18, 1997 / Rules 
and Regulations  

[[Page 38856]]



ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 50

[ADA-95-58; FRL-5725-3]
RIN-2060-AE57


National Ambient Air Quality Standards for Ozone

AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.

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SUMMARY: This document describes EPA's decision to revise the national 
ambient air quality standards (NAAQS) for ozone (O3) based 
on its review of the available scientific evidence linking exposures to 
ambient O3 to adverse health and welfare effects at levels 
allowed by the current O3 standards. The current 1-hour 
primary standard is replaced by an 8-hour standard at a level of 0.08 
parts per million (ppm) with a form based on the 3-year average of the 
annual fourth-highest daily maximum 8-hour average O3 
concentrations measured at each monitor within an area. The new primary 
standard will provide increased protection to the public, especially 
children and other at-risk populations, against a wide range of 
O3-induced health effects, including decreased lung 
function, primarily in children active outdoors; increased respiratory 
symptoms, particularly in highly sensitive individuals; hospital 
admissions and emergency room visits for respiratory causes, among 
children and adults with pre-existing respiratory disease such as 
asthma; inflammation of the lung, and possible long-term damage to the 
lungs. The current 1-hour secondary standard is replaced by an 8-hour 
standard identical to the new primary standard. The new secondary 
standard will provide increased protection to the public welfare 
against O3-induced effects on vegetation, such as 
agricultural crop loss, damage to forests and ecosystems, and visible 
foliar injury to sensitive species.
EFFECTIVE DATE: This rule is effective September 16, 1997.
ADDRESSES: A docket containing information relating to the EPA's review 
of the O3 primary and secondary standards (Docket No. A-95-
58) is available for public inspection in the Central Docket Section of 
the U.S. Environmental Protection Agency, South Conference Center, Room 
4, 401 M St., SW., Washington, DC. This docket incorporates the docket 
from the previous review of the O3 standards (Docket No. A-
92-17) and the docket established for the air quality criteria document 
(Docket No. ECAO-CD-92-0786). The docket may be inspected between 8 
a.m. and 3 p.m. on weekdays, and a reasonable fee may be charged for 
copying. The information in the docket constitutes the complete basis 
for the decision announced in this final rule. For the availability of 
related information, see ``SUPPLEMENTARY INFORMATION.''
FOR FURTHER INFORMATION CONTACT: David McKee, MD-15, Air Quality 
Standards and Strategies Division, Office of Air Quality Planning and 
Standards, U.S. Environmental Protection Agency, Research Triangle 
Park, NC 27711; telephone: (919) 541-5288; e-mail: 
[email protected].
SUPPLEMENTARY INFORMATION:

Availability of Related Information

    Certain documents are available from the U.S. Department of 
Commerce, National Technical Information Service, 5285 Port Royal Road, 
Springfield, VA 22161. Available documents include:
    (1) Air Quality Criteria for O3 and Other Photochemical 
Oxidants (``Criteria Document'') (three volumes, EPA/600/P-93-004aF 
through EPA/600/P-93-004cF, July 1996, NTIS # PB-96-185574, $169.50 
paper copy, $58.00 microfiche).
    (2) The Review of the National Ambient Air Quality Standards for 
O3: Assessment of Scientific and Technical Information 
(``Staff Paper'')(EPA-452/R-96-007, June 1996, NTIS # PB-96-203435, 
$67.00 paper copy and $21.50 microfiche). (Add a $3.00 handling charge 
per order.)
    A limited number of copies of other documents generated in 
connection with this standard review, such as documents pertaining to 
human exposure and health risk assessments, and vegetation exposure, 
risk, and benefits analyses can be obtained from: U.S. Environmental 
Protection Agency Library (MD-35), Research Triangle Park, NC 27711, 
telephone (919) 541-2777. These and other related documents are also 
available for inspection and copying in the EPA docket identified under 
``ADDRESSES''.

Electronic Availability

    The Staff Paper and human exposure and health risk assessment 
support documents are now available on the Agency's Office of Air 
Quality Planning and Standards (OAQPS) Technology Transfer Network 
(TTN) Bulletin Board System (BBS) in the Clean Air Act Amendments area, 
under Title I, Policy/Guidance Documents. To access the bulletin board, 
a modem and communications software are necessary. To dial up, set your 
communications software to 8 data bits, no parity and one stop bit. 
Dial (919) 541-5742 and follow the on-screen instructions to register 
for access. After registering, proceed to choice `` Gateway to TTN 
Technical Areas'', then choose `` CAAA BBS''. From the main menu, 
choose ``<1> Title I: Attain/Maint of NAAQS'', then `` Policy 
Guidance Documents.'' To access these documents through the World Wide 
Web, click on ``TTN BBSWeb'', then proceed to the Gateway to TTN 
Technical areas, as above. If assistance is needed in accessing the 
system, call the help desk at (919) 541-5384 in Research Triangle Park, 
NC.

Implementation Strategy for Revised Air Quality Standards

    On Wednesday, July 16, 1997, President Clinton signed a memorandum 
to the Administrator specifying his goals for the implementation of the 
O3 and PM standards. Attached to the President's memorandum 
is a strategy prepared by an interagency Administration group outlining 
the next steps that would be necessary for implementing these 
standards. The EPA will prepare guidance and proposed rules consistent 
with the President's memorandum. Copies of the Presidential document 
are available in paper copy by contacting the U.S. Environmental 
Protection Agency Library at the address under ``Availability of 
Related Information'' and in electronic form as discussed above in 
``Electronic Availability.''
    The following topics are discussed in this preamble:
I. Background
    A. Legislative Requirements
    B. Related Control Requirements
    C. Review of Air Quality Criteria and Standards for 
O3
    D. Summary of Proposed Revisions to the O3 Standards
II. Rationale for the Primary O3 Standard
    A. Introduction
    B. Elements of the Primary Standard
    C. Communication of Public Health Information
III. Rationale for the Secondary O3 Standard
    A. Introduction
    B. Need for Revision of Current Secondary Standard
    C. Final Decision on the Secondary Standard
IV. Other Issues
    A. Cost Considerations
    B. Margin of Safety
    C. Comment Period
    D. 1990 Act Amendments
V. Technical Changes to Part 50
VI. Revisions to Appendices D, E, and H
VII. Regulatory and Environmental Impact Analyses

[[Page 38857]]

    A. Executive Order 12866
    B. Regulatory Flexibility Analysis
    C. Impact of Reporting Requirements
    D. Unfunded Mandates Reform Act
    E. Environmental Justice
    F. Submission to Congress and Comptroller General
VIII. Response to Petition for Administrator Browner's Recusal
IX. References

I. Background

A. Legislative Requirements

    Two sections of the Act govern the establishment, review, and 
revision of NAAQS. Section 108 (42 U.S.C. 7408) directs the 
Administrator to identify certain pollutants which ``may reasonably be 
anticipated to endanger public health or welfare'' and to issue air 
quality criteria for them. These air quality criteria are to 
``accurately reflect the latest scientific knowledge useful in 
indicating the kind and extent of all identifiable effects on public 
health or welfare which may be expected from the presence of [a] 
pollutant in the ambient air ***.''
    Section 109 (42 U.S.C. 7409) directs the Administrator to propose 
and promulgate ``primary'' and ``secondary'' NAAQS for pollutants 
identified under section 108. Section 109(b)(1) defines a primary 
standard as one ``the attainment and maintenance of which in the 
judgment of the Administrator, based on [the] criteria and allowing an 
adequate margin of safety, are requisite to protect the public 
health.'' The margin of safety requirement was intended to address 
uncertainties associated with inconclusive scientific and technical 
information available at the time of standard setting, as well as to 
provide a reasonable degree of protection against hazards that research 
has not yet identified. Both kinds of uncertainties are components of 
the risk associated with pollution at levels below those at which human 
health effects can be said to occur with reasonable scientific 
certainty. Thus, by selecting primary standards that provide an 
adequate margin of safety, the Administrator is seeking not only to 
prevent pollution levels that have been demonstrated to be harmful but 
also to prevent lower pollutant levels that she finds may pose an 
unacceptable risk of harm, even if the risk is not precisely identified 
as to nature or degree. The Act does not require the Administrator to 
establish a primary NAAQS at a zero-risk level but rather at a level 
that reduces risk sufficiently so as to protect public health with an 
adequate margin of safety. The selection of any particular approach to 
providing an adequate margin of safety is a policy choice left 
specifically to the Administrator's judgment. Lead Industries 
Association v. EPA. (647 F.2d 1130, 1161-62 (D.C. Cir. 1980)).
    A secondary standard, as defined in section 109(b)(2), must 
``specify a level of air quality the attainment and maintenance of 
which in the judgment of the Administrator, based on [the] criteria, 
[are] requisite to protect the public welfare from any known or 
anticipated adverse effects associated with the presence of [the] 
pollutant in the ambient air.'' Welfare effects as defined in section 
302(h) (42 U.S.C. 7602(h)) include, but are not limited to, ``effects 
on soils, water, crops, vegetation, manmade materials, animals, 
wildlife, weather, visibility, and climate, damage to and deterioration 
of property, and hazards to transportation, as well as effects on 
economic values and on personal comfort and well-being.''
    Section 109(d)(1) of the Act requires periodic review and, if 
appropriate, revision of existing air quality criteria and NAAQS. 
Section 109(d)(2) requires appointment of an independent scientific 
review committee to review criteria and standards and recommend new 
standards or revisions of existing criteria and standards, as 
appropriate. The committee established under section 109(d)(2) is known 
as the Clean Air Scientific Advisory Committee (CASAC), a standing 
committee of EPA's Science Advisory Board.

B. Related Control Requirements

    States are primarily responsible for ensuring attainment and 
maintenance of ambient air quality standards once EPA has established 
them. Under section 110 of the Act (42 U.S.C. 7410) and related 
provisions, States are to submit, for EPA approval, State 
implementation plans (SIP's) that provide for the attainment and 
maintenance of such standards through control programs directed to 
sources of the pollutants involved. The States, in conjunction with 
EPA, also administer the prevention of significant deterioration 
programs (42 U.S.C. 7470-7479) for these pollutants. In addition, 
Federal programs provide for nationwide reductions in emissions of 
these and other air pollutants under Title II of the Act (42 U.S.C. 
7521-7574), which involves controls for automobile, truck, bus, 
motorcycle, nonroad engine, and aircraft emissions; the new source 
performance standards under section 111 (42 U.S.C. 7411); and the 
national emission standards for hazardous air pollutants under section 
112 (42 U.S.C. 7412).

C. Review of Air Quality Criteria and Standards for O3

    The last review of O3 air quality criteria and standards 
was completed in March 1993 with notice of a final decision not to 
revise the existing primary and secondary standards (58 FR 13008). The 
current primary and secondary standards are each set at a level of 0.12 
ppm, with a 1-hour averaging time and a 1-expected-exceedance form, 
such that the standards are attained when the expected number of days 
per calendar year with maximum hourly average concentrations above 0.12 
ppm is equal to or less than 1, averaged over 3 years (as determined by 
40 CFR part 50, Appendix H).1
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    1 A more complete history of the O3 NAAQS is 
presented in section II.B. of the Office of Air Quality Planning and 
Standards Staff Paper, Review of National Ambient Air Quality 
Standards for O3: Assessment of Scientific and Technical 
Information (U.S. EPA, 1996b).
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    The EPA initiated this current review of the air quality criteria 
and standards in August 1992 with the development of a revised Air 
Quality Criteria Document for O3 and Other Photochemical 
Oxidants, henceforth the ``Criteria Document.'' Several workshops were 
held by EPA's National Center for Environmental Assessment (NCEA) to 
discuss health and welfare effects information during the summer and 
fall of 1993. An external review draft of the Criteria Document made 
available to the public and to the CASAC in the spring of 1994 was 
reviewed at a public CASAC meeting held on July 20-21, 1994. Based on 
comments made at the meeting, NCEA staff prepared a second external 
review draft, which was reviewed at a public CASAC meeting on March 21-
22, 1995. At the same meeting, the CASAC also reviewed draft portions 
of a staff paper prepared by the OAQPS, Review of National Ambient Air 
Quality Standards for O3: Assessment of Scientific and 
Technical Information (henceforth, the ``Staff Paper''), focusing on 
health effects and the primary NAAQS.2 Taking into account 
CASAC and public comments, staff revised both documents and made new 
drafts available for public and CASAC review during the summer of 1995. 
The OAQPS staff also prepared and made available draft portions of the 
Staff Paper focusing on welfare effects and the secondary standard.
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    2 The Staff Paper evaluates policy implications of the key 
studies and scientific information in the Criteria Document, 
identifies critical elements that EPA staff believes should be 
considered, and presents staff conclusions and recommendations of 
suggested options for the Administrator's consideration.

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[[Page 38858]]

    A public CASAC meeting was held on September 19-20, 1995, at which 
time CASAC came to closure in its review of the draft Criteria Document 
and the primary standard sections of the draft Staff Paper. In a 
November 28, 1995 letter from the CASAC chair to the Administrator, 
CASAC advised that the final draft Criteria Document ``provides an 
adequate review of the available scientific data and relevant studies 
of O3 and related photochemical oxidants'' (Wolff, 1995a). 
Further, in a November 30, 1995 letter, CASAC advised the Administrator 
that the primary standard portion of the draft Staff Paper ``provides 
an adequate scientific basis for making regulatory decisions concerning 
a primary O3 standard'' (Wolff, 1995b). The final Criteria 
Document (U.S. EPA, 1996a) reflects CASAC and public comments received 
at and subsequent to the September 1995 CASAC meeting.
    Based on comments on the Staff Paper from the September 1995 CASAC 
meeting, revisions were made to the secondary standard sections of the 
Staff Paper, which were reviewed at a public CASAC meeting held on 
March 21, 1996. At that meeting and in a subsequent letter to the 
Administrator, CASAC concluded that the secondary standard sections of 
the draft Staff Paper ``provide an appropriate scientific basis for 
making regulatory decisions concerning a secondary O3 
standard'' (Wolff, 1996). The final Staff Paper (U.S. EPA, 1996b) 
reflects CASAC and public comments received at and subsequent to the 
September 1995 and March 1996 meetings on the primary standard and 
secondary standard sections, respectively.
    On November 27, 1996 EPA announced its proposed decision to revise 
the NAAQS for O3 (61 FR 65716, December 13, 1996, 
hereinafter ``proposal'') as well as its proposed decision to revise 
the NAAQS for particulate matter (PM). In the proposal, EPA identified 
proposed revisions, based on the air quality criteria for 
O3, and solicited public comments on alternative primary and 
secondary standards and on the proposed forms of the standards.
    To ensure the broadest possible public input on the O3 
and PM proposals, EPA took extensive and unprecedented steps to 
facilitate the public comment process beyond the normal process of 
providing an opportunity to request a hearing and receiving written 
comments submitted to the rulemaking docket. The EPA established a 
national toll-free telephone hotline to facilitate public comments on 
the proposed revisions to the O3 and PM NAAQS, and on 
related notices dealing with the implementation of revised 
O3 and PM standards, as well as a system for the public to 
submit comments on the proposals electronically via the Internet. Over 
14,000 calls and over 4,000 electronic mail messages were received 
through these channels. The public could also access key supporting 
documents (including the Criteria Document, Staff Paper, related 
technical documents and fact sheets) via the Internet.
    The EPA also held several public hearings and meetings across the 
country to provide direct opportunities for public comment on the 
proposed revisions to the O3 and PM NAAQS and to disseminate 
information to the public about the proposed standard revisions. On 
January 14 and 15, 1997, EPA held concurrent, 2-day public hearings in 
Boston, MA, Chicago, IL, and Salt Lake City, UT. A fourth public 
hearing, which focused primarily on PM monitoring issues, was held in 
Durham, NC on January 14, 1997. Over 400 citizens and organizations 
testified during these public hearings. EPA also held two national 
satellite telecasts to answer questions on the standards and 
participated in meetings sponsored by the Air and Waste Management 
Association on the proposed revisions to the standards at more than 10 
locations across the country. Beyond that, several EPA regional offices 
held public meetings and workshops and participated in hearings that 
States and cities held around the country.
    As a result of this intensive effort to solicit public input, over 
50,000 written and verbal comments were received on the proposed 
revisions to the O3 NAAQS by the close of the public comment 
period on March 12, 1997. The major issues raised in the comments are 
discussed throughout the preamble of this final rule. A comprehensive 
summary of all significant comments, along with EPA's response to such 
comments (hereafter ``Response to Comments''), can be found in the 
docket for this rulemaking (Docket No. A-95-58).
    The focus of this current review of the air quality criteria and 
standards for O3 and related photochemical oxidants is on 
public health and welfare effects associated with exposure to ambient 
levels of tropospheric O3. Tropospheric O3 is 
chemically identical to stratospheric O3, which is produced 
miles above the earth's surface and provides a protective shield from 
excess ultraviolet radiation. In contrast, tropospheric O3 
at sufficient concentrations has been associated with harmful effects 
due to its oxidative properties and its presence in the air that people 
and plants take up during respiratory processes. Ozone is not emitted 
directly from mobile or stationary sources but, like other 
photochemical oxidants, commonly exists in the ambient air as an 
atmospheric transformation product. Ozone formation is the result of 
chemical reactions of volatile organic compounds (VOC), nitrogen oxides 
(NOx), and oxygen in the presence of sunlight and generally 
at elevated temperatures. A detailed discussion of atmospheric 
formation, ambient concentrations, and health and welfare effects 
associated with exposure to O3 can be found in the Criteria 
Document and in the Staff Paper.

D. Summary of Proposed Revisions to the O3 Standards

    For reasons discussed in the proposal, the Administrator proposed 
to replace the current 1-hour primary standard for O3 with 
an 8-hour standard set at 0.08 ppm, which would be met at an ambient 
air quality monitoring site when the 3-year average of the annual 
third-highest daily maximum 8-hour average O3 concentration 
is less than or equal to 0.08 ppm. The proposal solicited comments on 
alternative 8-hour standards set at 0.09 ppm, which generally 
represents the continuation of the present level of protection, and 
0.07 ppm, which would be highly precautionary in nature, as well as on 
retaining the current primary standard. The proposal also solicited 
comments on alternative forms of the standard, specific data handling 
and rounding conventions used in determining attainment with the 
standard, and issues related to the communication of public health 
information.
    With regard to the secondary standard, the Administrator proposed 
to replace the current 1-hour secondary standard with one of two 
alternative standards: either one set identical to the proposed primary 
standard or a new seasonal standard expressed as a sum of hourly 
O3 concentrations greater than or equal to 0.06 ppm, 
cumulated over 12 hours per day during the consecutive 3-month period 
of maximum concentrations during the O3 monitoring season, 
set at a level of 25 ppm-hour. The proposal solicited comments on these 
two alternatives, as well as on specific issues related to the form of 
a seasonal standard and on an enhanced rural air quality monitoring 
network.

[[Page 38859]]

II. Rationale for the Primary Standard

A. Introduction

    1. Overview . This notice presents the Administrator's final 
decision regarding the need to revise the current primary O3 
standard, and, more specifically, regarding the averaging time, level, 
and form of a new primary standard to replace the current 1-hour 
standard. This decision is based on a thorough review, in the Criteria 
Document, of the scientific information on human health effects 
associated with exposure to ambient levels of O3, including 
evaluation of key studies published through 1995. This decision also 
takes into account:
    (1) Staff Paper assessments of the most policy-relevant information 
in the Criteria Document and analyses of human exposure and risk, 
presented in the Staff Paper and supporting technical reports.
    (2) CASAC advice and recommendations, as reflected in discussions 
of drafts of the Criteria Document and Staff Paper at public meetings, 
in separate written comments, and in CASAC's letters to the 
Administrator.
    (3) Public comments received during the development of these 
documents, either in connection with CASAC meetings or separately.
    (4) Extensive public comments received on the proposal regarding 
the primary O3 standard.
    After taking this information and comments into account and for the 
reasons discussed below in this unit, the Administrator concludes that 
revisions to the current primary standard to provide increased public 
health protection are appropriate at this time to protect public health 
with an adequate margin of safety. Further, the Administrator 
determines that it is appropriate to establish a revised 8-hour, 0.08 
ppm primary standard with a form based on the 3-year average of the 
annual fourth-highest daily maximum 8-hour average O3 
concentrations measured at each monitor within an area.
    As discussed more fully below in this unit, the rationale for the 
final decision regarding the O3 primary NAAQS includes 
consideration of:
    (1) Health effects information to inform judgments as to the 
likelihood that exposures to ambient O3 result in adverse 
health effects for exposed individuals.
    (2) Insights gained from human exposure and risk assessments to 
provide a broader perspective for judgments about protecting public 
health from the risks associated with O3 exposure.
    (3) Specific conclusions with regard to the elements of a standard 
(i.e., averaging time, level, and form) that, taken together, would be 
appropriate to protect public health with an adequate margin of safety.
    (4) Alternative views of the significance of the effects and 
factors to be considered in policy judgments about the appropriate 
elements of the standard.
    The health effects information and human exposure and risk 
assessments were summarized in the proposal and are only briefly 
outlined below. More fully discussed in the following units of this 
preamble is the Administrator's rationale, in light of key issues 
raised in public comments, for concluding that it is appropriate to 
revise the specific elements of the current standard including 
averaging time (Unit II.B.1.), level (Unit II.B.2.), and form (Unit 
II.B.3.). Finally, the related subject of the communication of public 
health information, and the public comments received on this subject, 
are summarized in Unit II.C.
    2. Health effects information. The last review of the air quality 
criteria for O3 included an evaluation of key studies 
published through early 1989 and was the basis for EPA's 1993 decision 
not to revise the primary standard at that time. However, in 
recognition of the large number of new studies, particularly on 6- to 
8-hour exposures to O3, that had become available since 
early 1989 but had not undergone rigorous assessment and review by 
CASAC, the EPA made clear in the 1993 final decision notice that it 
would proceed with the next review as rapidly as possible to consider 
this new information. Thus, the current review of health effects 
information focused on a large body of information published since 1989 
that would lead to a more informed decision than was possible in 1993 
as to whether an O3 primary standard with a longer averaging 
time was appropriate to protect public health.
    The proposal reviewed the human health effects associated with 
exposure to ambient levels of O3 based on an integrative 
assessment of human clinical, epidemiological, and animal toxicological 
studies available through 1995, as assessed in the Criteria Document 
and Staff Paper. Based on this information, an array of health effects 
has been attributed to short-term (1 to 3 hours), prolonged (6 to 8 
hours), and long-term (months to years) exposures to O3.
    Acute health effects3 are induced by short-term 
exposures to O3 (observed at concentrations as low as 0.12 
ppm), generally while individuals are engaged in moderate or heavy 
exertion, and by prolonged exposures to O3 (observed at 
concentrations as low as 0.08 ppm), typically while individuals are 
engaged in moderate exertion. Moderate exertion levels are more 
frequently experienced by individuals than heavy exertion levels. The 
acute health effects include transient pulmonary function responses, 
transient respiratory symptoms, effects on exercise performance, 
increased airway responsiveness, increased susceptibility to 
respiratory infection, increased hospital admissions and emergency room 
visits, and transient pulmonary inflammation. Based in particular on 
new information available since the last review of the air quality 
criteria for O3 was completed, such acute health effects 
have been observed following prolonged exposures at moderate levels of 
exertion at concentrations of O3 as low as 0.08 ppm. Groups 
at increased risk of experiencing such effects include active children 
and outdoor workers who regularly engage in outdoor activities and 
individuals with preexisting respiratory disease (e.g., asthma, chronic 
obstructive lung disease). Further, it is recognized that some 
individuals are unusually responsive to O3 and may 
experience much greater functional and symptomatic effects from 
exposure to O3 than the average individual.
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    3 ``Acute health effects'' of O3 are defined as those 
effects induced by short-term and prolonged exposures to 
O3. Examples of these effects are functional, 
symptomatic, biochemical, and physiologic changes.
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     With regard to chronic health effects4, the collective 
data from studies of laboratory animals and human populations have many 
ambiguities, but provide suggestive evidence of such effects in humans. 
It is clear from toxicological data that O3-induced lung 
injury is roughly similar across species (including monkeys, rats, and 
mice) with responses that are concentration dependent. The currently 
available information provides at least a biologically plausible basis 
for considering the possibility that repeated inflammation associated 
with exposure to O3 over a lifetime may result in sufficient 
damage to respiratory tissue such that individuals later in life may 
experience a reduced quality of life,

[[Page 38860]]

although such relationships remain highly uncertain.
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    4 ``Chronic health effects'' of O3 are defined as 
those effects induced by long-term exposures to O2. 
Examples of these effects are structural damage to lung tissue and 
accelerated decline in baseline lung function.
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    EPA's consideration of this health effects information necessarily 
included judgments with respect to when these physiological effects 
become so significant that they should be regarded as adverse to the 
health of individuals experiencing the effects. In making these 
judgments, the Administrator looked to guidelines published by the 
American Thoracic Society (1985) and the advice of CASAC. The proposal 
summarized the criteria and reasoning for EPA's judgments on this 
issue, upon which the CASAC panel expressed a consensus view that these 
``criteria for the determination of an adverse physiological response 
was reasonable'' (Wolff, 1995b). The criteria take into account the 
degree of severity of the effects; the likelihood that the effects 
would interfere with normal activity for individuals with impaired 
respiratory systems or active healthy individuals; the likelihood that 
the effects would result in additional or more frequent use of 
medication, medical treatment, or emergency room visits for individuals 
with impaired respiratory systems; and the implications of single or 
repeated occurrences of the effects for an individual.
    Some commenters raised concerns regarding the criteria used by EPA 
to make determinations as to when effects become adverse, citing 
CASAC's closure letter (Wolff, 1995b) stating that ``there was 
considerable concern that the criteria for grading physiological and 
clinical responses to O3 was confusing if not misleading.'' 
These concerns with the draft criteria were discussed at length during 
a public CASAC meeting, resulting in very specific agreements as to how 
to revise the draft criteria so as to be consistent with CASAC's advice 
(Transcript of CASAC meeting, September 19-20, 1995, pp. 242-248). 
Having reached such specific agreement, CASAC advised that further 
review of the final version of these criteria, subsequently 
incorporated in both the final Criteria Document and Staff Paper, was 
unnecessary.
    Other commenters have questioned whether judgments made in this 
review are consistent with those made in the last review with regard to 
when physiological and clinical effects become adverse to individuals 
experiencing such effects. Specifically, the commenters focused on the 
judgment stated in the 1993 final decision notice (58 FR 13008, March 
9, 1993) that ``lesser effects associated with [1- to 3-hour] exposure 
to O3 in the range of 0.12 ppm to 0.15 ppm observed in the 
controlled human studies did not constitute adverse effects for 
purposes of section 109 of the Act.'' The ``lesser effects'' referred 
to in that notice involved responses of a maximum decrease in lung 
function [as measured by forced expiratory volume in 1 second 
(FEV1)] of from 9 percent to 16 percent for the most 
sensitive individuals exposed in this range, with few, if any, 
symptoms. The EPA notes that this judgment is, in fact, consistent with 
judgments presented in the 1996 proposal, which identify moderate and 
large lung function decrements (as reflected in EPA's risk assessment 
by FEV1 decreases of  15 percent and  
20 percent, respectively, with the most sensitive individuals 
experiencing FEV1 decreases as large as 40 percent to 50 
percent at 6- to 8-hour exposures in the range of 0.08 ppm to 0.10 ppm 
in controlled human studies), and moderate to severe symptoms as being 
adverse.
    3. Exposure and risk assessments. To put judgments about health 
effects that are adverse for individuals into a broader public health 
context, EPA conducted quantitative assessments to estimate 
O3 exposures and related risks for the general population 
and two at-risk groups, ``outdoor children'' and ``outdoor workers,'' 
living in nine representative U.S. urban areas. This broader context 
included consideration, to the extent possible, of the size of the 
particular population groups identified as at risk for various effects, 
the estimated number of people within at-risk groups likely to 
experience O3-related adverse effects, the estimated number 
of occurrences of such effects, and the estimated number of people who 
would experience exposures of concern5 associated with 
various air quality scenarios representing attainment of the current 
and alternative 8-hour standards. Consideration was also given to the 
kind and degree of uncertainties inherent in assessing such exposures 
and risks. Such considerations provided a basis for judgments discussed 
in the proposal about the levels of exposure and risk associated with 
the current and alternative standards, which helped inform judgments 
about the adequacy of public health protection afforded by the current 
and alternative standards.
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    5 ``Exposures of concern'' refer throughout to exposures at and 
above 0.08 ppm, 8-hour average, at which a range of health effects 
have been observed in controlled human studies, but for which data 
were too limited to allow for quantitative risk assessment.
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    Risk estimates were developed for those effects for which 
sufficient concentration-response information was available from 
studies evaluated in the Criteria Document, including adverse lung 
function and respiratory symptom responses. In a separate analysis, 
excess respiratory hospital admissions for individuals with asthma 
associated with attainment of alternative standards were also 
estimated, using a risk model for this health endpoint based on the 
results of an epidemiological study in New York City (Thurston et al., 
1992) for which adequate air quality information was available to 
assess population risk6. These quantitative risk estimates 
(for that subset of O3-related effects for which information 
is sufficient to conduct such quantitative analyses) add to our 
understanding of the broader array of health effects that are 
associated with exposure to O3 but for which quantitative 
risk estimates could not be developed.
---------------------------------------------------------------------------

    6 This study is one of several studies, mainly conducted in the 
northeastern portion of the United States and southeastern Canada, 
reporting excess daily respiratory-related hospital admissions 
associated with elevated O3 levels within the general 
population and, more specifically, for individuals with asthma.
---------------------------------------------------------------------------

    The methodology, results, and key observations from these 
assessments were presented in the proposal. The EPA believes, and CASAC 
concurred, that the models selected to estimate exposure and risk were 
appropriate and that the methods used to conduct the health risk 
assessment for adverse lung function and respiratory symptom responses 
represent the state of the art. Nevertheless, the Administrator and 
CASAC recognized that there are many uncertainties inherent in such 
analyses, and that not all uncertainties inherent in such analyses 
could be quantified and reflected in ranges of risk estimates (Wolff, 
1995b), as discussed in the proposal and the referenced technical 
support documents.
    The exposure and risk assessments available at the time of proposal 
had been conducted to evaluate the O3 exposures and risks 
associated with attainment of the current 1-hour standard and various 
alternative 8-hour standards under consideration early in the standards 
review process when the assessments were initiated. The EPA and CASAC 
recognized at that time that additional alternative standards might 
need to be analyzed later in the review process. Upon deciding to 
propose a standard with a concentration-based form in the Fall of 1996, 
EPA staff initiated supplemental analyses to estimate exposures and 
risks7 for the

[[Page 38861]]

specific standard to be proposed and alternative standards on which the 
proposal solicited comment. In conducting these supplemental analyses, 
several technical changes were made based on insights gained from the 
initial analyses.8 The supplemental assessment (Richmond, 
1997) was placed in the docket and on the TTN on February 12, 1997, and 
its availability was announced in the Federal Register notice extending 
the public comment period on the proposal, providing the public the 
opportunity to comment on the supplemental assessment (61 FR 7743, 
February 20, 1997).
---------------------------------------------------------------------------

    7 The analyses were conducted for the at-risk population of 
outdoor children, the group with the highest exposures and risks. 
Outdoor children are the subset of children between the ages of 6 
and 18 years old who tend to be active outdoors, and include 
approximately over 30 percent to 45 percent of all children in this 
age group in the nine urban areas analyzed.
    8 These changes primarily focused on the air quality data used 
in the exposure analysis and on the air quality adjustment 
procedures used to simulate ambient O3 concentrations 
upon attainment of alternative standards.
---------------------------------------------------------------------------

    Key observations and results from the initial and supplemental 
exposure and risk assessments that are most pertinent to the decision 
to revise the current primary standard are highlighted in the following 
unit, together with discussion of the key issues raised in public 
comments on the methodology and public health implications of these 
assessments.

B. Elements of the Primary Standard

    In selecting a primary standard for O3, the 
Administrator must specify: Averaging time, O3 concentration 
(i.e., level), and form (i.e., the air quality statistic to be used as 
a basis for determining compliance with the standard).9 All 
three of these elements are necessary to define a standard and to 
determine the degree of public health protection afforded by the 
standard. The proposal outlined the key factors considered in selecting 
each of these elements for the proposed standard, as well as the range 
of options for each element on which the EPA solicited comment. The 
factors reflect an integration of information on acute and chronic 
health effects associated with exposure to ambient O3; 
expert judgments on the adversity of such effects for individuals; and 
policy judgments, informed by air quality and exposure analyses and 
quantitative risk assessment when possible, as to the point at which 
risks would be reduced sufficiently to achieve protection of public 
health with an adequate margin of safety.
---------------------------------------------------------------------------

    9 This review focused only on a standard for O3, as 
the most appropriate surrogate for photochemical oxidants.
---------------------------------------------------------------------------

    This approach to selecting a primary standard was endorsed by CASAC 
(Wolff, 1995b), particularly through its advice to the Administrator 
that ``EPA's risk assessments must play a central role in identifying 
an appropriate level'' and its recognition that ``the selection of a 
specific level and [form] is a policy judgment.'' Further, it was the 
consensus view of CASAC that the ranges of 8-hour average levels (0.07 
to 0.09 ppm) and forms (concentration-based forms that generally allow 
for 1 to 5 exceedances) on which the proposal solicited comment were 
appropriate.
    The following discussion focuses primarily on those considerations 
that were most influential in the Administrator's final decisions on 
these elements, taking into account the comments received on the range 
of options identified in the proposal.
    1. Averaging time. In proposing to change the averaging time of the 
primary standard from 1 to 8 hours, the Administrator was concurring 
with the unanimous recommendation of CASAC (Wolff, 1995b) ``that the 
present 1-hour standard be eliminated and replaced with an 8-hour 
standard,'' and that more research is needed to resolve uncertainties 
about potential chronic effects before appropriate consideration can be 
given to establishing a long-term (e.g., seasonal or annual) primary 
standard. The Administrator's proposed decision was supported by the 
following key observations and conclusions:
    (1) The 1-hour averaging time specified in the current NAAQS was 
originally selected primarily on the basis of health effects associated 
with short-term (i.e., 1- to 3-hour) exposures, with qualitative 
consideration given to preliminary information on potential 
associations with longer exposure periods.
    (2) Substantial new health effects information available for 
consideration in this review demonstrates associations between a wide 
range of health effects and prolonged (i.e., 6- to 8-hour) exposures 
below the level of the current 1-hour NAAQS.
    (3) Results from the quantitative risk analyses show that attaining 
a standard with a 1-hour averaging time reduces the risk of 
experiencing health effects associated with both 1-hour and 8-hour 
exposures. Likewise, attaining an 8-hour standard reduces the risk of 
experiencing health effects associated with both 8-hour and 1-hour 
exposures. Thus, reductions in risks from both short-term and prolonged 
exposures can be achieved through a primary standard with an averaging 
time of either 1 or 8 hours. As a result, establishment of both 1-hour 
and 8-hour standards would not be necessary to reduce risks associated 
with the full range of observed acute health effects.
    (4) The 8-hour averaging time is more directly associated with 
health effects of concern at lower O3 concentrations than is 
the 1-hour averaging time. It was thus the consensus of CASAC ``that an 
8-hour standard was more appropriate for a human health-based standard 
than a 1-hour standard.'' (Wolff, 1995b)
    (5) While there is a large animal toxicology database providing 
clear evidence of associations between long-term (e.g., from several 
months to years) exposures and lung tissue damage, with additional 
evidence of reduced lung elasticity and accelerated loss of lung 
function, there is no corresponding evidence for humans. Moreover, the 
state of the science has not progressed sufficiently to permit 
quantitative extrapolation of the animal-study findings to humans. 
Thus, the Administrator concluded that consideration of a separate 
long-term primary O3 standard is not appropriate at this 
time. As discussed below, however, the Administrator considered the 
possibility of long-term effects in selecting the level of an 8-hour 
standard, which will provide protection against such effects to the 
extent they may occur in humans, by lowering overall air quality 
distributions and, thus, reducing cumulative long-term exposures.
    The public comments reflect broad support for a standard with an 8-
hour averaging time, either alone or in conjunction with a 1-hour 
standard. This support was typically based on references to:
    (1) Evidence of health effects from 6- to 8-hour exposures to 
O3 concentrations down to 0.08 ppm, which are lower than 
those concentrations that have induced such effects after 1- to 3-hour 
exposures, and which are lower than the 0.12 ppm level of the current 
standard.
    (2) Analyses indicating that an 8-hour standard would limit both 1- 
and 8-hour exposures.
    (3) CASAC's unanimous agreement that the current 1-hour standard 
should be replaced by an 8-hour standard. In considering the adequacy 
of the current 1-hour standard alone in light of the health effects 
evidence, some commenters have highlighted the statement in the 
Criteria Document that there is ``strong evidence that ambient 
exposures to O3 can cause significant exacerbations of 
preexisting respiratory disease in the general public at concentrations 
below 0.12 ppm.'' (U.S. EPA, 1996a, p. 7-171)
    Commenters expressing support for an 8-hour averaging time included 
not only those who supported a level of public health protection 
consistent with

[[Page 38862]]

or greater than that reflected by EPA's proposed standard, but also 
many who disagreed for various reasons with the need for increased 
public health protection beyond that provided by the current standard. 
Of those supporting an 8-hour averaging time but not supporting the 
need for increased protection, some expressed the view that the 
averaging time of a health-based standard should be consistent with the 
exposures of most concern, while others were simply neutral between the 
choices of retaining the current 1-hour standard and replacing it with 
an ``equivalent'' 8-hour standard.
    The EPA agrees with the considerations raised by those commenters 
who favor an 8-hour standard. Further, in considering the 
appropriateness of an 8-hour standard as compared to a 1-hour standard, 
EPA also notes the results of its exposure and risk assessments which 
show variability across the nine urban areas analyzed with regard to 
the extent to which the current 1-hour standard, and alternative 8-hour 
standards, limit 8-hour exposures of concern and associated risks of 
adverse health effects. As noted in the proposal and in the 
supplemental risk assessment, there is much greater variability across 
urban areas, particularly in looking at the seven current nonattainment 
areas examined, in the extent to which the current 1-hour standard 
limits such exposures of concern and risks than for the alternative 8-
hour standards. For example, the updated assessment estimates that the 
current 1-hour standard results in 8-hour exposures of concern at and 
above 0.08 ppm10 that vary by almost two orders of magnitude 
across these areas. In contrast, alternative 8-hour standards at the 
proposed level of 0.08 ppm result in estimated 8-hour exposures of 
concern and risks that are much more consistent.11 In EPA's 
view, the fact that an averaging time of 8 hours results in a 
significantly more uniformly protective national standard than the 
current 1-hour standard is an important public health policy 
consideration that supports the selection of an 8-hour averaging time.
---------------------------------------------------------------------------

    10 More precisely, exposures at and above 0.08 ppm refers to 
estimates of exposures to O3 concentrations  
0.081 ppm from the exposure assessment.
    11 In terms of the percent of outdoor children estimated to be 
exposed to O3 concentrations at and above 0.08 ppm while 
engaged in moderate exertion, the current 1-hour standard results in 
a range across the seven nonattainment areas of approximately 0.3 
percent to 24 percent of such children, whereas alternative 8-hour 
standards, at the proposed level of 0.08 ppm, result in a 
significantly more uniform degree of protection, with ranges of 
approximately 2 percent to 9 percent, third-highest concentration 
form, and 3 percent to 11 percent, fifth-highest concentration form, 
across the areas.
---------------------------------------------------------------------------

    Those commenters who did not support EPA's proposal for an 8-hour 
averaging time generally did not support any revision to the current 
standard. These commenters predominantly focused on two basic points: 
The generally improving trends in air quality under the current 
standard and associated air quality management programs, which, 
commenters argued, suggest that there is no need for EPA to adopt any 
more stringent standard; and observations made in CASAC's closure 
letter (Wolff, 1995b) with regard to EPA's risk assessment not 
demonstrating any ``bright line'' threshold of effects or acceptable 
risk. With regard to the first issue, EPA agrees that air quality 
trends are improving as a consequence of ongoing control programs 
designed to attain the current NAAQS. The EPA does not, however, 
believe that these trends relieve the Agency of its statutory mandate 
to review and, if appropriate, revise the NAAQS on the basis of the 
best available scientific evidence to establish standards that protect 
public health with an adequate margin of safety. The fact that current 
control programs are resulting in progress toward improving air quality 
does suggest that it is important to ensure that such progress is 
maintained during any transition to a revised standard.
    With regard to the second issue, commenters very frequently quoted 
from the CASAC closure letter (Wolff, 1995b) stating ``that there is no 
bright line' which distinguishes any of the proposed standards (either 
the level or the number of allowable exceedances) as being 
significantly more protective of public health'' and that ``the 
selection of a specific level and number of allowable exceedances is a 
policy judgment.'' These commenters have variously interpreted these 
statements as a CASAC consensus that the differences in the public 
health protection afforded by any of the alternative standards were too 
small to be important from a public health perspective, not 
statistically significantly different, or simply not different at all. 
Based on these interpretations, the commenters argued that it is not 
appropriate to revise the standard in any way, because a revised 
standard would result in disruption to ongoing programs, additional 
planning requirements, and increased implementation costs, but would 
provide no or only very little improvement in public health protection.
    The EPA believes that these commenters have misconstrued or too 
narrowly interpreted CASAC's advice to the Administrator by not 
considering the entire range of views and recommendations included in 
its closure letter. Specifically, CASAC began its summary of 
recommendations to the Administrator (Wolff, 1995b) by stating that 
``[t]he Panel was in unanimous agreement that the present 1-hour 
standard be eliminated and replaced with an 8-hour standard.'' This 
agreement was based on ``the consensus of the Panel that an 8-hour 
standard was more appropriate for a human health-based standard than a 
1-hour standard.'' Thus, CASAC was unequivocal in its advice to the 
Administrator with regard to which averaging time the health effects 
evidence more strongly supports. While some commenters have also quoted 
statements by individual Panel members at CASAC meetings suggesting 
that choosing between a 1- or 8-hour averaging time is a ``policy'' 
choice, these individual statements during the course of CASAC's review 
do not contradict nor supersede the clear and unanimous agreement of 
CASAC on averaging time as conveyed to the Administrator in its closure 
letter.
    In considering these comments, EPA also believes it is important to 
put into a public health perspective CASAC's observations about the 
differences among alternative standards in protecting the public from 
the health effects that were quantitatively estimated in EPA's risk 
assessment. In the closure letter (Wolff, 1995b), CASAC observed that 
``the differences in the percent of outdoor children *** responding 
between the present standard and the most stringent proposal *** are 
small and their ranges overlap for all health endpoints.'' Most 
importantly, EPA notes that the primary standard would provide 
protection from a broader array of health effects than it was possible 
to consider in its quantitative risk assessment. This perspective is 
clearly shared in particular by those CASAC panel members who 
personally favored a level or range of levels that included the 
proposed level of 0.08 ppm, in that the closure letter characterizes 
their views as reflecting, in part, their ``concern over the evidence 
for chronic deep lung inflammation from the controlled human and animal 
exposure studies.'' While the risk of this effect, as well as other 
effects related to 6- to 8-hour exposures in the Criteria Document and 
Staff Paper (including increased airway responsiveness, impairment of 
host

[[Page 38863]]

defenses suggesting an increased susceptibility to respiratory 
infection, and increased emergency room visits, doctor visits, and 
frequency of medication use by individuals with impaired respiratory 
systems) could not be quantitatively estimated in EPA's risk 
assessment, EPA believes that consideration of these effects is 
nevertheless important in making public health policy judgments.
    Further, in interpreting CASAC's statements on EPA's risk 
assessment report (Whitfield et al., 1996) that there is no ``bright 
line'' which distinguishes any of the standards as being 
``significantly'' more protective, and that the ``ranges overlap,'' EPA 
notes that there are statistically significant differences in the 
estimated risks for the standards analyzed with 1- and 5-exceedance 
forms. This information was presented to CASAC at its September 1995 
meeting (CASAC meeting transcript, September 19-20, 1995, pp. 108-109). 
Further, EPA again notes that whether one judges the differences to be 
significant or small can depend on whether one focuses on percentages, 
as CASAC's letter did, or on total numbers of times that children or 
other at-risk individuals experience such effects. The overlap in the 
ranges of risk referred to in the CASAC letter reflect differences 
among urban areas used in EPA's risk analysis (e.g., air quality, 
exposure patterns, environmental factors), not random uncertainties in 
risk estimates within any given urban area. Thus, the fact that the 
ranges overlap does not mean that there are no real or statistically 
significant differences in protection among alternative standards. To 
the extent that the quoted statements from CASAC's closure letter are 
read as implying that CASAC considered the differences not to be 
statistically significant (or that there are no differences at all in 
the protection afforded by the alternative standards), EPA disagrees 
with that reading.
    Another group of commenters, while supporting an 8-hour standard, 
specifically opposed replacing the current 1-hour standard with an 8-
hour standard, but favored instead both 8-hour and 1-hour standards. 
These commenters generally felt that a greater degree of public health 
protection than that provided by the proposed standard was warranted, 
and that standards based on both averaging times were necessary to 
provide the requisite protection from 1- and 8-hour exposures of 
concern. These commenters generally argued that an 8-hour standard 
alone could still allow for high 1-hour exposures of concern, or that 
the retention of the current 1-hour standard was critical to 
maintaining current pollution control measures. As an initial matter, 
EPA is delaying revocation of the 1-hour standard to ensure an 
effective transition to the 8-hour standard, as discussed in Unit 
II.B.4 of this preamble. While EPA agrees that it is possible that an 
8-hour standard alone could allow for high 1-hour exposures of concern, 
at and above 0.12 ppm,12 EPA's exposure assessments estimate 
that alternative 8-hour standards, at the proposed level of 0.08 ppm 
but with different forms, would be very effective in limiting 1-hour 
exposures, and generally even more effective in limiting 1-hour 
exposures of concern than is the current 1-hour standard. More 
specifically, the updated assessment estimates that upon attainment of 
alternative 8-hour, 0.08 ppm standards, with forms ranging up to the 
fifth-highest concentration form, less than 0.1 percent of outdoor 
children are likely to experience any 1-hour exposures greater than 
0.12 ppm while at heavy exertion levels in four to seven of the nine 
urban areas analyzed, whereas this is true for only two of the nine 
areas upon attainment of the current 1-hour standard. In all nine areas 
both the current and alternative 8-hour, 0.08 ppm standards are 
estimated to limit such exposures to less than 1 percent of the outdoor 
children. Thus, EPA concludes that an 8-hour averaging time does 
effectively limit both 1- and 8-hour exposures of concern.
---------------------------------------------------------------------------

    12 The EPA recognizes this possibility exists especially in the 
very few areas with unusually ``peaky'' air quality patterns (i.e., 
in which the ratio of the 1- and 8-hour average design values for 
the current and proposed standards is greater than 1.5).
---------------------------------------------------------------------------

    For the reasons discussed above in this unit, and after taking into 
account the range of views expressed in the public comments, the 
Administrator finds that replacing the current 1-hour standard with an 
8-hour standard, in combination with the decisions on level and form 
described below, is appropriate to provide adequate and more uniform 
protection of public health from both short-term (1 to 3 hours) and 
prolonged (6 to 8 hours) exposures to O3 in the ambient air.
    2. Level. Taken together, the level and form of the standard, for a 
given averaging time, determine the degree of public health protection 
afforded by the standard. Consideration of the level of the standard 
discussed in this unit of the preamble reflects a recognition of this 
linkage between level and form (discussed separately below in Unit 
II.B.3).
    The Administrator's decision to propose the level of an 8-hour 
primary O3 standard at 0.08 ppm, and to solicit comment on 
alternative levels, necessarily reflected a recognition, as emphasized 
by CASAC, that it is likely that ``O3 may elicit a continuum 
of biological responses down to background concentrations'' (Wolff, 
1995b). Thus, in the absence of any discernible threshold, it is not 
possible to select a level below which absolutely no effects are likely 
to occur. Nor does it seem possible, in the Administrator's judgment, 
to identify a level at which it can be concluded with confidence that 
no ``adverse'' effects are likely to occur. In such a case, as CASAC 
has advised, the traditional paradigm for standard-setting cannot be 
applied in the usual way, and assessments of risk ``must play a central 
role in identifying an appropriate level'' (Wolff, 1995b). Thus, the 
Administrator's task became one of attempting to select a standard 
level that would reduce risks sufficiently to protect public health 
with an adequate margin of safety, since a zero-risk standard is 
neither possible nor required by the Act. In this and other NAAQS 
reviews the CASAC has generally recognized that the selection of 
specific standards requires that the Administrator make public health 
policy judgments in addition to determinations of a strictly scientific 
nature. The Administrator's public health policy judgment on the level 
of the proposed standard was framed by the considerations discussed 
above in this unit and informed by the following key observations and 
conclusions:
    (1) During the last review of the O3 criteria and 
standards, CASAC concluded that the existing 1-hour standard set at 
0.12 ppm O3 provided ``little, if any, margin of safety,'' 
and that the upper end of the range of consideration for a 1-hour 
standard should be 0.12 ppm (McClellan, 1989). In addition, several 
members of the CASAC panel recommended that consideration should be 
given to a lower 1-hour level of 0.10 ppm to offer some protection 
against effects for which there was preliminary information at that 
time of associations with 8-hour exposures to O3.
    Regarding currently available evidence of O3-related 
effects:
    (2) Based on a significant body of information available since the 
last review, there is now clear evidence from human clinical studies 
that O3 effects of concern are associated with the 6- to 8-
hour exposures tested. Studies were done at 6- to 8-hour exposure 
levels of 0.12, 0.10, and 0.08 ppm. This includes evidence of the 
following statistically significant responses at 6- to 8-hour exposures 
to the lowest concentration evaluated, 0.08 ppm O3, at 
moderate

[[Page 38864]]

exertion: lung function decrements, respiratory symptoms (e.g., cough, 
pain on deep inspiration), nonspecific bronchial responsiveness, and 
biochemical indicators of pulmonary inflammation. Field studies provide 
evidence of similar functional and symptomatic effects at ambient 
O3 exposures that are consistent with the clinical findings. 
Laboratory animal studies provide supporting evidence of O3-
induced biochemical indicators of inflammation and functional changes.
    (3) Numerous epidemiological studies have reported excess hospital 
admissions and emergency department visits for respiratory causes (for 
asthmatic individuals and the general population) attributed primarily 
to ambient O3 exposures, including O3 
concentrations below the level of the current standard, with no 
discernible threshold at or below this level. The biological 
plausibility of attributing such effects to ambient O3 
exposures is supported by human studies showing increased nonspecific 
bronchial responsiveness, laboratory animal studies showing pulmonary 
changes that decrease the effectiveness of the lung's defenses against 
bacterial respiratory infections, and the reasonable anticipation that 
O3 exposures also increase the risk of respiratory 
infections in humans, based on the many similarities between animal and 
human defense mechanisms.
    (4) Long-term laboratory animal studies suggest that changes in 
lung biochemistry and structure may, under certain circumstances, 
become irreversible, although it is unclear whether long-term exposures 
to ambient O3 levels result in similar chronic health 
effects in humans.
    Regarding the types and severity of O3-induced 
physiological effects that are considered to be adverse to the health 
status of individuals experiencing such effects:
    (5) With regard to lung function decrements and respiratory 
symptoms, the Administrator recognized that these O3-induced 
effects are transient and reversible, and concluded that the extent to 
which such effects are adverse to the health status of an individual 
depends upon the severity, duration, and frequency with which an 
individual experiences such effects throughout the O3 
season. While group mean responses in clinical studies at the lowest 
exposure level tested of 0.08 ppm are typically small or mild in 
nature, responses of some sensitive individuals are sufficiently severe 
and extended in duration to be considered adverse. This would 
especially be true to the extent that those individuals likely to 
experience such effects would, on average, experience them several 
times a year.
    (6) With regard to increased hospital admissions and emergency room 
visits, the Administrator judged that such effects are clearly adverse 
to individuals.
    (7) With regard to pulmonary inflammation, the Administrator 
recognized that singular occurrences of inflammation are likely 
reversible and potentially of little health significance. On the other 
hand, based on laboratory animal studies, repeated inflammatory 
responses associated with exposure to O3 over a lifetime 
have the potential to result in damage to respiratory tissue such that 
individuals later in life may experience a reduced quality of life. 
Furthermore, there is the possibility that repeated pulmonary 
inflammatory responses could adversely affect asthmatic individuals by 
resulting in increased medication use, medical treatment, and/or 
emergency room visits and hospital admission. Such effects in 
asthmatics are of special concern particularly in light of the growing 
asthma problem in the United States and the increasing rates of asthma-
related mortality and hospitalizations, especially among children in 
general and black children in particular. While O3 has not 
been shown to cause asthma, the available evidence suggests that 
O3 may exacerbate asthma. Accordingly, the Administrator 
judged that repeated exposures to O3 levels that produce 
inflammation of the lungs are adverse to individuals likely to 
experience such exposures over long periods of time.
    The Administrator considered the results of the exposure and risk 
analyses and the following key observations and conclusions from these 
analyses in putting effects considered to be adverse to individuals 
into a broader public health perspective and in making judgments about 
the level of a standard that would reduce risk sufficiently to protect 
public health with an adequate margin of safety:
    (8) The median risk estimates for respiratory functional and 
symptomatic effects, as well as for excess hospital admissions of 
asthmatics for respiratory causes, are approximately the same or only 
marginally smaller for some of the 8-hour, 0.09 ppm standard options 
evaluated (including those with forms ranging from 1- to 3-expected-
exceedances13) as compared to the current 1-hour, 0.12 ppm 
NAAQS (risk estimates are somewhat larger for an 8-hour, 0.09 ppm, 5-
expected-exceedance standard as compared to those for the current 
NAAQS).
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    13 The upper end of this range, 3-expected-exceedances, was 
based on air quality comparisons, since risk estimates were only 
available at the time of proposal for the 1- and 5-expected-
exceedance forms of a 0.09 ppm standard. This range is consistent 
with the results of the updated risk assessment.
---------------------------------------------------------------------------

    (9) Within any given urban area, statistically significant 
reductions in exposure and risk associated with respiratory functional 
and symptomatic effects result from alternative 8-hour standards as the 
level changes from 0.09 ppm to 0.08 ppm to 0.07 ppm. These reductions 
represent differences of hundreds of thousands of times that children 
in the nine urban areas included in the analysis would likely 
experience such effects under the range of alternative standards 
considered relative to the current standard. There are significant 
uncertainties in such quantitative estimates, however, and there is no 
break point or bright line that differentiates between acceptable and 
unacceptable risks within this range.
    (10) Similarly, reductions in hospital admissions for respiratory 
causes for asthmatic individuals and the general population are 
estimated to occur with each change in the level of the standard from 
0.09 ppm to 0.08 ppm to 0.07 ppm. However, hospital admissions for 
asthmatic individuals associated with ambient O3 exposures 
within the range of standard levels under consideration represent a 
relatively small fraction of the total respiratory-related hospital 
admissions for asthmatics over the O3 season.
    (11) Estimated exposures to O3 concentrations at and 
above 0.08 ppm (at which increased nonspecific bronchial 
responsiveness, decreased pulmonary defense mechanisms, and indicators 
of pulmonary inflammation have been observed in humans) while engaged 
in moderate exertion are essentially zero at the 0.07 ppm standard 
level (with a 1-expected-exceedance form) for the seven nonattainment 
areas evaluated in the exposure analyses for the at-risk population of 
outdoor children. Such exposures of outdoor children increase to 
approximately 0 to 1 percent at the 0.08 ppm standard level, while the 
estimated range at the 0.09 ppm standard level increases to 
approximately 3 to 7 percent of outdoor children for these areas.
    (12) While recognizing that sensitive individuals may experience 
adverse but transient effects with a standard set at 0.08 ppm, no CASAC 
panel member supported selection of 0.07 ppm as the level of a primary 
standard. Of the

[[Page 38865]]

members who expressed their personal views, three indicated a 
preference for a level of 0.08 ppm, one for a range of 0.08 to 0.09 
ppm, three for a level of 0.09 ppm (with one of the three expressing a 
preference for selecting a form that would result in equivalent 
protection to the current standard), and one for a range of 0.09 to 
0.10 ppm, associated with public advisories for O3 levels at 
and above 0.07 ppm. Other CASAC panel members also expressed support 
for such public notices or advisories reflecting potential effects for 
extremely sensitive individuals associated with O3 levels as 
low as 0.07 ppm.
    These observations and conclusions resulted in the Administrator 
focusing in particular on the alternative levels of 0.08 ppm and 0.09 
ppm, having placed great weight on the fact that none of the CASAC 
panel members expressed support for a standard set below 0.08 ppm. In 
deciding between these two levels, the Administrator took into account 
quantitative estimates of the risks associated with attaining standards 
set at these levels for those effects for which such quantitative risk 
estimates could be developed. Other factors that were important in the 
Administrator's proposed decision include:
    (1) Quantitative estimates of 8-hour exposures of concern (i.e., at 
and above 0.08 ppm) associated with these standard levels.
    (2) The consistency of the clinical, field, and epidemiological 
studies, in which effects were seen not only from controlled exposures 
to 0.08 ppm, but also in ambient environments in which 8-hour average 
O3 concentrations ranged from above to below the 0.08 ppm 
level.
    (3) The importance of increased protection for those sensitive 
individuals who may experience respiratory symptomatic and functional 
effects at lower O3 concentrations than the population as a 
whole.
    (4) The uncertainties in considering the potentially more serious 
but as yet uncertain chronic effects.
    As discussed above in Unit II.A.3., EPA completed and made 
available for public comment supplemental exposure and risk assessments 
subsequent to the proposal. For any of the alternative standards 
considered in the assessment, the new estimates of exposures at and 
above 0.08 ppm are somewhat higher than those available at the time of 
proposal, while the new estimates of risks, for adverse effects 
including moderate and large decreases in lung function, moderate to 
severe respiratory symptoms, and hospital admissions for asthmatics, 
are lower. However, the relative differences in estimated exposures and 
risks between alternative standard levels remain about the same as at 
the time of proposal. Thus, while the Administrator's final decision 
takes into account the more recent assessments, the differences in the 
quantitative results between the initial and supplemental assessments 
do not fundamentally alter the basis for the judgments expressed at the 
time of proposal.
    To aid in comparing the public health protection associated with 8-
hour standards at the 0.08 ppm and 0.09 ppm levels, observations from 
the updated exposure and risk assessments for all nine urban areas 
evaluated are summarized below (assuming the third-highest 
concentration form, which was the upper end of the range of 
consideration for forms for the 0.09 ppm level).
    (1) The percentages of outdoor children exposed to O3 
concentrations at and above 0.08 ppm (at which increased nonspecific 
bronchial responsiveness, decreased pulmonary defense mechanisms, and 
indicators of pulmonary inflammation have been observed in humans) 
while engaged in moderate exertion are estimated to be approximately 3 
percent at the 0.08 ppm standard level, ranging from approximately 2 
percent to 10 percent in the nine areas, increasing to approximately 11 
percent at a standard level of 0.09 ppm, ranging from approximately 7 
percent to 29 percent in the nine areas.
    Updated risk estimates in terms of the percentages14 and 
numbers of outdoor children estimated to experience various health 
effects, and the total numbers of occurrences of these effects in 
outdoor children, upon attainment of these two alternative standards 
for all nine urban areas combined15 are as follows:
---------------------------------------------------------------------------

    14 These updated risk estimates in terms of the percentage of 
outdoor children in the nine urban areas are roughly comparable to 
the range of original estimates presented in Table 1 of the proposal 
for 1- and 5-expected-exceedance forms of the standards.
    15 Approximately 3.1 million outdoor children reside in these 
nine urban areas.
---------------------------------------------------------------------------

    (2) For moderate lung function (FEV1) decreases 
 15 percent, approximately 6 percent of outdoor children 
(180,000 children) would experience this effect one or more times per 
year (650,000 occurrences) at the 0.08 ppm standard level, increasing 
to approximately 8 percent of outdoor children (250,000 children and 
1,100,000 occurrences) at the 0.09 ppm standard level.
    (3) For large lung function (FEV1) decreases  
20 percent, approximately 2 percent of outdoor children (58,000 
children) would experience this effect one or more times per year 
(100,000 occurrences) at the 0.08 ppm standard level, increasing to 
approximately 3 percent of outdoor children (97,000 children and 
220,000 occurrences) at the 0.09 ppm standard level.
    (4) For moderate or severe pain on deep inspiration, approximately 
0.9 percent of outdoor children (27,000 children) would experience this 
effect one or more times per year (120,000 occurrences) at the 0.08 ppm 
standard level, increasing to over 1 percent of outdoor children 
(41,000 children and 220,000 occurrences) at the 0.09 ppm standard 
level.
    Many public commenters supported EPA's proposed level of 0.08 ppm 
for an 8-hour standard, including most public health associations and 
groups of medical professionals, many citizens, and some States and 
regional associations. There were also large numbers of commenters who 
expressed strong views in opposition to the proposed level. Of those 
who did not support the proposed 8-hour level, almost all commenters 
representing businesses and industry associations, many local 
governmental groups and private citizens, and some States either 
supported no change to the current standard or, if EPA were to replace 
the current 1-hour standard with an 8-hour standard, supported a level 
of 0.09 ppm directly or simply one that would be ``equivalent'' to the 
current standard. On the other hand, environmental groups, many 
citizens, and some medical professionals and researchers supported a 
level of 0.07 ppm for an 8-hour standard.
    In general, the issues raised by these groups of commenters can be 
addressed in three categories: Comments on the strength and adequacy of 
the health effects evidence upon which the proposed decision was based, 
comments on the quantitative exposure and risk assessments and the 
extent to which the assessments either over- or under-predict exposures 
and risks among sensitive populations, and judgments as to whether the 
differences in public health protection provided by alternative 
standards are significant from a public health perspective. Each of 
these categories of key issues is discussed separately below.
    With regard to the first category of comments, on the strength and 
adequacy of the health effects evidence, commenters who did not support 
the need for any increased protection beyond that provided by the 
current standard questioned the adequacy or highlighted the limitations 
of the

[[Page 38866]]

various types of health effects studies that have related O3 
exposures to adverse effects. For example, some commenters questioned 
the controlled human exposure studies, arguing that: Many such studies 
used patterns of exposures and exercise levels that are not 
representative of normal population exposures to ambient O3; 
some exposure chambers using artificially generated O3 may 
have been contaminated with other pollutants that could have accounted 
for some of the observed effects; and responses to elevated 
O3 levels were compared to responses to air with essentially 
no O3 rather than to background levels typical of ambient 
air. Some commenters argued that these flaws in the study designs would 
result in overestimating responses to non-background levels of ambient 
O3 or in erroneous findings of statistical significance. In 
contrast, others commented that because the chambers did not contain 
other pollutants and natural pulmonary irritants (e.g., pollens, dust) 
or a full range of environmental conditions (e.g., high temperatures 
and humidity) typical of ambient air, the results may underestimate the 
true impact of O3 in the ambient air.
    Some commenters also questioned the summer camp and other field 
studies and epidemiological studies reporting increased hospital 
admissions and emergency room visits, arguing that: The responses in 
these studies were inherently confounded by exposures to other 
pollutants, the camp studies did not differentiate activity levels of 
the participants, and linear regression down to or below background 
levels was unjustifiably used to analyze the results of the hospital 
admission studies. These commenters expressed the view that these and 
other flaws call into question any conclusions about whether the 
reported associations are causal. In contrast, other commenters argued 
that the hospital admissions reported in these studies are indicative 
of a pyramid of adverse health effects, including increased mortality, 
increased visits to emergency and outpatient departments and 
physicians, increased numbers of asthma attacks resulting in increased 
medication use, and increased numbers of restricted activity days and 
acute respiratory symptom days, that EPA has not adequately taken into 
account. The EPA notes that these comments are consistent with 
statistics published by the U.S. Department of Health and Human 
Services, which indicate that for every hospital admission of an 
individual with asthma for respiratory causes, there are more than five 
emergency and outpatient department visits and more than 20 office-
based physician visits (U.S. DHHS, 1996).
    With regard to studies related to pulmonary inflammation and 
chronic respiratory damage, some commenters argued that the linkage 
between repeated inflammatory responses and chronic respiratory damage 
was merely speculation, and, therefore, should not be considered as 
part of the basis for decisions on the primary standard. In contrast, 
others commented that animal studies had demonstrated that repeated 
pulmonary inflammation leads to degenerative or irreversible lung 
damage, that these studies are consistent with observations in human 
exposure studies, and, therefore, that they should be considered in 
decisions on the standard.
    The EPA notes that many of these comments did not reflect an 
integrative assessment of the evidence--the approach CASAC has 
historically urged EPA to follow--but rather a piecemeal look at each 
individual study or type of study, which tends to miss the strength of 
the entire body of evidence taken together. Other commenters did 
consider the body of evidence in a more integrative manner, and many of 
these commenters expressed the view that the body of evidence as a 
whole provided clear evidence of O3-related effects at and 
below O3 concentrations allowed by the current standard. 
Some commenters highlighted the large number of studies that 
demonstrate evidence of effects for prolonged exposures at and below 
0.08 ppm, and criticized EPA for giving too little weight to those 
studies which reported serious effects, but for which the data were not 
sufficient to do quantitative risk assessments.
    With regard to the second category of comments, on the exposure and 
risk assessments, a number of commenters raised concerns about key 
aspects of the assessments, including the exposure model, the 
development of concentration-response functions, the application of the 
risk model, and the measures of risk used to characterize the results 
of the assessments. With regard to the exposure model, a number of 
commenters claimed that: The model overestimates the exertion level 
that can be achieved by most children and outdoor workers and the 
fraction of time that these groups spend in moderate or heavy exertion; 
the model overestimates outdoor ambient exposures because fixed-site 
monitors overestimate outdoor personal exposures; and the air quality 
adjustment procedures used to simulate attainment of the standards are 
inappropriate or highly uncertain. Other commenters expressed concern 
that the exposure model may be significantly underestimating exposures 
for children and outdoor workers who repeatedly exercise due to 
limitations in the available human activity pattern data.
    As discussed in the proposal, EPA recognizes that the exposure 
model necessarily contains many sources of uncertainty, although every 
effort has been made to account for such uncertainties to the extent 
possible. In particular, the model incorporates and is sensitive to 
analytical procedures used to simulate spatial and temporal 
distributions of O3 concentrations that would occur as a 
result of an area just attaining any of the alternative standards 
addressed in the exposure assessment. These air quality adjustment 
procedures are based on generalized models intended to reflect the 
patterns of changes in distributions of O3 concentrations 
that have historically been observed in areas implementing control 
programs designed to attain the O3 NAAQS. The EPA recognizes 
that future changes in air quality distributions are area-specific, and 
will be affected by whatever specific control strategies are 
implemented in the future to attain the revised NAAQS. Thus, 
generalized models are expected to be more uncertain for any given area 
than when exposure results are aggregated across many areas (as was 
done across the nine urban areas analyzed in EPA's exposure 
assessment).
    Some commenters questioned the specific air quality adjustment 
procedure used in the initial and supplemental assessment16, 
and a few of these commenters recommended revisions or alternative 
procedures that they believed would be more representative of 
historical or projected future air quality patterns. As discussed in 
more detail in the Response to Comments, EPA acknowledges that both 
procedures used in the assessments result in projections of air quality 
that deviate to some degree from historical patterns of air quality 
changes observed in specific urban areas, and that other procedures may 
be more representative of air quality patterns in specific areas. While 
EPA will take these comments into account as future refinements are 
made to the air quality adjustment

[[Page 38867]]

procedures used in the exposure model, EPA believes, and CASAC 
concurred, that the procedures used in the assessments conducted as 
part of this review are reasonable given the uncertainties inherent in 
projecting future changes in air quality patterns.
---------------------------------------------------------------------------

    16 The initial risk assessment used both ``Weibull'' and 
``proportional'' air quality adjustment procedures, whereas the 
supplemental risk assessment used a ``proportional'' air quality 
adjustment procedure for all nine urban areas. In responding to 
comments on the air quality adjustment procedures, EPA also 
evaluated an alternative ``quadratic'' procedure (as discussed in 
the Response to Comments), which generally resulted in risk 
estimates between those from the Weibull and proportional 
procedures.
---------------------------------------------------------------------------

    In commenting on the air quality adjustment procedure used in the 
supplemental assessment, some commenters particularly focused on the 
results for two of the nine areas analyzed in which, contrary to 
results from the initial assessment, lower risks were estimated for the 
current standard as compared to the proposed standard. As discussed 
more fully in the Response to Comments, EPA believes that these results 
for each area cannot be distinguished within the sensitivity of the 
alternative air quality adjustment procedures used in the initial and 
supplemental assessments. Further, EPA notes that these two areas have 
much higher ratios of peak 1-hour to 8-hour O3 
concentrations than the vast majority of areas in which O3 
is monitored17, and it is thus reasonable to expect that 
generalized air quality adjustment procedures would be particularly 
uncertain for such areas.
---------------------------------------------------------------------------

    17 The two areas are Houston and parts of Los Angeles county, 
which are two of only six areas nationwide with peak 1- to 8-hour 
design value ratios greater than 1.5.
---------------------------------------------------------------------------

     Comments focusing on the development of concentration- response 
functions for use in the risk model have included a number of claims. 
Some commenters claimed that EPA inappropriately selected studies for 
developing the functions by excluding studies that reported lower 
response rates and by using only studies conducted by EPA scientists. 
Some commenters asserted that contaminants in the controlled exposure 
chambers may be responsible for some of the effects incorporated into 
the concentration-response functions for O3. Further, some 
commenters asserted that it was inappropriate to extrapolate the 
concentration-response functions to background levels or to develop 
concentration-response functions for symptomatic responses in children 
based on studies of such responses in adults.
    Of the comments focusing on the application of the risk model, some 
commenters claimed that the aggregate risk results were overstated 
because of: Many of the methodological problems noted in the above 
summary of comments, the failure to take into account the known 
attenuation of effects, and the assumption of an inappropriately low 
background concentration in calculating risks attributable to non-
background sources of O3. On the other hand, other 
commenters claimed that aggregate risk results were understated because 
of: Methodological problems, noted above, that underestimate exposures, 
limiting the analyses to only a subset of adverse health effects rather 
than estimating the full range of effects that have been attributed to 
O3, and by focusing only on nine urban areas rather than 
projecting risk reductions from alternative standards nationally.
    While EPA has included comprehensive responses to these comments in 
the Response to Comments, most of the issues and concerns raised by 
commenters concerning the health effects evidence and the methods used 
in the exposure and risk assessments are essentially restatements of 
concerns raised during the review of the Criteria Document and the 
development and review of these quantitative assessments as part of the 
preparation and review of the Staff Paper. EPA presented and the CASAC 
reviewed in detail the approaches used to assess exposure and health 
risk, the studies and health effect categories selected for which 
concentration-response functions were estimated, and the presentation 
of the exposure and risk results summarized in the Staff Paper. As 
stated in the proposal, EPA believes and CASAC concurred, that the 
general models selected to estimate exposure and risk are appropriate 
and that the methods used to conduct the exposure and risk assessments 
represent the state of the art. EPA does not believe that the exposure 
or risk assessments are fundamentally biased in one direction or the 
other as claimed in some of the comments.
    The Administrator and CASAC have recognized, however, that there 
are many uncertainties inherent in such assessments and that the 
resulting ranges of quantitative risk estimates do not reflect all of 
the uncertainties associated with the numerous assumptions inherent in 
such analyses (Wolff, 1995b). EPA summarized some of the most important 
caveats and limitations concerning both the exposure analyses and the 
risk assessments for lung function changes, respiratory symptoms, and 
hospital admissions in the proposal. A more complete discussion of 
assumptions and uncertainties is contained in the Staff Paper and 
technical support documents (Johnson et al., 1996 a,b; Whitfield et 
al., 1996; Richmond, 1997).
    With regard to the third category of comments, reflecting 
commenters' judgments as to whether the differences in public health 
protection of alternative standards are significant from a public 
health perspective, EPA notes that highly divergent judgments were 
expressed by different groups of commenters. A large number of 
commenters who expressed the view that the differences in public health 
protection were not significant or important enough to warrant any 
standard more stringent than the current standard used CASAC as the 
basis for their position, as discussed above in Unit II.B.1. on 
averaging time. Others cited small percentages of outdoor children and 
other sensitive groups likely to be affected based on EPA's assessment, 
or even smaller percentages as modified by analyses conducted by the 
commenter to correct perceived errors in the analyses. In contrast, 
other commenters cited large total numbers of children likely to be 
affected, not only for the subset of O3-related effects and 
the nine areas analyzed in EPA's assessments, but also for a broader 
array of related effects projected nationally.
    The core issue in this review of the primary O3 
standard, as stated by the Administrator at the time of proposal, is 
who is to be protected, and from what. Clearly, for pollutants, such as 
O3, that have no discernible thresholds for health effects, 
no standard can be risk-free. The Administrator's task is to select a 
standard level that will reduce risks sufficiently to protect public 
health with an adequate margin of safety since a zero-risk standard is 
neither possible nor required by the Act. As CASAC and the 
Administrator recognize, the selection of a specific standard level for 
such pollutants requires public health policy judgments in addition to 
determinations of a strictly scientific nature.
    In making such judgments, the Administrator rejects the notion that 
because standards cannot be risk-free they should not be revised to 
provide increased protection for sensitive populations, particularly 
including children in this case, when available evidence points to 
greater impacts on public health than had previously been demonstrated. 
In carefully reassessing both those risks to public health that can be 
quantified as well as those for which quantitative risk information is 
more limited, the Administrator has focused on the following 
comparisons between the degree of public health protection likely to be 
afforded by an 8-hour standard at the proposed level of 0.08 ppm and an 
alternative standard set at a level of 0.09 ppm (assuming the same 
third-highest concentration form):
    (1) Based on EPA's updated analyses of estimated moderate or large 
decreases

[[Page 38868]]

in lung function and moderate to severe pain on deep inspiration in 
outdoor children in nine urban areas (Richmond, 1997), a standard set 
at 0.09 ppm would allow approximately 40 percent to 65 percent more 
outdoor children to experience such effects than would a 0.08 ppm 
standard, and approximately 70 percent to 120 percent more occurrences 
of such effects in outdoor children per year.
    (2) While only relatively small percentages of outdoor children are 
estimated to experience such effects, the differences in these 
percentages between the two standard levels represent tens of thousands 
more children, and hundreds of thousands more occurrences of adverse 
effects in these children, in these nine urban areas alone, for a 0.09 
ppm standard as compared to a 0.08 ppm standard.
    (3) Based on EPA's updated risk assessment of increased hospital 
admissions in New York City (Richmond, 1997), a standard set at 0.09 
ppm would allow approximately 40 more excess hospital admissions of 
asthmatics within an O3 season in New York City for 
respiratory causes as compared to a 0.08 ppm standard, which represents 
approximately a 40 percent increase in excess O3-related 
admissions, but only approximately a 0.3 percent increase in total 
admissions of asthmatics. The EPA believes that while these numbers of 
hospital admissions are relatively small from a public health 
perspective, they are indicative of a pyramid of much larger numbers of 
related O3-induced effects, including respiratory-related 
hospital admissions among the general population, emergency and 
outpatient department visits, doctors visits, and asthma attacks and 
related increased use of medication that are important public health 
considerations.
    (4) Based on EPA's exposure analyses in the nine urban areas, a 
standard set at 0.09 ppm would allow more than three times as many 
children to experience 8-hour average exposures of concern as would a 
0.08 ppm standard, with the number of outdoor children likely to 
experience such exposures increasing from approximately 100,000 to more 
than 300,000 in the nine urban areas alone, representing an increase 
from approximately 3 percent to approximately 11 percent of the outdoor 
children likely to experience such exposures.
    (5) These exposures of concern are judged by EPA to be an important 
indicator of the public health impacts of those O3-related 
effects for which information is too limited to develop quantitative 
estimates of risk, but which have been observed in humans at a level of 
0.08 ppm for 6- to 8-hour exposures. Such effects include the 
following: increased nonspecific bronchial responsiveness (related, for 
example, to aggravation of asthma), decreased pulmonary defense 
mechanisms (suggestive of increased susceptibility to respiratory 
infection), and indicators of pulmonary inflammation (related to 
potential aggravation of chronic bronchitis or long-term damage to the 
lungs).
    (6) To put these risks and exposures into broader perspective, EPA 
notes that approximately 46 million more people, including 
approximately 13 million more children and 3 million more individuals 
with asthma, live in areas that would not attain a 0.08 ppm standard 
compared to a 0.09 ppm standard. The general population as well as 
children and asthmatics would breathe cleaner air as a direct result of 
control measures designed to bring areas into attainment with the 
proposed standard.18
---------------------------------------------------------------------------

    18 The EPA anticipates that additional people would be protected 
through regional measures adopted for purposes of an 8-hour, 0.08 
ppm standard.
---------------------------------------------------------------------------

    While recognizing the inherent uncertainties in these estimates, 
and after taking into account the range of views and judgments 
expressed in the public comments, the Administrator finds the public 
health impacts described in the proposal, as updated above, to be 
important and sufficiently large as to warrant a standard set at a 
level of 0.08 ppm, as proposed.
    The Administrator recognizes the views of those who argue that 
similarly large improvements in public health protection would result 
from a standard set at 0.07 ppm as compared to the proposed standard, 
such that, based on the same reasoning, the evidence warrants a 
standard set at 0.07 ppm. In considering these views, the Administrator 
gives significant weight to the following considerations:
    (1) No member of the CASAC panel of experts supported a standard 
set lower than 0.08 ppm, specifically after considering a range of 
alternative standards that included 0.07 ppm.
    (2) The most certain O3-related effects, while judged to 
be adverse, are transient and reversible (particularly at O3 
exposures below 0.08 ppm), and the more serious effects with greater 
immediate and potential long-term impacts on health are less certain, 
both as to the percentage of individuals exposed to various 
concentrations who are likely to experience such effects and as to the 
long-term medical significance of these effects.
    (3) As many commenters have noted, based on information in the 
Criteria Document with regard to ambient concentrations of 
O3 from background sources, an 8-hour standard set at a 0.07 
ppm level would be closer to peak background levels that infrequently 
occur in some areas due to nonanthropogenic sources of O3 
precursors, and thus more likely to be inappropriately targeted in some 
areas on such sources.
    After taking into account the public comments, and for the reasons 
outlined above, the Administrator finds that a standard set at a level 
of 0.07 ppm is not requisite to protect public health with an adequate 
margin of safety.
    3. Form. The form of the current 1-hour, 0.12 ppm standard is a 
``1-expected-exceedance'' form. That is, the current standard is based 
on the expected19 number of days per year, on average over 3 
years, on which the level of the standard is exceeded, and limits that 
number of expected exceedances to be less than or equal to 1.0.
---------------------------------------------------------------------------

    19 The term ``expected'' means that the numbers of exceedances 
per year are averaged over 3 years and may be calculated using 
specific adjustments to account for missing data.
---------------------------------------------------------------------------

    In evaluating alternative forms for the primary standard, the 
adequacy of the public health protection provided was the 
Administrator's foremost consideration. The Administrator also 
recognized, however, that concerns have been raised with the current 
form since it was promulgated in 1979 due to the inherent lack of year-
to-year stability in the measure of air quality on which the 1-
expected-exceedance form is based.20 The CASAC specifically 
took such concerns into account in recommending that the current form 
be revised and in noting that a more robust, concentration-based form 
would minimize such instability and provide some insulation from the 
impacts of extreme meteorological events that are conducive to 
O3 formation (Wolff, 1995b). Such instability can have the 
effect of reducing public health protection by disrupting ongoing 
implementation plans and associated control programs.
---------------------------------------------------------------------------

    20 The 1-expected-exceedance form essentially requires the 
fourth-highest air quality value in 3 years, based on adjustments 
for missing data, to be less than or equal to the level of the 
standard for the standard to be met at an air quality monitoring 
site.
---------------------------------------------------------------------------

    As discussed in the proposal, based on information presented in 
sections IV. and V.I of the Staff Paper and the advice of CASAC, the 
Administrator focused her consideration on the following alternatives:
    (1) Revising the current 1-expected-exceedance form of the standard 
to

[[Page 38869]]

allow for multiple (up to five) expected exceedances per year, averaged 
over 3 years. A multiple-exceedance form would be based on a less 
extreme air quality statistic and, thus, would increase the stability 
of the expected-exceedance form.
    (2) Adopting a concentration-based statistic, such as the 3-year 
average of the nth-highest daily maximum 8-hour average O3 
concentration, as an alternative to an expected exceedance statistic. 
Air quality analyses presented in the Staff Paper indicate that the 3-
year averages of the annual third-, fourth-, and fifth-highest daily 
maximum 8-hour concentrations would provide approximately the same 
health protection as the 3-, 4-, and 5-expected-exceedance forms 
averaged over the same period, respectively.
    It was the consensus of the CASAC Panel that this range of 
allowable exceedances (i.e., up to 5 exceedances), and the 
consideration of comparable concentration-based forms, was appropriate. 
Further, CASAC acknowledged that selecting from within this range of 
alternative forms is a policy judgment, especially given the nature of 
the health effects and the absence of a ``bright line'' that clearly 
differentiates between acceptable and unacceptable risks within this 
range. All 10 CASAC Panel members who expressed specific opinions on 
the form of the standard favored one that would allow for multiple 
exceedances (Wolff, 1995b).
    In reaching her proposed decision on the form of an 8-hour standard 
set at 0.08 ppm, the Administrator had to choose a specific form within 
the range of up to 5 allowable exceedances or up to the comparable 
fifth-highest concentration, and either an exceedance-based or a 
concentration-based form. As discussed in the proposal, in considering 
possible forms within the range of 1 to 5 exceedances (or their 
concentration-based counterparts) the Administrator took into 
consideration aggregate risk estimates for those health effects for 
which quantitative risk analyses have been done; estimated exposures 
associated with those effects for which no quantitative risk estimates 
could be developed; and the magnitude of peak measurements of 8-hour 
average O3 concentrations, and the number of days on which 
the level of the standard would likely be exceeded, based on an 
analysis of historical air quality data (Freas, 1996). In considering 
exposure and risk estimates available at the time of proposal for 1- 
and 5-expected-exceedance forms, the Administrator noted that the level 
of the standard is a more dominant factor in determining the degree of 
exposure and risk reductions achieved, with the form being associated 
with smaller differences in risk estimates within a continuum of risk. 
In considering air quality comparisons for standards across the range 
of forms considered, the Administrator focused in particular on the 
extent to which alternative forms would limit the number of days in 
which the level of the standard would be exceeded in areas that just 
attain the standard21, and the magnitude of peak 8-hour 
average O3 concentrations22 that would occur in 
such areas.23 More specifically, the Administrator took into 
consideration the percentage of monitoring sites just attaining an 8-
hour, 0.08 ppm standard that would have 8-hour peak O3 
concentrations above a benchmark level of 0.09 ppm. This benchmark 
level is the upper end of the range of levels endorsed by CASAC for an 
8-hour O3 standard. The Administrator believes, given the 
uncertainties associated with this kind of complex health decision, 
that it is an appropriate goal to limit the percentages of areas 
experiencing such daily peaks.
---------------------------------------------------------------------------

    21 Areas that ``just attain the standard'' are defined as those 
whose design value falls between 0.075 and 0.084 ppm.
    22 Peak 8-hour average concentrations are defined in terms of 
the fourth-highest daily maximum concentration in 3 years (i.e., the 
design value for the current 1-expected-exceedance form of the 
standard).
    23 The results of these air quality analyses are presented in 
Freas (1996) and summarized in the proposal for the third- and 
fifth-highest concentration forms and the 3- and 5-expected-
exceedance forms. Based on these considerations, and the air quality 
comparisons in particular, the Administrator judged that the middle 
of the range of exceedances considered, three expected exceedances, 
or the comparable third-highest concentration, represented a 
reasonable policy choice, and proposed the 3-year average of the 
annual third-highest daily maximum 8-hour average O3 
concentrations as the form of the standard. In recognition of a 
range of views on the degree of health protection that would be 
appropriate, she also solicited comment on other concentration-based 
forms, including the second-, fourth-, and fifth-highest 
concentration forms.
---------------------------------------------------------------------------

    In choosing to propose a concentration-based form, the 
Administrator recognized the advantages of a concentration-based form 
over an exceedance-based form. As discussed in the proposal, the 
principal advantage of a concentration-based form is that it is more 
directly related to the ambient O3 concentrations that are 
associated with health effects. That is, given that there is a 
continuum of effects associated with exposures to varying levels of 
O3, the extent to which public health is affected by 
exposure to ambient O3 is related to the actual magnitude of 
the O3 concentration, not just whether the concentration is 
above a specified level. With an exceedance-based form, days on which 
the ambient O3 concentration is well above the level of the 
standard are given equal weight to those days on which the 
O3 concentration is just above the standard (i.e., each day 
is counted as 1 exceedance), even though the public health impact on 
the two days is significantly different. With a concentration-based 
form, days on which higher O3 concentrations occur would 
weigh proportionally more than days with lower O3 
concentrations, since the actual concentrations are used directly in 
determining whether the standard is attained. A concentration-based 
form also has greater temporal stability than the expected-exceedance 
form and, thus, would facilitate the development of more stable 
implementation programs by the States.
    As discussed above in Units II.A.3. and II.B.2., EPA completed and 
made available for public comment supplemental exposure and risk 
assessments subsequent to the proposal. These updated assessments, 
which specifically analyzed the third- and fifth-highest concentration-
based forms, aid in comparing the differences in public health 
protection among alternative concentration-based forms within the range 
considered in the proposal for 8-hour, 0.08 ppm standards. Based on 
these updated assessments, the Administrator again notes that the level 
of the standard is the more dominant factor in determining the degree 
of risk reduction achieved, with these alternative forms being 
associated with much smaller differences in risk estimates within a 
continuum of risk. For example, within the nine urban areas included in 
the risk assessment, approximately 180,000 outdoor children would 
experience moderate lung function (FEV1) decreases 
 15 percent upon attainment of an 8-hour, 0.08 ppm standard 
with a third-highest concentration form, compared to approximately 
200,000 outdoor children with a fourth-highest concentration form and 
220,000 outdoor children with a fifth-highest concentration form.
    The public comments include a large number that specifically 
addressed the form of the standard. Those commenters who expressed 
views on the form of the standard can be divided into three groups, 
according to the level of 8-hour standard and the relative degree of 
public health protection that the commenter supported. These groups 
include: Commenters who supported an 8-hour, 0.08 ppm standard to 
provide increased public health protection relative to the current 
standard;

[[Page 38870]]

commenters who supported either an 8-hour, 0.09 ppm standard, or simply 
an 8-hour standard ``equivalent'' to the current standard; and 
commenters who supported an 8-hour, 0.07 ppm standard to provide a 
greater margin of safety than that afforded by the proposed standard.
    The first group included many private citizens, some medical 
professionals and researchers, and some States and local governmental 
groups. While a number of commenters in the first group specifically 
supported the proposed third-highest concentration form, generally for 
the reasons presented in the proposal, others supported either a 1-
expected-exceedance form or a concentration-based form in the upper 
part of the range (i.e., the fourth- or fifth-highest forms). The 
second group of commenters, which included many local governmental 
groups and private citizens, some States, and most commenters 
representing businesses and industry associations, almost exclusively 
supported a concentration-based form in general, and a form in the 
upper part of the range (or above the range) in particular. In sharp 
contrast, the third group of commenters, which included environmental 
groups, many private citizens, and some medical professionals and 
researchers, almost exclusively supported a 1-expected-exceedance form 
in conjunction with an 8-hour, 0.07 ppm standard to provide the largest 
margin of safety within the range of alternative standards considered.
    To the extent that the second and third groups of commenters argued 
for a different level than the Agency adopts today, the Administrator 
disagrees with their comments for the reasons set forth in the 
discussion of the standard level above in Unit II.B.2. To the extent 
that they argued for more than 5 exceedances (or the concentration-
based equivalent), the Administrator disagrees with their views because 
such forms fall outside the range recommended by CASAC and would 
provide less public health protection than she deems appropriate. To 
the extent that the second and third groups of commenters addressed the 
merits of particular forms within the range of forms considered in the 
proposal, they raised points similar to those raised by commenters in 
the first group. These points are discussed below.
    Among the commenters in the first group (i.e., those supporting an 
8-hour, 0.08 ppm standard to provide increased public health 
protection), many felt that there was no compelling basis for selecting 
the third-highest rather than the fourth- or fifth-highest 
concentration-based form. These commenters frequently quoted CASAC's 
closure letter (Wolff, 1995b) as stating ``that there is no bright 
line' which distinguishes any of the proposed standards (either the 
level or the number of exceedances) as being significantly more 
protective of public health,'' and that ``the selection of a specific 
level and number of allowable exceedances is a policy judgment.'' In 
general, these commenters did not give weight to the air quality 
comparisons that were a major consideration in the Administrator's 
decision to propose the third-highest concentration form. Some 
commenters seem to view such air quality comparisons, particularly with 
regard to pollutants such as O3 that have no discernible 
threshold of effects, as relating more to people's perceptions of how 
well air pollution is controlled than to any objective measure of 
actual risks to public health.
    These commenters made a number of points in questioning the need to 
specify an 8-hour, 0.08 ppm standard in terms of the third-highest 
rather than the fourth- or fifth-highest concentration form. Many noted 
that a change to an 8-hour averaging time in and of itself would 
appropriately focus air quality management programs on prolonged 
exposures of most concern. Further, many noted that a level of 0.08 
ppm, regardless of the form within the range of forms considered in the 
proposal, would provide significantly increased protection from 
O3-related risks to public health associated with acute 
effects (i.e., those resulting from short-term and prolonged exposures) 
for which they believe there is sufficient evidence to be used as a 
basis for a standard at this time. Some of these commenters expressed 
the view that the potential for chronic effects (i.e., those resulting 
from long-term exposures) would be better addressed through continued 
research, rather than by adding a greater margin of safety to a revised 
standard based primarily on effects of short-term and prolonged 
exposures. Many of these commenters recognized, as did EPA in the 
proposal, that there is a continuum of risks associated with 
O3 exposures, that no standard can therefore be risk-free, 
and that there are large uncertainties in any estimates of the degree 
of protection associated with alternative forms. In general, these 
commenters also noted that, for the same reasons, CASAC advised that 
the selection of a form from within the range considered in the 
proposal was a policy judgment, not one that could be decided on the 
basis of science alone. In essence, these commenters argued that a more 
restrictive form than the upper part of the range endorsed by CASAC is 
not requisite to protect public health.
    In contrast, other commenters in the first group (i.e., those 
supporting an 8-hour, 0.08 ppm standard) supported either the proposed 
third-highest or second-highest concentration form or a 1-expected-
exceedance form. These commenters generally gave greater weight to 
limiting the magnitude of peak O3 concentrations and the 
number of days on which the standard level would be exceeded in areas 
meeting such a standard, and, in some cases, to providing a greater 
margin of safety to account for potential chronic effects. Such views 
suggest that limiting the number of days on which the standard level 
would be exceeded, for example, is an important factor in risk 
communication and in the public's understanding of the degree to which 
a standard protects people from exposures to O3 that may 
interfere with their ability to engage in normal activities or may 
result in the need for increased medication or medical treatment, 
especially for those individuals with asthma or other respiratory 
diseases. As discussed above in this unit, although some of these 
commenters felt that the third-highest concentration form would protect 
public health while also providing increased stability, others 
expressed concern that public health could be compromised by any form 
that allowed for multiple exceedances of the standard. The advantages 
of forms that allow for multiple exceedances, thus providing increased 
stability as discussed in the proposal, and the views of the CASAC 
panel members who expressed opinions, all of whom favored such forms, 
were not given weight by commenters within this group who supported a 
1-expected-exceedance form.
    The Administrator has carefully reassessed the relative risks to 
public health of specific forms within the range of the second- to 
fifth-highest concentration forms or their exceedance-based 
equivalents, taking into account the public comments summarized above, 
and the advice from CASAC Panel members that the current form be 
replaced by a form that allows multiple exceedances. In doing so, the 
Administrator focused on the following considerations:
    (1) The CASAC advised that concentration-based forms, within the 
range considered up to the fifth-highest concentration form, are 
appropriate for a health-based primary O3 standard, and that 
selection from within this range is a policy judgment that cannot be 
based

[[Page 38871]]

on science alone. This advice reflects CASAC's recognition that 
O3 exhibits a continuum of effects, such that there is no 
discernible threshold above which public health protection requires 
that no exposures be allowed or below which all risks to public health 
can be avoided. The CASAC also recognized that a concentration-based 
form would increase the stability of the standard by providing some 
insulation from the impacts of extreme meteorological events (Wolff, 
1995b).
    (2) Estimates of the differences in risk to public health, for 
those effects that could be considered quantitatively, within a range 
of alternative forms from the second- to fifth-highest concentrations 
(for an 8-hour, 0.08 ppm standard) are relatively small compared to the 
differences between alternative levels. In other words, the choice of 
level is substantially more important to the degree of public health 
protection afforded by the standard than the choice of form from within 
this range of forms.
    (3) Measures that distinguish between the alternatives within the 
range of the second- to fifth-highest forms, based on air quality 
analyses, reflect considerations related to how some individuals 
understand the degree to which an air quality standard protects public 
health. These considerations are a distinct aspect of risk 
communication to individual citizens even though the days on which 
exceedances occur are accounted for in EPA's quantitative assessments 
of risks to public health.
    (4) To assess the comparative effect of all forms within the range 
of the second- to fifth-highest concentration forms, EPA considered air 
quality comparisons for all such forms (Freas, 1996). These comparisons 
(based on 1993 to 1995 data) show that 8-hour, 0.08 ppm second- and 
third-highest concentration standards are very similar in that each 
standard limits the percent of monitoring sites that would experience 
peak days above the benchmark level of 0.09 ppm to 1 percent of such 
sites, and the number of days on which the standards would likely be 
exceeded in the worst of 3 years would be no more than 6 and 7, 
respectively. While less restrictive than either of these standards, an 
8-hour, 0.08 ppm fourth-highest concentration standard would be 
significantly more restrictive than a fifth-highest standard. For 
example, the 8-hour, 0.08 ppm fourth-highest concentration standard 
would limit the percent of monitoring sites that would experience peak 
days about the benchmark level of 0.09 ppm to 8 percent of such sites, 
and the number of days on which the standards would likely be exceeded 
in the worst of 3 years would be no more than nine. In comparison, the 
fifth-highest concentration standard would limit the percent of 
monitoring sites that would experience peak days about the benchmark 
level of 0.09 ppm to 17 percent of such sites, and the number of days 
on which the standards would likely be exceeded in the worst of 3 years 
would be no more than 11.
    (5) The extent to which the alternatives within the range of the 
second- to fifth-highest concentration forms provide protection against 
the more serious, but less certain effects that have been associated 
with exposure to O3, including potential chronic effects, 
cannot be quantitatively assessed at this time. Given that all such 
forms would result in significant reductions in exposures to 
O3 at and above 0.08 ppm (the level where suggestive 
evidence of such effects is available), any form within this range 
would provide some margin of safety against these effects.
    Based on these considerations, the available health effects 
evidence, the quantitative assessments contained in the Criteria 
Document, Staff Paper, and supplemental analyses and supporting 
documents, and the range of views and judgments expressed in the public 
comments on the appropriate form, the Administrator has reconsidered 
the form of the standard that is requisite to protect public health 
with an adequate margin of safety. As an initial matter, the 
Administrator has decided to adopt a concentration-based form which 
allows for more than one exceedance. While the Adminstrator understands 
the views of the many citizens who are concerned about a standard that 
would allow for multiple days on which the level of the standard may be 
exceeded, the Administrator concludes that such concerns are more 
relevant for pollutants that exhibit a clear threshold of effects than 
for pollutants such as O3 that exhibit a continuum of 
effects. The Administrator believes that the public health risks 
associated with such pollutants can be appropriately addressed through 
a standard that allows for multiple exceedances to provide increased 
stability, but that also significantly limits both the number of days 
on which the level may be exceeded and the magnitude of such 
exceedances. This approach recognizes that exposures associated with 
such exceedances are already reflected in the exposure and risk 
assessments that were an important consideration in selecting a 0.08 
ppm level for the primary O3 standard, and that increased 
stability in the standard is important to avoid disruption to ongoing 
control programs, and thus to maintain ongoing public health 
protection.
    Having again concluded that a concentration-based O3 
standard that allows for multiple exceedances is appropriate, the 
Administrator considered the extent to which the form of an 8-hour 
standard should be selected so as to provide a margin of safety against 
possible, but uncertain chronic effects. The Administrator carefully 
considered the views of the many commenters who emphasized the 
uncertainties in the evidence, primarily from laboratory animal 
studies, that was available in this review of the criteria and 
standards to relate long-term exposures to ambient levels of 
O3 to possible chronic effects in humans. These commenters, 
as did CASAC, advised that further research into potential chronic 
effects in humans should be continued, and the results considered in 
the next review of the O3 standard. The Administrator is 
persuaded that the difference between the margins of safety for these 
potential chronic effects afforded by the alternatives within the range 
of the second- to fifth-highest concentration forms is not well enough 
understood at this time to use as the basis for choosing the most 
restrictive forms (i.e., the second- or third-highest concentration 
form). On the other hand, the Administrator also judges that the 
relatively large percentage of sites that would experience 
O3 peaks above a benchmark level of 0.09 ppm even when 
attaining a fifth-highest concentration standard and the number of days 
on which the level of a fifth-highest concentration standard may be 
exceeded argue against choosing that form, which is the least 
restrictive within the range considered.
    For the reasons outlined above, and taking into account the range 
of views in the public comments, the Administrator concludes that an 
intermediate form, the fourth-highest concentration form, would serve 
to appropriately balance these public health considerations in 
conjunction with the 8-hour averaging time and 0.08 ppm level selected, 
as discussed above in Units II.B.1. and II.B.2., that are of primary 
importance in determining the degree of public health protection 
afforded by the standard. In addition, the Administrator notes that 
based on an analysis of air quality in counties that would attain an 8-
hour, 0.08 ppm fourth-highest concentration standard (based on 1993-
1995 data), over 99 percent of such counties would be expected to have 
four or fewer days on which the level of the standard is exceeded in an 
average year (Freas,

[[Page 38872]]

1997). This number of exceedances is clearly within the range of 
multiple exceedances that CASAC judged to be appropriate for a health-
based primary O3 standard. Thus, in the Administrator's 
judgment, based on the information currently available, an 8-hour, 0.08 
ppm standard with a fourth-highest concentration form will protect 
public health with an adequate margin of safety.
    In the proposal, which maintained the current approach of using air 
quality data from the monitor measuring the highest O3 
concentrations in an area to determine whether the primary standard for 
O3 is attained, the Administrator solicited comment on the 
alternative of using some form of averaging across monitors. As 
discussed in the proposal, EPA recognized that during the review of the 
Staff Paper, a number of commenters suggested that averaging across 
monitors might be appropriate to increase the degree to which 
monitoring data used in determining attainment of the standard reflects 
population exposure and aggregate population health risk. Further, 
these commenters suggested that averaging data from multiple monitors 
in an area would produce a more stable measure of air quality and would 
take into account broader population exposure patterns across an area 
than would the current approach of considering data from each monitor 
independently.
    The Administrator did not propose the use of spatial averaging 
because of concerns outlined in the proposal including: The difficulty 
in determining an appropriate level for a spatially averaged primary 
standard given that the bulk of the human health effects evidence 
supporting a decision on an appropriate O3 standard is based 
on controlled human exposure studies that relate known O3 
exposures directly to responses in individuals; and questions as to 
whether adequate health protection would be provided to individuals 
within the populations that live or work in communities that routinely 
experience higher O3 concentrations within a broad 
metropolitan area.
    To address these two concerns, it would be necessary to define 
criteria for geographic locations or communities (e.g., spatial 
averaging zones) within which the use of spatially averaged 
O3 data would be acceptable. Such criteria would be 
important since O3 air quality concentrations can vary 
significantly across most urban areas. The lowest concentrations 
typically occur in the urban center and in locations near O3 
precursor sources, mid-range concentrations in neighborhoods and 
locations surrounding the urban center, and peak concentrations are 
typically measured downwind along the outermost suburban regions of the 
urban area. Also, the location of residences, schools, parks, and other 
places where individuals might be exposed more frequently to ambient 
O3 concentrations of concern would be an important 
consideration. Unless the O3 concentration gradients within 
each spatial averaging zone were relatively homogeneous, there may be 
significant numbers of sensitive individuals exposed to high 
O3 concentrations in areas where the spatial average 
indicates that the overall air quality is acceptable.
    In the proposal, EPA also noted the need to help State and local 
governments devise different O3 monitoring networks by 
revising relevant regulations and guidance, should spatial averaging be 
adopted. This would likely involve defining general criteria for 
monitoring network design, siting, and spatial averaging zones in 
nationally implementable terms, with case-by-case evaluation of each 
monitoring network. The EPA recognized that this activity would place 
additional burdens on State and local air quality management districts.
    In soliciting comment on whether it would be desirable to adopt 
some form of spatial air quality averaging for O3, the 
Administrator also solicited comment on specific alternative approaches 
that could be used to address the issues of concern. In particular, the 
Administrator was interested in analyses that inform questions about 
monitoring network design, siting requirements, and approaches for 
specification of spatial averaging zones; the distribution of public 
health protection that would result from such alternative approaches; 
and the extent to which the level of the standard would need to be 
adjusted, if any, to provide public health protection consistent with 
the level of protection contemplated in the proposal.
    The EPA received many comments on the subject of using spatially 
averaged data to determine when the primary standard for O3 
is attained. Commenters from business and industry associations 
frequently supported the use of spatially averaged data, as did many 
local governments and a small number of States, principally because it 
would provide a more stable air quality indicator and would better 
represent population exposure and risk. Some of these commenters felt 
that the use of spatial averaging would be consistent with the use of 
risk assessment as a policy tool for standard setting. Many of these 
commenters agreed that the heterogeneity of O3 
concentrations across geographic areas would need to be addressed by 
network design, with a few expressing the opinion that this would not 
be an insurmountable problem given that there is continual movement of 
monitors within existing networks. Some commenters suggested averaging 
approaches that included the use of population weighting of monitored 
data, and some supported the use of a public health information system 
to allow individuals residing in ``hot spot'' areas to reduce their 
exposures to O3 concentrations of concern.
    In contrast, environmental associations, public health 
professionals, most States, and many individuals voiced strong concerns 
that the use of spatially averaged data would routinely allow 
individuals who live or work in communities with consistently higher 
O3 levels than those occurring across the broader urban area 
to be exposed to concentrations of concern. Many of these commenters 
raised the issue of environmental equity, expressing the view that 
communities with consistently higher O3 concentrations 
typically are composed predominantly of individuals of lower 
socioeconomic status, or are composed of a predominantly minority 
population. The EPA notes that this view is not consistent with the air 
quality data discussed earlier in this unit, in that O3 
concentrations are typically lower in urban centers than in locations 
surrounding or downwind of urban centers. Some commenters also raised 
concerns about the complexity and burdens associated with redesigning 
existing monitoring networks.
    Taking into account the comments received, the Administrator does 
not find that the issues of concern, as outlined in the proposal and 
above, have been adequately addressed in this review of the 
O3 standard. In particular, while EPA strongly agrees with 
the importance of public health advisories in addition to adequately 
protective standards, relying on the use of public health advisories to 
provide information for at-risk populations who may consistently be 
exposed to localized O3 concentrations of concern is 
considered by the Administrator to be an insufficient approach to 
protecting public health with an adequate margin of safety. Further, 
the suggested use of population weighting of monitored data may, in 
many cases, be insufficiently sensitive to local O3 
variations to ensure adequate protection of these populations from 
localized O3 concentrations. Thus, the revised O3 
standard will maintain the current

[[Page 38873]]

approach of using air quality data from the monitor measuring the 
highest O3 concentrations in an area to determine whether 
the standard is attained within an area.
    The EPA has also considered spatial averaging in the context of the 
decision to revise the PM NAAQS, in part, by adopting a form of an 
annual standard for fine particles (i.e., PM2.5) that allows 
for spatial averaging within appropriate criteria. It is important to 
note that different considerations apply in these two cases. One 
principal difference is the nature of the health effects evidence for 
O3 and PM2.5. When considering averaging 
approaches for O3, it should be recognized that much of the 
human health effects evidence supporting the O3 standard is 
based on controlled human exposure studies that relate individual 
O3 exposures directly to responses in individuals, whereas 
the health effects evidence supporting the PM2.5 standards 
is from epidemiological studies relating community measures of 
PM2.5 concentrations to population-wide responses. Thus, 
information available for determining an appropriate level of a 
standard in these two cases is predominantly individual-oriented in the 
case of O3 and community-oriented in the case of 
PM2.5. As a consequence, additional research and exposure 
and risk assessments beyond those available in this review would be 
necessary to provide a basis for further consideration of a spatially 
averaged standard for O3. The EPA will continue to explore 
this approach.
    Another important difference between the O3 and PM 
standards is that the suite of annual and 24-hour PM2.5 
standards permits the use of the 24-hour PM2.5 standard, 
which would not be spatially averaged, as a backstop to control 
localized ``hot spots,'' whereas a single O3 standard does 
not allow for such a dual approach. Also, EPA notes that the existence 
of an established, extensive O3 monitoring network would 
require substantial redesigning and relocation of monitors for the 
purpose of spatial averaging, in contrast to the current absence of 
such a network for PM2.5 which can be newly designed to 
address community-oriented monitoring from the outset.
    As discussed in the proposal, the Administrator recognizes that no 
standard within the range of levels and forms considered in this 
review, including the selected standard, is risk free, due to the 
continuum of risk likely posed by exposures to ambient O3 
potentially down to background levels. Accordingly, consistent with 
CASAC advice, the Administrator solicited comment in the proposal on 
elements of an enhanced public health advisory system. The 
Administrator believes that the information that could be made 
available through such a public health advisory system would be 
particularly useful to extremely sensitive individuals in making 
personal decisions about avoiding exposures with the potential to cause 
transient adverse effects on days when 8-hour average O3 
concentrations are predicted to be at or near the level of the 
standard. Approaches to developing an enhanced system, and comments 
received on such approaches, are discussed in Unit II.C. of this 
preamble.
    4. Final decision on the primary standard. After carefully 
considering the information presented in the Criteria Document and the 
Staff Paper, the advice and recommendations of CASAC, public comments 
received on the proposal, and for the reasons discussed above, the 
Administrator is replacing the existing 1-hour, 0.12 ppm primary 
standard with a new 8-hour, 0.08 ppm primary standard. The new 8-hour 
standard will become effective September 16, 1997.
    The 8-hour, 0.08 ppm primary standard will be met at an ambient air 
quality monitoring site when the 3-year average of the annual fourth-
highest daily maximum 8-hour average O3 concentration is 
less than or equal to 0.08 ppm. Data handling conventions are specified 
in a new Appendix I to 40 CFR part 50 as discussed in Unit VI below.
    In the proposal, EPA proposed that the revocation of the existing 
1-hour O3 standard be delayed for certain purposes until EPA 
had approved State Implementation Plans to implement the new 8-hour 
O3 standard. EPA had proposed continuing the applicability 
of the 1-hour standard in this way in order to facilitate continuity in 
public health protection during the transition to a new standard. (See 
Memorandum from John S. Seitz to Mary D. Nichols, November 20, 1996; 
Docket No. A-95-58, item II-B-3.) Also, at the time of the proposal of 
the new O3 standard, EPA had proposed an interpretation of 
the Act in the proposed Interim Implementation Policy (61 FR 65764, 
December 13, 1996) under which the provisions of subpart 2 of part D of 
Title I of the Act would not apply to existing O3 
nonattainment areas once a new O3 standard becomes 
effective.
    In light of comments received regarding the interpretation proposed 
in the Interim Implementation Policy, EPA has reconsidered that 
interpretation and now believes that the Act should be interpreted such 
that the provisions of subpart 2 continue to apply to O3 
nonattainment areas for purposes of achieving attainment of the current 
1-hour standard. As a consequence, the provisions of subpart 2, which 
govern implementation of the 1-hour O3 standard in 
O3 nonattainment areas, will continue to apply as a matter 
of law for so long as an area is not attaining the 1-hour standard. 
Once an area attains that standard, however, the purpose of the 
provisions of subpart 2 will have been achieved and those provisions 
will no longer apply. However, the provisions of subpart 1 of part D of 
Title I of the Act would apply to the implementation of the new 8-hour 
O3 standards.
    To facilitate the implementation of those provisions and to ensure 
a smooth transition to the implementation of the new 8-hour standard, 
the 1-hour standard should remain applicable to areas that are not 
attaining the 1-hour standard. Therefore, the 1-hour standard will 
remain applicable to an area until EPA determines that it has attained 
the 1-hour standard, at which point the 1-hour standard will no longer 
apply to that area.

C. Communication of Public Health Information

    Information on the public health implications of ambient 
concentrations of criteria pollutants is currently made available 
primarily through two EPA programs. The first program is designed to 
prevent ambient pollutant concentrations from reaching the significant 
harm level (i.e., an exposure level that constitutes an imminent and 
substantial endangerment to public health). The second program is the 
Pollutant Standards Index (PSI),24 which is a health 
advisory system. The proposal focused on the potentially expanded use 
of the PSI in regard to allowing sensitive individuals to reduce their 
risk of exposure. Currently, EPA and local officials use the PSI as a 
public information tool to advise the public about the general health 
effects associated with different pollution levels and to describe 
whatever precautionary steps may need to be taken if air pollution 
levels rise into the unhealthful range. By notifying the public when a 
PSI value exceeds 100 (which corresponds to the NAAQS for each criteria 
pollutant)25, citizens are given the opportunity to take 
appropriate steps to avoid exposures of concern. This use of the PSI 
could be expanded to provide more specific health information for 
O3 concentrations

[[Page 38874]]

close to the level of the primary standard. Given the continuum of 
risks associated with exposure to O3, this information, 
while perhaps of interest to all citizens, would be particularly useful 
to those individuals who are extremely sensitive to relatively low 
O3 concentrations. As an example, the proposal mentioned the 
possibility of expanding the PSI to include two new descriptive 
categories in the Index, one including concentrations within a range 
somewhat below the level of the new primary standard (with a possible 
descriptor of ``moderately good''), the other including concentrations 
within a range somewhat above the level of the standard (with a 
possible descriptor of ``moderately unhealthful''). Such an approach 
could better reflect the increased understanding of health effects 
associated with O3 exposure developed during this review, 
and would be consistent with the recommendation of a number of CASAC 
panel members ``that an expanded air pollution warning system be 
initiated so that sensitive individuals can take appropriate 'exposure 
avoidance' behavior'' (Wolff, 1995b).
---------------------------------------------------------------------------

    24 For a discussion of these programs, see the proposal.
    25 Currently, a PSI value of 100 for O3 corresponds 
to an ambient concentration of 0.12 ppm, averaged over 1 hour.
---------------------------------------------------------------------------

    The proposal also discussed the use of forecasting in combination 
with this expanded use of the PSI. For a health advisory system to be 
effective, citizens need to be notified as early as possible to be able 
to avoid exposures of concern. The notice indicated that if the current 
1-hour primary NAAQS for O3 is replaced with an 8-hour 
standard, there would clearly be increased value in using forecasted 
O3 concentrations in providing cautionary statements to the 
public. Currently, when a health advisory indicates that the 1-hour 
O3 PSI value of 100 has been exceeded, citizens generally 
have time to avoid exposures of concern because O3 levels 
tend to remain elevated for several hours during the day. With the new 
8-hour standard, however, this would likely not be the case, since by 
the time a PSI value is reported, the potential for prolonged exposures 
of concern would likely have passed for that day. Forecasting 8-hour 
maximum O3 concentrations would facilitate the risk-
reduction function of the PSI by giving citizens more time to limit or 
avoid exposures of concern.
    The EPA did not formally propose revisions to the PSI in the 
proposal. Instead, the Administrator requested comment, and indicated 
that the Agency might propose revisions to the PSI in conjunction with 
future proposals associated with the implementation of a revised NAAQS.
    The EPA received a large number of comments from a wide variety of 
commenters on the usefulness of both an expanded health advisory system 
and the forecasting of 8-hour ambient O3 concentrations. 
Commenters representing State and local agencies, business and industry 
associations, as well as environmental associations overwhelmingly 
endorsed the use of an expanded public health advisory system and many 
noted the importance of forecasting 8-hour O3 concentrations 
in conjunction with the PSI, while recognizing a number of issues that 
would need to be addressed.
    Comments from environmental associations endorsed increasing the 
specificity of warnings with regard to the health effects that could 
occur as a result of exposure, and noted that citizens are capable of 
dealing with complex information. These commenters also took exception 
to describing O3 levels around the level of the standard 
that have been shown to result in decreased lung function and increased 
respiratory symptoms, as ``moderately good,'' stating that this 
descriptor is misleading and might not be heeded by people who could, 
if they fully understood the nature of the health risk, take action to 
minimize their exposures. Other commenters felt that the descriptors 
``moderately good'' and ``moderately unhealthful'' were unnecessarily 
confusing.
    Industry commenters were uniformly supportive of enhancing the risk 
reduction function of the PSI by issuing health advisories with 
specific health information at and above the level of the standard. 
Several industry commenters also recommended that the function of the 
PSI be combined with the function of an O3 action system, 
which would recommend voluntary actions to reduce ambient O3 
concentrations when the level of the standard is forecasted to be 
exceeded. This would result in a system that not only could provide 
accurate health effects information specific to the members of the 
population likely to experience effects, but also could help prevent 
exposures to levels of O3 at or above the level of the 
standard.
    Commenters from State and local air pollution control authorities 
strongly endorsed expanding the use of the PSI and the utilization of 
forecasted 8-hour O3 concentrations. These commenters 
encouraged EPA to develop any such approaches to revise the PSI in 
consultation with State and local agencies, specifically in the areas 
of sharing real-time O3 monitoring data among neighboring 
States, risk communication with the public, and coordination of a 
national program. States also expressed the need for flexibility in the 
implementation of such approaches and for guidance from EPA on 
technical aspects such as forecasting.
    The EPA will take all of these comments into consideration when 
developing a proposal to revise the PSI (40 CFR 58.50) for 
O3. The EPA plans to propose these revisions, as well as 
revisions to the significant harm level program (40 CFR 51.16), at a 
later date.

III. Rationale for the Secondary O3 Standard

A. Introduction

    1. Overview. This notice presents the Administrator's final 
decision regarding the need to revise the current secondary 
O3 standard, and more specifically, to replace the existing 
1-hour, 0.12 ppm O3 secondary NAAQS with a secondary 
standard equal in form, level, and averaging time to the new 8-hour, 
0.08 ppm primary standard. This decision is based on a thorough review 
of the scientific information on vegetation effects associated with 
exposure to ambient levels of O3 as assessed in the Criteria 
Document. This decision also takes into account:
    (1) Staff Paper assessments of the most policy-relevant information 
in the Criteria Document and staff analyses of air quality, vegetation 
exposure and risk, and economic values presented in the Staff Paper, 
upon which staff recommendations for a new O3 secondary 
standard were based.
    (2) Consideration of the degree of protection to vegetation 
potentially afforded by the new 8-hour, 0.08 ppm primary standard 
compared to alternative secondary standards.
    (3) CASAC advice and recommendations as reflected in discussion of 
drafts of the Criteria Document and Staff Paper at public meetings, in 
separate written comments, and in CASAC's letter to the Administrator 
(Wolff, 1996).
    (4) Public comments received during development of these documents 
either in conjunction with CASAC meetings or separately.
    (5) Extensive public comments received on the proposed decision 
regarding the secondary O3 standard.
After taking this information into account and for the reasons 
discussed in this Unit, the Administrator concludes that revisions to 
the current secondary standard are appropriate at this time to provide 
increased protection against adverse effects to public welfare, and 
that it is appropriate to set the new secondary standard identical to 
the new primary standard.
    This review has focused on O3 effects on vegetation 
since these public welfare effects are of most concern at O3

[[Page 38875]]

concentrations typically occurring in the United States. By affecting 
commercial crops and natural vegetation, O3 may also 
indirectly affect natural ecosystem components such as soils, water, 
animals, and wildlife. Based on the scientific literature assessed in 
the Criteria Document, the Administrator believes it is reasonable to 
conclude that a secondary standard that protects the public welfare 
categories of commercial crops and natural vegetation from known or 
anticipated adverse effects would also afford increased protection to 
these other related public welfare categories. With regard to 
O3 effects on manmade materials and deterioration of 
property, the scientific literature assessed in the Criteria Document 
contains little new information since the last review. Accordingly, EPA 
again concludes for the reasons set forth in 1993 (58 FR 13008, March 
9, 1993) that O3-related effects on materials do not provide 
a basis for selecting an averaging time and level for a secondary 
standard. In addition, since the effects of O3 on personal 
comfort and well-being (e.g., nose and throat irritation, chest 
discomfort, and cough) have been accounted for in the review of the 
primary standard, these effects are not considered in this review of 
the secondary standard.
    The vegetation effects information, exposure and risk assessment, 
and economic analyses presented in the Staff Paper and proposal are 
briefly outlined in the remainder of Unit III.A. of this preamble. The 
key issues raised in public comments with regard to: Whether revisions 
to the current secondary standard are requisite to protect public 
welfare from adverse effects and the specific elements of a revised 
secondary standard are discussed in Unit III.B. along with the 
Administrator's rationale for concluding that it is appropriate to 
revise the current secondary standard to be identical to the new 
primary standard.
    2. Vegetation effects information. Exposures to O3 have 
been associated quantitatively and qualitatively with a wide range of 
vegetation effects such as visible foliar injury, growth reductions and 
yield loss in annual crops, growth reductions in tree seedlings and 
mature trees, and effects that can have impacts at the forest stand and 
ecosystem level. Summarized below are key findings for each of the 
above effects categories that are discussed in more detail in the 
Criteria Document, Staff Paper, and proposal.
    Visible foliar injury can represent a direct loss of the intended 
use of the plant, ranging from reduced yield and/or marketability for 
some agricultural species to impairment of the aesthetic value of urban 
ornamental species. On a larger scale, foliar injury is occurring on 
native vegetation in national parks, forests, and wilderness areas, and 
may be degrading the aesthetic quality of the natural landscape, a 
resource important to public welfare.
    Ozone can interfere with carbon gain (photosynthesis) and 
allocation of carbon with or without the presence of visible foliar 
injury. As a result of decreased carbohydrate availability, remaining 
carbohydrates may be allocated to sites of injured tissue or employed 
in other repair or compensatory processes, thus reducing the 
carbohydrates available for plant growth and/or yield. Growth and yield 
effects of O3 have been well documented for numerous 
species, including commodity crops, fruits and vegetables, and 
seedlings of both coniferous and deciduous tree species.
    Due to a number of differences between seedlings and mature trees 
in their responses to O3 exposures, data from tree seedling 
studies cannot, at this time, be extrapolated to quantify responses to 
O3 in mature trees. However, long-term observational studies 
of mature trees have shown growth reductions in the presence of 
elevated O3 concentrations. Where these growth reductions 
are not attributed to O3 alone, due to the presence of many 
other environmental variables, it has been reported that O3 
is a significant contributor that potentially exacerbates the effects 
of other environmental stresses (e.g., pests). In addition, studies 
show that sensitivity to O3 with respect to visible foliar 
injury and growth and yield effects can vary significantly within and 
between species for both crops and trees.
    Growth reductions can indicate that plant vigor is being 
compromised such that the plant can no longer compete effectively for 
essential nutrients, water, light, and space. When many O3-
sensitive individuals make up a population, the whole population may be 
affected. Changes occurring within sensitive populations, or stands, if 
they are severe enough, ultimately can change community and ecosystem 
structure. Structural changes that alter the ecosystem functions of 
energy flow and nutrient cycling can alter ecosystem succession.
    In the CASAC closure letter, all CASAC panel members agreed that 
``damage is occurring to vegetation and natural resources at 
concentrations below the present 1-hour national ambient air quality 
standard (NAAQS) of 0.12 ppm,'' and the vegetation experts agreed that 
``plants appear to be more sensitive to O3 than humans'' 
(Wolff, 1996). Further, the CASAC panel agreed ``that a secondary 
NAAQS, more stringent than the present primary standard, was necessary 
to protect vegetation from O3'' (Wolff, 1996). The 
Administrator concurred in the proposal with the unanimous view of 
CASAC that the current standard of 0.12 ppm, 1-hour average, does not 
provide adequate protection to vegetation from the adverse effects of 
O3, based on the following specific observations that were 
taken from key studies and other biological effects information 
reported in the O3 Criteria Document and Staff Paper:
    (1) O3 concentrations  0.10 ppm can be 
phytotoxic to a large number of plant species, and can produce acute 
foliar injury responses and reduced crop yield and biomass production.
    (2) O3 concentrations within the range of 0.05 to 0.10 
ppm have the potential over a longer duration of creating chronic 
stress on vegetation that can result in reduced plant growth and yield, 
shifts in competitive advantages in mixed populations, decreased vigor 
leading to diminished resistance to pest and pathogens, and injury from 
other environmental stresses. Some sensitive species can experience 
foliar injury and growth and yield effects even when concentrations 
never exceed 0.08 ppm.
    The Administrator further concluded that the available scientific 
information supports the conclusion that a cumulative seasonal exposure 
index, such as the proposed SUM06 index,26 is more 
biologically relevant than a single event or mean index.
---------------------------------------------------------------------------

    26 The SUM06 exposure index cumulates over a given time period 
and diurnal window all hourly O3 concentrations greater 
than or equal to 0.06 ppm.
---------------------------------------------------------------------------

    3. Vegetation exposure and risk analyses. In reaching a judgment in 
the proposal as to a standard requisite to protect crops and vegetation 
against the adverse effects of O3, the Administrator took 
into account several additional considerations including the extent of 
exposure of O3-sensitive species, potential risks of adverse 
effects to such species, and monetized and nonmonetized categories of 
increased vegetation protection associated with reductions in 
O3 exposures. In so doing, the Administrator recognized that 
markedly improved air quality, and thus significant reductions in 
O3 exposures would result from attainment of the alternative 
0.08 ppm, 8-hour primary standards within the range of 1- and 5-
expected exceedance forms. Thus, as a matter of policy, the Agency 
estimated the increased protection from O3-related

[[Page 38876]]

effects on vegetation associated with attainment of alternative 8-hour, 
0.08 ppm primary standards, and then considered the incremental 
protection associated with attainment of a seasonal secondary standard.
    The ability of EPA to characterize O3 air quality in 
rural and remote sites was limited by the available rural O3 
monitoring network. Therefore, EPA conducted national analyses using 
geographic information systems (GIS) and data from existing air quality 
monitoring sites to estimate seasonal O3 air quality for the 
year 1990, in terms of the 3-month, 12-hour, SUM06 exposure index. The 
year 1990 was selected because it was a fairly typical year in terms of 
O3 air quality. The estimated 1990 air quality was then used 
as a baseline from which to roll back O3 concentrations to 
project O3 air quality that would be expected to occur when 
alternative standards were just attained.
    The regulatory scenarios examined included just attaining the 
existing 1-hour secondary standard, alternative 8-hour primary 
standards in the range of 0.07 to 0.09 ppm, including standards set at 
0.08 ppm, with 1- and 5-expected-exceedance forms, and a range of 
seasonal standards using the SUM06 index, based on a single year of 
data. Estimates of air quality associated with alternative 8-hour 
primary standards with 1- and 5-expected-exceedance forms were used to 
roughly bound air quality estimates for 8-hour standards with 
concentration-based forms ranging from the annual second- to the fifth-
highest concentration-based forms, and including the proposed third-
highest concentration-based form.
    By comparing these projected air quality scenarios for alternative 
standards with maps showing the growing regions for O3-
sensitive crops and tree seedling species, estimates of exposures of 
concern and risks of adverse effects for various species were developed 
for alternative standards. Taking into account the body of information 
concerning O3 effects on vegetation, as presented in the 
Criteria Document and Staff Paper and summarized in the proposal, EPA 
considered both quantifiable risks (when exposure-response functions 
were available) as well as those risks that could only be qualitatively 
characterized.
    The Administrator concluded in the proposal that attaining a 8-
hour, 0.08 ppm primary standard within the range of forms under 
consideration would provide substantially improved protection of 
vegetation from seasonal O3 exposures of concern. The 
Administrator recognized, however, that some areas may continue to have 
elevated seasonal exposures, including forested park lands and other 
natural areas and Class I areas that are federally mandated to preserve 
certain air quality related values.
    In its discussions of uncertainties, described in the proposal, the 
CASAC Panel members expressed concerns about the use of the GIS 
methodology to project national O3 air quality and exposures 
of O3-sensitive species. As is the case with other analytic 
methods (e.g., Krieging, inverse distance weighting), the GIS 
methodology contains numerous assumptions and uncertainties, and 
incorporates various databases each with their own set of 
uncertainties. As noted in the Staff Paper and proposal, the EPA and 
CASAC recognized that the uncertainties in exposure and risk estimates 
derived from the GIS methodology are large and unquantifiable, but that 
the method provides useful information that is appropriate to consider 
in comparing the relative protection afforded by alternative standards. 
Further, EPA noted in the Staff Paper and proposal that the GIS-
generated air quality estimates compare reasonably well with the 
limited available O3 monitoring data. In taking the results 
from these analyses into account, the Administrator recognized these 
inherent limitations and primarily considered the comparative results 
in assessing the degree of protection afforded by alternative 
standards.
    While the analyses discussed above indicated that an 8-hour, 0.08 
ppm primary standard within the range of alternatives considered, would 
provide increased protection for commercial and natural vegetation, it 
remained uncertain as to the extent to which air quality improvements 
designed to reduce 8-hour O3 concentrations would reduce 
O3 exposures measured by a seasonal SUM06 index. To further 
explore this question, EPA also examined the design values for 
alternative 8-hour, 0.08 ppm standards, within the range of 1- and 5-
expected exceedances, averaged over 3 years, and a 3-month, 12-hour 
SUM06 standard for 581 counties (those having sufficient monitoring 
data for the period 1991 - 1993). As discussed in the Staff Paper and 
proposal, this analysis revealed that almost all areas that are within 
or above a SUM06 range of 25-38 ppm-hours would also have an 8-hour 
daily maximum design value of greater than 0.08 ppm. Thus, in those 
areas in which air quality monitoring is being conducted, areas that 
would likely be of most concern for effects on vegetation, as measured 
by the SUM06 exposure index, would also be addressed by an 8-hour 
primary standard set at a 0.08 ppm level.
    4. Monetized estimates of vegetation protection. As discussed in 
section VII.F. of the Staff Paper and in the proposal, EPA developed 
monetized estimates of increased protection associated with several 
alternative standards for economically important commodity crops 
nation-wide27 and for fruit and vegetable crops in 
California.28 These analyses were based on the GIS-generated 
projections of O3 air quality for various alternative 
standards. Monetized estimates of increased protection could not be 
developed for other important categories of vegetation, such as urban 
ornamentals, Class I areas, and commercial and other forests because of 
a lack of available concentration-response functions and appropriate 
economic valuation models. The available data suggested, however, that 
reductions in ambient O3 concentrations resulting from 
attainment of alternative standards would confer increased protection 
for these categories as well by reducing biomass loss, protecting 
functional, aesthetic, and existing values, and by preserving 
biodiversity and native habitats.
---------------------------------------------------------------------------

    27 Including 15 species, representing approximately 75% of the 
U.S. sales of agricultural crops, evaluated in the National Crop 
Loss Assessment Network (NCLAN) studies undertaken in the early to 
mid-1980's, which provide the largest, most uniform database on the 
effects of O3 on agricultural crop species.
    28 These fruit and vegetable crops constitute approximately 50% 
of the Nation's fruits and vegetable markets.
---------------------------------------------------------------------------

    As summarized in the proposal, most of the monetized estimates of 
increased protection would accrue from attainment of an 8-hour, 0.08 
ppm primary standard, with a smaller incremental improvement obtained 
by the addition of a seasonal secondary standard. In contrast, the 
incremental protection obtained from the addition of a seasonal 
secondary standard would be considerably more significant when compared 
to an alternative 8-hour primary standard at a level of 0.09 ppm.

B. Need for Revision of the Current Secondary Standard

    Based on the above considerations and the rationale in the 
proposal, the Administrator proposed and sought comment on two 
alternative standards, either of which in her judgment would be 
appropriate to protect public welfare from known or anticipated adverse 
effects given the available scientific knowledge. The two alternatives 
were setting the revised secondary standard

[[Page 38877]]

identical to the proposed 8-hour, 0.08 ppm primary standard, or 
establishing a 3-month, 12-hour, SUM06 seasonal secondary standard at 
the level of 25 ppm-hours. The Administrator recognized that it would 
be a reasonable policy choice to set the revised secondary standard 
identical to an 0.08, 8-hour ppm primary standard, but also recognized 
that a SUM06 seasonal standard is more biologically relevant and, 
therefore, was also appropriate to consider.
    In reaching her final decision on a revised secondary standard, the 
Administrator has taken into account several factors. First, she again 
concludes based on information presented in the Criteria Document and 
Staff Paper, and summarized in the proposal and in this preamble, that 
the existing secondary standard does not provide adequate protection 
for vegetation against the adverse welfare effects of O3.
    Second, she has considered the comments made by the CASAC Panel 
members during their reviews of these documents and in CASAC's closure 
letter, ``that a secondary NAAQS, more stringent than the present 
primary standard, was necessary to protect vegetation from 
O3'' (Wolff, 1996). These statements provide strong support 
to the Administrator's judgment that the body of scientific evidence on 
O3 effects on vegetation provides sufficient and compelling 
evidence that the current secondary standard is not adequately 
protective and should be revised.
    Third, the Administrator recognizes that significant uncertainties 
remain with respect to exposure dynamics, air quality relationships, 
and estimates of increased vegetation protection which are important 
factors in selecting an appropriate secondary standard, as described 
more fully in the Criteria Document, Staff Paper and proposal. The 
CASAC closure letter highlighted key uncertainties that hampered the 
Panel's ability to make any recommendations as to an appropriate form 
or level for a secondary standard that would be protective against 
adverse effects on vegetation from exposure to ambient levels of 
O3. The Panel stated that ``agreement on the level and form 
of such a standard is still elusive'' and ``***there remain important 
limitations to our understanding of the extent of the response of 
vegetation to O3 under field conditions'' (Wolff, 1996). 
These uncertainties are largely a result of inadequate rural and remote 
O3 air quality data that would allow with greater certainty 
determination of the relationships between O3-related 
effects being observed in the field and ambient O3 
exposures. Nevertheless, the alternative standards proposed by the 
Administrator are consistent with the range of views expressed by the 
CASAC panel members, and CASAC recognized that choosing between the two 
alternatives is a policy decision that cannot be based solely on 
science (Wolff, 1996).
    Fourth, the Administrator recognized that just attaining the 8-
hour, 0.08 ppm, 1- and 5-expected exceedance alternatives results in 
markedly improved air quality when compared to just attaining the 
existing secondary standard, with only slight improvements associated 
with going from a 5- to 1-expected exceedance form.
    Fifth, the Administrator has carefully considered the information 
and views provided in the public comments. Though these comments 
yielded no new scientific information relevant to choosing between the 
two alternative proposed standards, many commenters repeated the 
CASAC's concerns over the significant uncertainties remaining in the 
database. Many of these commenters expressed the view that EPA should 
wait to set a seasonal secondary standard until better rural air 
quality data were available, which would allow for better 
characterization of the magnitude of improvements in public welfare 
protection likely to be afforded by such a standard compared to a 
revised primary standard.
    In sharp contrast, other commenters expressed the view that the 
available data were sufficient to demonstrate a need to set a seasonal 
secondary standard to protect vegetation against the adverse effects of 
O3, and many such commenters recommended the proposed SUM06 
form for such a standard. A significant number of these commenters also 
made recommendations on the appropriate level for a seasonal SUM06, 
generally recommending levels lower than the proposed 25 ppm-hours, 
ranging from 8 to 20 ppm-hours. The key source frequently cited in 
support of these recommendations is an article by Heck and Cowling 
(1997) which summarizes the outcome of a consensus-building workshop 
sponsored by the Southern Oxidant Study group on the secondary standard 
held in January 1996.
    This workshop was attended by 16 scientists with backgrounds in 
agricultural, managed forest, natural systems, and air quality, all of 
whom are leaders in their fields and whose research formed the basis of 
much of the research examined in the Criteria Document. These 
scientists expressed their judgements on what standard level(s) would 
provide vegetation with adequate protection from O3-related 
adverse effects.
    Though the report identified no new data in support of the 
scientists' recommendations, the Administrator believes that the report 
lends important support to the view that the current secondary standard 
is not adequately protective of vegetation. Further, the Administrator 
believes that the report foreshadows the direction of future scientific 
research in this area, the results of which could be important in 
future reviews of the O3 secondary standard.
    As the results of such research become available, EPA will be in a 
better position to characterize rural air quality and the improvements 
in vegetation protection that would result from a seasonal secondary 
standard, and to select a standard level that would provide adequate 
protection for vegetation. However, given the present limits of the 
scientific evidence of O3-related effects and of rural air 
quality data, as discussed in the Criteria Document, Staff Paper, the 
proposal, and by CASAC, the Administrator has decided that it is not 
appropriate to move forward with a seasonal secondary standard at this 
time for the reasons described below. In coming to this conclusion, the 
Administrator specifically considered the significant improvements in 
public welfare protection that are expected to be afforded by the new 
8-hour primary standard, as well as the value of obtaining additional 
information to better characterize O3-related effects on 
vegetation under field conditions.

C. Final Decision on the Secondary Standard

    Based on the scientific evidence, CASAC advice and recommendations, 
comments received on the proposal, and the considerations summarized 
above, the Administrator is replacing the current secondary 
O3 standard with an 8-hour standard, set at a level of 0.08 
ppm, identical in all respects to the new primary standard. The 
Administrator judges that this standard will provide substantially 
improved protection for vegetation from O3-related adverse 
effects as compared to that provided by the current 1-hour, 0.12 ppm 
secondary standard, while allowing time for additional research and the 
development of a more complete rural monitoring network and air quality 
database from which to evaluate the elements of an appropriate seasonal 
secondary standard.
    The decision not to set a seasonal secondary standard at this time 
is based

[[Page 38878]]

in large part on the Administrator's recognition that the exposure, 
risk, and monetized valuation analyses presented in the proposal 
contain substantial uncertainties, resulting in only rough estimates of 
the increased public welfare protection likely to be afforded by each 
of the proposed alternative standards. These uncertainties were 
discussed in the proposal and the Staff Paper and were noted by CASAC 
(Wolff, 1996). In light of these uncertainties, the Administrator has 
decided it is not appropriate at this time to establish a new separate 
seasonal secondary standard given the potentially small incremental 
degree of public welfare protection that such a standard may afford. 
Instead, the Administrator finds it a reasonable policy choice to set a 
new secondary standard identical to the new primary standard, while 
focusing additional research on key areas for consideration in the next 
review of the O3 criteria and standards.
    Continued research on the effects of O3 on vegetation 
under field conditions and on better characterizing the relationship 
between O3 exposure dynamics and plant response will be 
important in the next review because:
    (1) The available biological database highlights the importance of 
cumulative, seasonal exposures as a primary determinant of plant 
responses.
    (2) The association between daily maximum 8-hour O3 
concentrations and plant responses has not been specifically examined 
in field tests.
    (3) The impacts of attaining an 8-hour, 0.08 ppm primary standard 
in upwind urban areas on rural air quality distributions cannot 
currently be characterized with confidence due to limited monitoring 
data and air quality modeling in rural and remote areas.
    Setting the secondary standard equal to the primary standard will 
allow EPA the opportunity to evaluate more specifically the improvement 
in rural air quality and in O3-related vegetation effects 
resulting from measures designed to attain the new primary standard. 
This information in turn will allow for better evaluation of the 
incremental need for a separate seasonal secondary standard in the next 
review of the O3 criteria and standards.
    In the proposal, the Administrator solicited comment on the 
appropriate spatial scale of an expanded rural monitoring network. 
Relatively few comments were received regarding an expanded rural 
monitoring network, but those who did submit comments were generally in 
favor of an expanded network to allow for improved modelling of long-
range transport of O3 and its precursors and for better 
characterization of O3 air quality in rural and remote 
areas. Those comments will serve to inform EPA's development of revised 
air quality surveillance requirements (40 CFR part 58) that will be 
proposed at a later date.
    With respect to the proposed seasonal secondary standard only, the 
proposal sought comment on whether O3 concentrations from 
several monitors should be spatially integrated when determining 
compliance with the standard. Only a few comments were received, with 
some supporting and some opposing spatial integration of O3 
concentrations from several monitors.
    In view of the Administrator's decision to replace the current 
secondary standard with a secondary standard which is identical in 
form, level, and averaging time to the new 8-hour, 0.08 ppm primary 
standard, rather than with a seasonal standard, EPA is not adopting the 
use of spatial averaging for the new secondary standard.
    To decrease some of the uncertainties discussed above and to remedy 
the lack of air quality data in rural and remote areas of commercial or 
ecological importance for vegetation, the Administrator reiterates her 
intention, expressed in the proposal, to expand the rural O3 
monitoring network. The EPA will propose revised O3 air 
quality surveillance requirements (40 CFR part 58) at a later date. The 
EPA is exploring opportunities to work with other Federal agencies to 
develop a coordinated and long-term rural monitoring network.

IV. Other Issues

    Several commenters raised key legal and procedural issues that are 
discussed below. These include: (1) Whether EPA must give consideration 
to costs and similar factors in setting NAAQS; (2) whether EPA erred in 
its selection of a methodology for determining the level of a NAAQS 
that protects public health with an adequate margin of safety; (3) 
whether EPA committed a procedural error by not extending the comment 
period; and (4) whether the 1990 amendments to the Act preclude EPA 
from revising the O3 NAAQS to establish a new 8-hour 
standard. Responses to other legal and procedural issues are included 
in the Response-to-Comments Document.

 A. Cost Considerations

    For more than a quarter of a century, EPA has interpreted section 
109 of the Act as precluding consideration of the economic costs or 
technical feasibility of implementing NAAQS in setting them. As 
indicated in the proposal, a number of judicial decisions have 
confirmed this interpretation.  Natural Resources Defense Council v. 
Administrator, 902 F.2d 962, 972-73 (D.C. Cir. 1990)(PM 
NAAQS)(``PM10''), vacated, in part, dismissed, 921 F.2d 326 (D.C. 
Cir.), certs. dismissed, 498 U.S. 1075, and cert. denied, 498 U.S. 1082 
(1991); Natural Resources Defense Council v. EPA, 824 F.2d 1146, 1157-
59 (D.C. Cir. 1987)(en banc)(CAA section 112 standards for vinyl 
chloride)(``Vinyl Chloride''); American Petroleum Institute v. Costle, 
665 F.2d 1176, 1185-86 (D.C. Cir. 1981)(ozone NAAQS)(``Ozone''), cert. 
denied, 455 U.S. 1034 (1982); Lead Industries Ass'n v. EPA, 647 F.2d 
1130, 1148-51 (D.C. Cir.)(lead NAAQS)(``Lead Industries''), cert. 
denied, 449 U.S. 1042 (1980).
    Some commenters have argued that costs and similar factors should, 
nonetheless, be considered, both in this rulemaking and in the 
rulemaking on proposed revisions to the NAAQS for particulate matter. 
Although most of the commenters' arguments are inconsistent with the 
judicial decisions cited above, several commenters have argued that 
those decisions are not dispositive. For reasons discussed below and in 
the Response-to-Comments Document, EPA disagrees with these comments 
and maintains its longstanding interpretation of the Act as precluding 
consideration of costs and similar factors in setting NAAQS.
    1. Background.  Given the nature of the points raised, a brief 
review of the issue seems useful before addressing the comments. The 
requirement that EPA establish national ambient air quality standards 
for certain pollutants, to be implemented by the States, was enacted in 
1970 as part of a set of comprehensive amendments that established the 
basic framework for Federal, State, and local air pollution control. 
When EPA promulgated the original NAAQS in 1971, its first 
Administrator, William D. Ruckelshaus, concluded that costs and similar 
factors could not be considered in that decision.29 This 
conclusion was not challenged in litigation on the original NAAQS. It 
has been confirmed since then, however, by every judicial decision that 
has considered the issue.
---------------------------------------------------------------------------

    29 36 FR 8186, Apr. 30, 1971. EPA has maintained this 
interpretation consistently since then.
---------------------------------------------------------------------------

    As discussed below, EPA's interpretation rests primarily on the 
language, structure, and legislative history of the statutory scheme 
adopted in 1970. It is also supported by the judicial decisions cited 
above, as well as by legislative developments since 1970 that reaffirm 
Congress' original approach to the issue.

[[Page 38879]]

    Without cataloguing all relevant aspects of the 1970 amendments and 
their legislative history, several basic points should be noted. Under 
section 109(b) of the Act, NAAQS are to be ``based on'' the air quality 
criteria issued under section 108. Under section 108(a)(2), the kind of 
information EPA is required to include in criteria documents is limited 
to information about health and welfare effects ``which may be expected 
from the presence of [a] pollutant in the ambient air ***.'' There is 
no mention of the costs or difficulty of implementing the NAAQS, nor of 
``effects'' that might result from implementing the NAAQS (as opposed 
to effects of pollution in the air).30 By contrast, Congress 
explicitly provided for consideration of costs and similar factors in 
decisions under other sections of the Act.31 Moreover, 
States were permitted to consider economic and technological 
feasibility in developing plans to implement the NAAQS to the extent 
such consideration did not interfere with meeting statutory deadlines 
for attainment of the standards.32 Finally, the legislative 
history indicated that Congress had considered the issue and had 
deliberately chosen to mandate NAAQS that would protect health 
regardless of concerns about feasibility.33
---------------------------------------------------------------------------

    30 That consideration of such factors was not intended in NAAQS 
decisions is also supported by section 109(a)(1). For pollutants for 
which air quality criteria had been issued prior to the 1970 
amendments, that provision required EPA to propose NAAQS within 30 
days after enactment and to take final action 90 days later. The 
criteria issued previously did not include information on costs and 
similar factors, and it would have been difficult if not impossible 
for EPA to supplement them in time to include meaningful 
consideration of such factors in NAAQS proposed 30 days after 
enactment.
    31 See, e.g., sections 110(e)(1), 111(a)(1), 231(b) (1970 Act); 
see also, e.g., sections 113(d)(4)(C)(ii), 125(a)(3), 202(a)(3)(C), 
317 (1977 Act).
    32 Union Electric Co. v. EPA, 427 U.S. 246, 257-58 (1976).
    33 The Senate report on the 1970 amendments stated: ``In the 
Committee discussions, considerable concern was expressed regarding 
the use of the concept of technical feasibility as the basis of 
ambient air standards. The Committee determined that (1) the health 
of people is more important than the question of whether the early 
achievement of ambient air quality standards protective of health is 
technically feasible; and, (2) the growth of pollution load in many 
areas, even with application of available technology, would still be 
deleterious to public health.''
    ``Therefore, the Committee determined that existing sources of 
pollutants either should meet the standard of the law or be closed 
down ***.''
    S. Rep. No. 91-1196, at 2-3 (1970).
---------------------------------------------------------------------------

    The first judicial decision on the issue came in the Lead 
Industries case. An industry petitioner argued that EPA should have 
considered economic and technological feasibility in allowing a 
``margin of safety'' in setting primary standards for lead. Based on a 
detailed review of the language, structure, and legislative history of 
the statutory scheme, the U.S. Court of Appeals for the District of 
Columbia Circuit concluded that:
    This argument is totally without merit. [The petitioner] is 
unable to point to anything in either the language of the Act or its 
legislative history that offers any support for its claim ***. To 
the contrary, the statute and its legislative history make clear 
that economic considerations play no part in the promulgation of 
ambient air quality standards under section 109.

647 F.2d at 1148.
    The Court cited a number of reasons for this conclusion. Id. at 
1148-50. Among other things, it noted the contrast between section 
109(b) and other provisions in which Congress had explicitly provided 
for consideration of economic and technological feasibility, as well as 
the requirement that NAAQS be based on air quality criteria defined 
without reference to such factors. Id. at 1148-49 & n.37. The Court 
also noted that, in developing plans to implement NAAQS, States may 
consider economic and technological feasibility only to the extent that 
this does not interfere with meeting the statutory deadlines for 
attainment of the standards; and that EPA may not consider such factors 
at all in deciding whether to approve State implementation plans. Id. 
at 1149 n.37 (citing Union Electric Co. v. EPA, 427 U.S. 246, 257-58, 
266 (1976)).34
---------------------------------------------------------------------------

    34 These limitations would, of course, make little sense if such 
factors could be considered in setting the NAAQS themselves.
---------------------------------------------------------------------------

    As to the legislative history of the 1970 amendments, the Court 
observed that:

    [T]he absence of any provision requiring consideration of these 
factors was no accident; it was the result of a deliberate decision 
by Congress to subordinate such concerns to the achievement of 
health goals.

Id. at 1149. Citing several leading Supreme Court decisions, as well as 
the Senate report quoted above, the Court noted that Congress had 
intended a drastic change in approach toward the control of air 
pollution in the 1970 amendments and was well aware that sections 108-
110 imposed requirements of a ``technology-forcing'' character. 
Id.35
---------------------------------------------------------------------------

    35 Such requirements `` `are expressly designed to force 
regulated sources to develop pollution control devices that might at 
the time appear to be economically or technologically infeasible.' 
'' Id. (quoting Union Electric Co. v. EPA, 427 U.S. at 257).
---------------------------------------------------------------------------

    The Court also noted that Congress had already acted, in further 
amendments adopted in 1977, to relieve some of the burdens imposed by 
the 1970 amendments. Id. at 1150 n.38. Observing that Congress had, 
however, declined to amend section 109(b) to provide for consideration 
of costs and similar factors as requested by industrial interests, id. 
n.39, the Court concluded:

    A policy choice such as this is one which only Congress, not the 
courts and not EPA, can make. Indeed, the debates on the [1970 
amendments] indicate that Congress was quite conscious of this 
fact***.

    *** [I]f there is a problem with the economic or technological 
feasibility of the lead standards, [the petitioner], or any other 
party affected by the standards, must take its case to Congress, the 
only institution with the authority to remedy the problem.

Id. at 1150.
    After the decision in Lead Industries, Supreme Court review was 
sought on the question whether costs and similar factors could be 
considered in setting NAAQS, among other issues. The Supreme Court 
declined to review the decision. Lead Industries Ass'n v. EPA, 449 U.S. 
1042 (1980). The subsequent decisions in Ozone, Vinyl Chloride, and 
PM10, cited above, strongly reaffirmed the interpretation 
adopted in Lead Industries.36 Supreme Court review of the 
Ozone and PM10 decisions was sought but denied. American 
Petroleum Institute v. Gorsuch, 455 U.S. 1034 (1984); American Iron and 
Steel Institute v. EPA, 498 U.S. 1082 (1991).
---------------------------------------------------------------------------

    36 In the PM10 case, for example, the Court 
considered an argument that EPA should have considered potential 
health consequences of unemployment that might result from revision 
of the primary NAAQS for PM:
    ``This claim is entirely without merit. In three previous cases, 
this court has emphatically stated that section 109 does not permit 
EPA to consider such costs in promulgating national ambient air 
quality standards ***. It is only health effects relating to 
pollutants in the air that EPA may consider . *** Consideration of 
costs associated with alleged health risks from unemployment would 
be flatly inconsistent with the statute, legislative history and 
case law on this point.''
    902 F.2d at 973 (emphasis in original; citations omitted).
---------------------------------------------------------------------------

    The Lead Industries opinion focused largely, though not 
exclusively, on the 1970 amendments and their legislative history. 
Perhaps as a result, it did not canvass all the factors that, in fact, 
supported its conclusions at the time. For example, when Congress 
enacted major amendments to the Act in 1977, it was clearly aware that 
some areas of the country had experienced difficulty in attempting to 
attain some of the NAAQS.37 It was also aware that there 
might be no health-effects thresholds for the pollutants involved, and 
that significant uncertainties are inherent in setting health-based 
standards under the Act.38 In response, Congress made

[[Page 38880]]

significant changes in the provisions for implementation of the NAAQS, 
including changes intended to ease the burdens of attainment. It also 
amended sections 108 and 109 in several ways; for example, by requiring 
periodic review and, if appropriate, revision of air quality criteria 
and NAAQS and by establishing a special scientific advisory committee 
(CASAC) to advise EPA on such reviews. Notably, Congress recognized 
that implementation of NAAQS could cause ``adverse public health, 
welfare, social, economic, or energy effects'' and charged CASAC with 
advising EPA on such matters.39 Yet it made no changes in 
sections 109(b) or 108(a)(2); that is, in the substantive criteria for 
setting or revising NAAQS. In other words, Congress chose to address 
economic and other difficulties associated with attainment of the NAAQS 
by adjusting the scheme for their implementation, rather than by 
changing the instructions for setting them.40
---------------------------------------------------------------------------

    37 See, e.g., H.R. Rep. No. 95-294, at 207-17 (l977).
    38 See, e.g., id. at 110-12; id. at 43-51.
    39 Section 109(d)(2)(C)(iv). Some commenters have argued that 
this provision requires EPA to consider such effects in setting 
NAAQS. From the language and structure of section 109(d), however, 
it is clear that CASAC's responsibility to advise on these factors 
is separate from its responsibility to review and recommend revision 
of air quality criteria and NAAQS, and that the advice pertains to 
the implementation of NAAQS rather than to setting them. The 
legislative history confirms this view, indicating that the advice 
was intended for the benefit of the States and Congress. See H.R. 
Rep. No. 95-294, at 183 (1977).
    40 The 1977 amendments also required EPA to prepare economic 
impact assessments for specified actions but limited the requirement 
to non-health-based standards, excluding decisions under sections 
109 and 112. Section 317; H.R. Rep. No. 95-294, at 51-52 (1977). In 
this and other respects, Congress continued the approach it took in 
the l970 amendments, making careful choices as to when consideration 
of costs and similar factors would be required and giving paramount 
priority to protection of health. See 123 Cong. Rec. H8993 (daily 
ed. Aug. 4, 1977) (Clean Air Conference Report (1977); Statement of 
Intent; Clarification of Select Provisions), reprinted in 3 Senate 
Committee on Environment and Public Works, 95th Cong., A Legislative 
History of the Clean Air Act Amendments of 1977, at 319 (1978).
---------------------------------------------------------------------------

    Congress enacted major amendments to the Act again in 1990, well 
after the Lead Industries and Ozone decisions that interpreted section 
109 as precluding consideration of costs in NAAQS 
decisions.41 In doing so, Congress was clearly aware of 
intervening developments such as EPA's decision to revise the PM NAAQS 
in 1987--the result of an elaborate review in which the Administrator 
strongly underscored the scientific uncertainties 
involved42--and the Vinyl Chloride case drawing a sharp 
distinction between sections 109 and 112 with regard to consideration 
of costs and similar factors.43 Indeed, the legislative 
history of the 1990 amendments reflects Congress' understanding that 
primary NAAQS were to be based on protection of health ``without regard 
to the economic or technical feasibility of attainment.''44 
Again, however, Congress chose to respond to severe, widespread, and 
persistent problems with attaining the NAAQS by adjusting the scheme 
for their implementation rather than by changing the basis for setting 
them. See, e.g., sections 181-192.
---------------------------------------------------------------------------

    41 In the interim, the National Commission on Air Quality had 
also submitted its report to Congress as required by a provision of 
the 1977 amendments. Among other things, the Commission recommended 
that the statutory approach of requiring NAAQS to be set at levels 
necessary to protect public health, without consideration of 
economic factors, be continued without change. National Commission 
on Air Quality, To Breathe Clean Air 55 (1981).]
    42 As the Administrator indicated in EPA's proposal to revise 
the PM standards:
    ``[T]hat review has revealed a highly limited data base--
particularly where quantitative studies are concerned--and a wide 
range of views among qualified professionals about the exact 
pollution levels at which health effects are likely to occur. The 
setting of an `adequate margin of safety' below these levels calls 
for a further judgment--in an area for which the scientific data 
base is even more sparse and uncertain***.''
    ``[L]ong and expert review of public health issues has to date 
revealed no scientific method of assessing exactly what level of 
standards public health requires. The scientific review indicates 
substantial uncertainties concerning the health risks associated 
with lower levels of particulate matter.''
    49 FR 10408, 10409, Mar. 20, l984.
    43 Congress was clearly aware of the 1987 decision to revise the 
PM NAAQS, which among other things involved changing the indicator 
for particulate matter from ``total suspended particulate'' to 
PM10, because it enacted special nonattainment 
provisions, as well as provisions for PSD increments, applicable to 
PM10. Sections 188-190; section 166(f). It was clearly 
aware of the Vinyl Chloride decision because it amended section 112 
in response to that decision, essentially creating a new scheme for 
setting emission standards for hazardous pollutants.
    44 H.R. Rep. No. 101-490, pt. 1, at 145 (1990). See also S. Rep. 
No. 101-228, at 5 (1989).
---------------------------------------------------------------------------

    2. Public comments. As noted previously, a number of commenters 
have argued that costs and similar factors should be considered in 
EPA's final decisions on revision of both the ozone and particulate 
NAAQS. Aside from arguments that are simply inconsistent with the 
judicial decisions cited above, some of the commenters argue that those 
decisions are not dispositive for a variety of reasons. One commenter 
submitted a particularly comprehensive version of this argument in the 
rulemaking on proposed revisions to the particulate NAAQS; the 
following discussion focuses primarily on points raised by that 
commenter, among others.45
---------------------------------------------------------------------------

    45 Additional responses to points raised by this commenter and 
others are included, as appropriate, in the Response-to-Comments 
document.
---------------------------------------------------------------------------

    As a general matter, the commenter acknowledges that Congress 
intended to preclude consideration of economic costs and similar 
factors in setting NAAQS. The commenter argues, however, that this is 
so only when the scientific basis for NAAQS is ``clear and compelling'' 
or ``unambiguous.'' From that premise, the commenter advances three key 
assertions:
    (1) Where non-threshold pollutants are involved and the health 
evidence is ambiguous, section 109 must be interpreted to allow 
consideration of all relevant factors, including the practical 
consequences of EPA's decisions;
    (2) To the extent the judicial decisions cited above are read as 
precluding this, they rest on a faulty analysis that pre-dates and 
cannot survive scrutiny under Chevron, U.S.A. v. Natural Resources 
Defense Council, 467 U.S. 837 (1984);46 and
---------------------------------------------------------------------------

    46 Several other commenters argue that the cited decisions are 
not dispositive because they held only that EPA is not required to 
consider costs and similar factors in setting NAAQS. As discussed 
below in connection with Chevron, however, the decisions clearly 
concluded that Congress intended to preclude consideration of such 
factors, and that EPA is not free to alter that congressional 
choice. Although these conclusions are technically dicta, nothing in 
the Court's opinions suggests that it would have interpreted section 
109 differently had EPA claimed authority to consider costs and 
similar factors in NAAQS decisions. Indeed, the tone of the opinions 
argues to the contrary. See, e.g., PM10, 902 F.2d at 973. 
Cf. Ethyl Corp. v. EPA, 51 F.3d 1053 (D.C. Cir. 1995).
---------------------------------------------------------------------------

    (3) Because EPA has discretion to consider costs and similar 
factors where the health evidence is ambiguous, it must do so in light 
of Executive Order 12866, 58 FR 51735, Oct. 4, 1993, and two recent 
statutes, the Unfunded Mandate Reform Act of 1995, 2 U.S.C. secs. 1501-
1571 (UMRA), and the Small Business Regulatory Enforcement Fairness Act 
of 1996, Pub. L. No. 104-121, 110 Stat. 857 (SBREFA), which in part 
amended the Regulatory Flexibility Act, 5 U.S.C. secs. 601-808.
    EPA believes all three assertions are clearly incorrect. Regarding 
the first point, it should be evident, both from previous NAAQS 
decisions and from the court opinions upholding them, that the 
scientific basis for NAAQS decisions has never pointed clearly and 
unambiguously to a single ``right answer.''47 This is 
inherent in the statutory scheme for the establishment and revision of 
NAAQS, which in effect requires them to be based on the ``latest

[[Page 38881]]

scientific knowledge'' on potential health and welfare effects of the 
pollutant in question. See sections 109(b), 108(a)(2). Although 
advances in science increase our understanding of such effects, they 
also raise new questions. For this reason, the key studies for any 
given decision on revision of a NAAQS are, almost by definition, ``at 
the very `frontiers of scientific knowledge.' ''48 That is, 
studies that call into question the adequacy of a standard are always 
those that go beyond previous studies--by reporting new kinds of 
effects, for example, or effects at lower concentrations than those at 
which effects have been reported previously.
---------------------------------------------------------------------------

    47 See, e.g., Lead Industries, 647 F.2d at 1146-47, 1153-56, 
1160-61, 1167 n.106. In enacting the 1970 amendments, Congress was 
aware that there were gaps in the scientific information available 
then as a basis for establishing the original NAAQS. See, e.g., S. 
Rep. No. 91-1196, at 9-11 (1970). If anything, Congress had an even 
greater understanding of the point when it enacted that 1977 
amendments without changing the substantive criteria for setting 
NAAQS. See H.R. Rep. No. 95-294, at 43-51, 181-82 (1977).
    48 Lead Industries, 647 F.2d at 1147 (quoting Ethyl Corp. v. 
EPA, 541 F.2d 1, 24-27 (D.C. Cir.) (en banc), cert. denied, 426 U.S. 
941 (1976)).
---------------------------------------------------------------------------

    As with pioneering work in other fields, such studies may have a 
variety of strengths and limitations.49 As a result, the 
validity and implications of such studies may be both uncertain and 
highly controversial. Given the precautionary nature of section 
109,50 however, it is precisely these kinds of studies that 
the Administrator must grapple with when advances in science suggest 
that revision of a NAAQS is appropriate.
---------------------------------------------------------------------------

    49 They may have methodological flaws, for example, but 
nonetheless report effects that are of serious medical significance; 
or they may be of impeccable quality but involve effects of 
uncertain significance. Others may involve results that are striking 
but hard to explain in terms of previous knowledge, or results that 
seem plausible and important but are not yet replicated by other 
studies.]
    50 See, e.g., Lead Industries, 647 F.2d at 1155-56; H.R. Rep. 
No. 94-295, at 43-51 (1977).
---------------------------------------------------------------------------

    As a result, the EPA staff typically recommends for consideration, 
and the Administrator may propose for comment, a range of alternatives 
based on what the commenter would call ``ambiguous'' science. In this 
respect, the current reviews of the NAAQS for ozone and particulate 
matter are not unusual and do not differ, for example, from the review 
that led to adoption of the PM10 NAAQS in 1987.51 
Indeed, the NAAQS that were upheld in the Lead Industries, Ozone, and 
PM10 decisions were all based on highly controversial health 
evidence; the Lead Industries decision took note of congressional 
statements recognizing that there may be no thresholds for criteria 
pollutants; and the Ozone and PM10 decisions noted the 
Administrator's findings that clear thresholds could not be identified 
for ozone and particulate matter, respectively.52 Thus, the 
present decisions on revision of the NAAQS for ozone and particulate 
matter cannot be distinguished from those past decisions in terms of 
the nature of the health evidence or pollutants involved.53
---------------------------------------------------------------------------

    51 As previously discussed, the Administrator strongly 
emphasized the uncertainties involved in that review. As a result of 
the uncertainties, he proposed ``relatively broad'' ranges for 
comment, though he focused on lower levels within the ranges as 
providing greater margins of safety against the health risks 
involved. See 49 FR 10408, 10409, Mar. 20, l984.
    52 See, e.g., Lead Industries, 647 F.2d at 1152-53 & n. 43, 
1159-60; Ozone, 665 F.2d at 1185, 1187; PM10, 902 F.2d at 
969-71, 972.
    53 Indeed, the present decisions on the NAAQS for PM and ozone 
are based on some of the best scientific information the Agency has 
ever been able to rely on in NAAQS decision-making. In particular, 
the science underlying these decisions is much more extensive and of 
much better quality than the science underlying the existing NAAQS 
for PM and ozone.
---------------------------------------------------------------------------

    Regarding the second of the commenter's key assertions, EPA 
believes it is clear that the judicial decisions cited above were 
correctly decided and continue to be good law under Chevron. In 
Chevron, the Supreme Court essentially reaffirmed the principle that 
courts must defer to reasonable agency interpretations of the statutes 
they administer where Congress has delegated authority to them to 
elucidate particular statutory provisions. Where the intent of Congress 
on an issue is clear, however, it must be given effect by the agency 
and the courts. See 467 U.S. at 842-45. Thus, the first question on 
review of an agency's interpretation under Chevron is ``whether 
Congress has directly spoken to the precise question at issue.'' If the 
court determines that it has not, the remaining question for the court 
is ``whether the agency's answer is based on a permissible construction 
of the statute.'' 467 U.S. at 842-43 (footnote omitted). In determining 
whether Congress ``had an intention on the precise question at issue,'' 
a court employs ``traditional tools of statutory construction.'' Id. at 
843 n.9.54
---------------------------------------------------------------------------

    54 In practice, analysis of this question is sometimes referred 
to as a ``Chevron step one'' analysis.
---------------------------------------------------------------------------

    In essence, the commenter's argument here is that the Lead 
Industries decision did not address whether Congress had ``spoken 
directly'' to the precise issue posed by the commenter; that is, 
whether section 109 must be interpreted differently for NAAQS decisions 
involving non-threshold pollutants and ``ambiguous'' health evidence. 
The Lead Industries opinion, which pre-dated Chevron, did not pose the 
question in those terms. Its focus, however, was clearly on what 
Congress intended to be the basis for NAAQS decisions, in a context the 
Court understood to involve considerable uncertainty and debate about 
the health evidence, as well as the possibility that there was no 
threshold for health effects of the pollutant.55 In short, 
the health evidence was hardly ``unambiguous,'' yet the Court 
interpreted section 109 as precluding consideration of costs and 
similar factors even in allowing a margin of safety. Nothing in the 
Lead Industries decision or in the subsequent cases suggests in any way 
that section 109 should be interpreted differently based on the nature 
of the pollutants or health evidence involved, and the Court's findings 
on congressional intent admit of no exceptions:
---------------------------------------------------------------------------

    55 See, e.g., 647 F.2d at 1148-51, 1152-53 & n.43, 1160-61.

    [T]he statute and its legislative history make clear that 
economic considerations play no part in the promulgation of ambient 
---------------------------------------------------------------------------
air quality standards under section 109.

647 F.2d at 1148.
    Alternatively, the commenter argues that the Lead Industries case 
decided the issue incorrectly in light of the principles announced 
subsequently in Chevron. In this context, the commenter essentially 
argues that the Lead Industries decision rested on two factors that are 
no longer probative: (1) That there was no indication that Congress 
meant to allow consideration of costs in NAAQS decisions, and (2) that 
Congress specifically provided for such consideration in other sections 
of the Act but not in section 109. On the first point, the commenter 
argues that EPA is free under Chevron to consider costs and similar 
factors (by reinterpreting section 109) unless there is evidence that 
Congress intended to restrict its discretion. As to the second point, 
the commenter argues that similar reasoning was rejected in Vinyl 
Chloride.
    In Vinyl Chloride, however, an en banc decision that post-dated 
Chevron, the Court essentially underscored the point that such issues 
cannot be decided mechanically but must turn, instead, on more 
analytical attention to relevant indicia of congressional intent. See, 
e.g., 824 F.2d at 1157 n.4; id. at 1157-63. With reference to NAAQS 
decisions in particular, the Court concluded that there were concrete 
indications of congressional intent to preclude consideration of costs 
and similar factors; for example, the fact that section 108 
``enumerate[s] specific factors to consider and pointedly exclude[s] 
feasibility.'' 824 F.2d at 1159. In a later case, moreover, the same 
Court held that EPA could not consider certain factors, in decisions 
under section 211(f)(4) of the Act, for reasons exactly parallel to 
those that the commenter criticizes in Lead Industries. See Ethyl Corp. 
v. EPA, 51 F.3d 1053, 1057-63 (D.C. Cir. 1995).

[[Page 38882]]

    Beyond this, the commenter's characterization of the Lead 
Industries decision ignores or discounts much of the key evidence cited 
by the Court, including the language, structure, and legislative 
history of the statutory scheme established in 1970, for its conclusion 
that Congress intended to preclude consideration of costs and similar 
factors in NAAQS decisions.56 As indicated above, the Vinyl 
Chloride and PM10 cases, both of which post-dated Chevron, 
reached the same conclusion.
---------------------------------------------------------------------------

    56 See 647 F.2d at 1148-51. By contrast, the commenter's 
argument that Congress actually intended EPA to consider such 
factors relies heavily on (1) statements made in subsequent 
legislative history, most of which were made in floor debate, that 
sought to justify controversial amendments to establish a different 
program than the NAAQS and did not involve any proposed changes in 
section 109 or related provisions; and (2) statements in early 
judicial decisions involving programs under other statutory 
provisions. In context, EPA believes these and other statements 
cited by the commenter are consistent with and do not alter the 
conclusion that Congress intended to preclude consideration of costs 
and similar factors under section 109.
---------------------------------------------------------------------------

    Moreover, this series of decisions went far beyond mere deference 
to an agency interpretation. As indicated in the Vinyl Chloride case, 
the Lead Industries court found ``clear evidence'' of congressional 
intent, which was to limit the factors EPA may consider under section 
109. 824 F.2d 1159. Consistent with Chevron, these findings were based 
on traditional tools of statutory construction. See id. at 1157-59; 
Lead Industries, 647 F.2d at 1148-51. In terms of the analytical 
framework later established by Chevron, these were Chevron step one 
findings, meaning that the statute spoke directly to the issue and that 
the courts, as well as the agency, must give effect to Congress' intent 
as so ascertained. See 467 U.S. at 842-43.57 Thus, absent a 
more recent legislative enactment overriding that intent, EPA has no 
discretion to alter its longstanding interpretation that consideration 
of costs and similar factors is precluded in NAAQS decisions under 
section 109.58
---------------------------------------------------------------------------

    57 The commenter argues that the post-Chevron cases accepted the 
Lead Industries analysis uncritically rather than re-examining it 
under Chevron. Clearly, this elevates form over substance. It is 
true that neither case referred to Chevron in discussing the point 
at issue. In Vinyl Chloride, however, the Court retraced the steps 
in the Lead Industries analysis in some detail, characterized some 
of the key evidence reviewed in that analysis in terms going beyond 
mere rote repetition (e.g., ``a far clearer statement than anything 
in the present case that Congress considered the alternatives''), 
and used Chevron-like language in discussing the significance of 
that evidence; that is, that it demonstrated congressional intention 
on the point at issue. E.g., 824 F.2d at 1159. Given that the Vinyl 
Chloride case was decided 3 years after Chevron, that it was an en 
banc decision of the D.C. Circuit involving interpretation of 
statutory language very similar to that in Lead Industries, and that 
the Court cited Chevron twice in analyzing the language and history 
of section 112, it seems highly unlikely that the Court was 
unmindful of Chevron principles in concluding that Congress intended 
to preclude consideration of costs under section 109 but not under 
section 112.
    In the PM10 decision, the Court confirmed the sharp 
distinction it had drawn, based on such evidence of congressional 
intent, between sections 109 and 112 in Vinyl Chloride. 902 F.2d at 
972-73. Although discussion of the point was brief and did not 
mention Chevron, the industry petitioner raising the point had cited 
Chevron in arguing that the Lead Industries interpretation was not 
binding, and that EPA's decision on the PM10 standards 
should be reversed on the ground that it rested on a legal position 
that EPA unjustifiably believed was mandated by Congress. Reply 
Brief of the American Iron and Steel Institute at 11 & n.10, Natural 
Resources Defense Council v. Administrator, 902 F.2d 962 (D.C. Cir. 
1990) (Nos. 87-1438 et al.). Thus, Chevron issues were properly 
before the Court and were brought squarely to its attention.
    58 See also 52 FR 24854, July 1, 1987.
---------------------------------------------------------------------------

    As to the commenter's third key assertion, Executive Order 12866 
(58 FR 51735, October 4, 1993) UMRA sections 202 and 205, and the 
Regulatory Flexibility Act (RFA), as amended by SBREFA, do not conflict 
with this interpretation or require a different result. Basically, the 
commenter argues that the Executive Order, UMRA, and the RFA (as 
amended by SBREFA) require agencies to use cost (or similar factors) as 
a decisional criterion in making regulatory decisions, and that this 
modifies the Clean Air Act's directive that EPA is precluded from 
considering costs when setting a NAAQS. The commenter's argument is 
flawed on a number of grounds. First, UMRA and the RFA (as amended by 
SBREFA) do not conflict with section 109 because they do not apply to 
this decision, as discussed in Unit VIII of this preamble. Second, the 
Executive Order and both statutes are quite clear that they do not 
override the substantive provisions in an authorizing statute. Third, 
the commenter's premise that UMRA and the RFA (as amended by SBREFA) 
establish substantive decisional criteria that agencies are required to 
follow is wrong.
    As a matter of law, the Executive Order cannot (and does not 
purport to) override the Clean Air Act. The Executive Order does not 
conflict with section 109 because the requirement that agencies 
``select approaches that maximize net benefits'' does not apply if a 
``statute requires another regulatory approach.'' EO 12866, sec. 
(1)(a), 58 FR 51735, Oct. 4, 1993. More generally, the Executive Order 
provides that agencies are to adhere to its regulatory principles only 
``to the extent permitted by law.'' Id., sec. (1)(b).
    UMRA sections 202 and 205 do not apply to this decision, as 
discussed in Unit VII of this preamble. Even when they do apply to a 
regulatory action, they do not establish decisional criteria that an 
agency must follow, much less override decisional criteria established 
in the statute authorizing the regulatory action. UMRA does not require 
an agency to select any particular alternative. Rather, an agency can 
select an alternative that is not the least costly, most cost-effective 
or least burdensome if the agency explains why, sec. 205(b)(1). Such an 
explanation is not required if the least costly, most cost-effective or 
least burdensome alternative would have been ``inconsistent with law,'' 
sec. 205(b)(2), and the only alternatives that an agency should 
consider are ones that ``achieve[] the objectives of the rule,'' sec. 
205(a). The UMRA Conference Report confirms that UMRA does not override 
the authorizing statute. ``This section [202] does not require the 
preparation of any estimate or analysis if the agency is prohibited by 
law from considering the estimate or analysis in adopting the rule.'' 
141 Cong. Rec. H3063 (daily ed. March 13, 1995).
    The RFA (as amended by SBREFA) also does not apply to this 
decision, as discussed in Unit VII of this preamble. As is the case 
with UMRA, even when the RFA (as amended by SBREFA) does apply to a 
regulatory action, it does not establish decisional criteria that an 
agency must follow, much less override the underlying substantive 
statute. When the RFA was adopted in 1980, Congress made clear that it 
did not alter the substantive standards contained in authorizing 
statutes: ``The requirements of section 603 and 604 of this title [to 
prepare initial and final regulatory flexibility analyses] do not alter 
in any manner standards otherwise applicable by law to agency action.'' 
Section 606 of the RFA. The legislative history further explains that 
section 606 ``succinctly states that this bill does not alter the 
substantive standard contained in underlying statutes which defines the 
agency's mandate.''59 When Congress passed SBREFA in 1996 
and amended parts of the RFA, it did not amend section 606.
---------------------------------------------------------------------------

    59 126 Cong. Rec. 21452, 21455 (1980) (Description of Major 
Issues and Section-By-Section Analysis of Substitute for S. 299).
---------------------------------------------------------------------------

    Even when a regulatory decision is subject to sections 603 and 604 
and an agency is therefore required to analyze alternatives that 
minimize significant economic impacts on small entities, the RFA (as 
amended by SBREFA) does not establish decisional criteria that an 
agency is required to follow. Both section 603 and 604 provide that the

[[Page 38883]]

alternatives an agency should consider are to be ``consistent with the 
stated objectives of applicable statutes.'' Sec. 603 and 604(a)(5). 
Furthermore, although the RFA (as amended by SBREFA) requires agencies 
to consider alternatives that minimize impacts on small entities 
subject to the rules' requirements and to explain their choice of 
regulatory alternatives, it does not require agencies to select such 
alternatives. For these reasons, the RFA (as amended by SBREFA) does 
not conflict with or override the Clean Air Act's preclusion of 
considering costs and similar factors in setting NAAQS.
    3.  Conclusion. In summary, EPA believes that the judicial 
decisions cited above are both correct and dispositive on the question 
of considering costs in setting NAAQS, and that the Agency is not free 
to reinterpret the Act on that question.

B. Margin of Safety

    Several commenters questioned the approach used by the 
Administrator in specifying O3 standards that protect public 
health with an adequate margin of safety. Rather than the integrative 
approach applied by the Administrator, these commenters maintained that 
EPA must employ a two-step process. The line of argument was that the 
Administrator must first determine a ``safe level'' and then apply a 
margin of safety taking into account costs and societal impacts. It was 
argued that this was the only approach that would enable the 
Administrator to reach a reasoned decision on a standard level that 
protects public health against unacceptable risk of harm, such that any 
remaining risk was ``acceptable.'' In effect, these commenters argued 
that the Administrator must adopt the two-step methodology endorsed in 
Vinyl Chloride, 824 F.2d 1146, for setting hazardous air pollutant 
standards under section 112.
    In recognition of the complexities facing the Administrator in 
determining a standard that protects public health with an adequate 
margin of safety, the courts have declined to impose any specific 
requirements on the Administrator's methodological approach. Thus, in 
Lead Industries the court held that the selection of any particular 
approach to providing an adequate margin of safety ``is a policy choice 
of the type Congress specifically left to the Administrator's judgment. 
This court must allow him the discretion to determine which approach 
will best fulfill the goals of the Act.'' 647 F.2d at 1161-62. As a 
result, the Administrator is not limited to any single approach to 
determining an adequate margin of safety and may, in the exercise of 
her judgment, choose an integrative approach, a two-step approach, or 
perhaps some other approach, depending on the particular circumstances 
confronting her in a given NAAQS review.
    With respect to the approach advanced in comment, the 
PM10 case made clear that the two-step process endorsed in 
Vinyl Chloride was necessary because of the need under section 112 of 
the Act to ``sever determinations that must be based solely on health 
considerations from those that may include economic and technical 
considerations.'' 902 F.2d at 973. Because the Administrator may not 
consider cost and technological feasibility under section 109, however, 
the court concluded that ``the rationale for parsing the 
Administrator's determination into two steps is inapposite.'' Id.
    Because such factors as the nature and severity of the health 
effects involved, the size of the sensitive population(s) at risk, the 
types of health information available, and the kind and degree of 
uncertainties that must be addressed will vary from one pollutant to 
another, the most appropriate approach to establishing a NAAQS with an 
adequate margin of safety may be different for each standard under 
review. Thus, no generalized paradigm such as that imbedded in EPA's 
cancer risk policy can substitute for the Administrator's careful and 
reasoned assessment of all relevant health factors in reaching such a 
judgment. As noted above, both Congress and the courts have left to the 
Administrator's discretion the choice of analytical approaches and 
tools, including risk assessments, rather than prescribing a particular 
formula for reaching such determinations. Because of the inherent 
uncertainties that the Administrator must address in margin of safety 
determinations, they are largely judgmental in nature, particularly 
with respect to non-threshold pollutants, and may not be amenable to 
quantification in terms of what risk is ``acceptable'' or any other 
metric. In view of these considerations, the task of the Administrator 
is to select an approach that best takes into account the health 
effects and other information assessed in the air quality criteria for 
the pollutant in question and to apply appropriate and reasoned 
analysis to ensure that the scientific uncertainties are taken into 
account in an appropriate manner.
    In this instance, the Administrator has clearly articulated the 
factors she has considered, the judgments she has had to make in the 
face of uncertain and incomplete information, and alternative views as 
to how such information should be interpreted, in reaching her decision 
on standard specifications that will protect public health with an 
adequate margin of safety. See Unit II of this preamble. Her 
conclusions on these matters are fully supported by the record.

C. Comment Period

    A number of commenters maintained that EPA erred by not extending 
the comment period for the review of the O3 standards by at 
least 60 days. The commenters further maintained there was no 
justification for keeping the O3 standard review on the same 
schedule as the PM NAAQS, since the O3 review is not subject 
to a court-ordered deadline as is PM.
    The EPA believes that there are benefits to reviewing the 
O3 and PM NAAQS on the same schedule, for the reasons set 
forth in the proposal, and that the period available for public comment 
was sufficient. All interested parties have had ample notice that EPA 
intended to complete this review of the O3 standards on an 
expedited basis. The EPA first announced its intention in a March 9, 
1993, Federal Register notice (58 FR 13008) when the Administrator 
announced her commitment to expedite the review in light of new 
scientific evidence of the effects of O3 on human health. In 
a February 3, 1994, Federal Register notice (59 FR 5164), the 
Administrator announced a schedule for completion of the scientific 
assessment and review of the standards, including opportunities for 
public comment. This schedule called for proposal in mid-1996 and a 
final decision as to whether to revise the O3 standard by 
mid-1997. On June 12, 1996, in an advance notice of proposed rulemaking 
(61 FR 29719), the Administrator announced her decision to delay the 
O3 proposal schedule in order to place it on the same 
schedule as the PM standard review. In that notice, she explained her 
rationale for reviewing the O3 and PM NAAQS on the same 
schedule and pointed to the benefits of developing integrated 
implementation strategies. She also provided advance notice of the 
kinds of revisions to the primary and secondary O3 NAAQS 
that she was considering proposing. In effect, the delay of the 
O3 proposal provided interested parties an additional 5 
months to review EPA's assessments of the scientific and technical 
information, as well as staff and CASAC recommendations as to whether 
revisions were appropriate. With this background, EPA believes all 
interested parties had ample opportunity to develop specific

[[Page 38884]]

comments on the O3 proposal during the 89 days allotted for 
public comment.60
---------------------------------------------------------------------------

    60 This comment period reflects an extension of 22 days beyond 
the 67-day comment period originally announced in the proposal.
---------------------------------------------------------------------------

    Another commenter raised a more specific issue in requesting a 60-
day extension of the public comment period. This commenter maintained 
that such an extension was necessary because EPA did not make publicly 
available certain O3 exposure and health risk assessment 
reports and an explanatory memoranda in a timely manner. In response, 
EPA notes that the documents in question were entered into the docket 
on February 12, 1997, and placed on the OAQPS Technology Transfer 
Bulletin Board on February 13, 1997, so that they would have wide 
public circulation. Because this commenter's organization was aware 
that the reports were under preparation and had expressed interest in 
receiving them, copies were sent directly to the responsible staff 
person on February 12, 1997. Given that these reports build on analyses 
and methodologies that were available to the public during the 
scientific phase of the O3 NAAQS review, well in advance of 
the proposal, and that the new analyses and explanatory memorandum were 
only 120 pages in length, EPA believes that this commenter had 
sufficient time to review the material and prepare comments before the 
close of the comment period on March 12, 1997.

D. 1990 Act Amendments

    Contrary to the view expressed in some public comments, EPA 
maintains that the provisions of subpart 2 of Part D of Title I of the 
Clean Air Act, enacted in 1990, do not preclude EPA from revising the 
O3 standard. The provisions of subpart 2 simply do not limit 
EPA's clear authority under section 109 to revise the standard.
    The basic contention of the commenters is that because the 
provisions of subpart 2 are linked to the current 1-hour, 0.12 ppm 
O3 standard, they prohibit EPA from revising the 
O3 standard. These provisions, however, do not lead to such 
a conclusion. Moreover, the view expressed in these comments ignores 
provisions indicating that Congress believed that EPA could revise the 
O3 NAAQS.
    At the outset, it should be noted that Congress expressly 
authorized EPA to revise any ambient air quality standard in section 
109. That section, which requires EPA to review and revise, as 
appropriate, each NAAQS every 5 years, contains no language expressly 
or implicitly prohibiting EPA from revising a NAAQS. If Congress had 
intended to preclude EPA from reviewing and revising a NAAQS, which is 
one of EPA's fundamental functions, Congress would have specifically 
done so. Clearly, Congress knew how to preclude EPA from exercising 
otherwise existing regulatory authority and did so in other instances. 
See section 202(b)(1)(C)(expressly precluding EPA from modifying 
certain motor vehicle standards prior to model year 2004); section 
112(b)(2)(preventing EPA from adding to the list of hazardous air 
pollutants any air pollutants that are listed under section 108(a) 
unless they meet the specific exceptions of section 112(b)(2)); section 
249(e)(3), (f) and section 250(b)(limiting EPA's authority regarding 
certain clean-fuel vehicle programs). No such language was included in 
either section 109 or elsewhere in the Act and no such implication may 
properly be based on the provisions of subpart 2 of Part D of Title I.
    Second, other provisions of the Act expressly contemplate EPA's 
ability to revise any NAAQS, and provide no indication that such 
ability is limited to standards other than those whose implementation 
is the subject of subparts 2, 3 and 4 of Part D. For example, section 
110(a)(2)(H)(i) provides that SIPs are to provide for revisions ``from 
time to time as may be necessary to take account of revisions of such 
national primary or secondary ambient air quality standard ***.'' 
Section 107(d)(1)(A) provides a process for designating areas as 
attainment, nonattainment, or unclassifiable ``after promulgation of a 
new or revised standard for any pollutant under section 109 ***.'' 
Section 172(e) addresses modifications of national primary ambient air 
quality standards. Finally, section 172(a)(1) expressly contemplates 
that EPA may revise a standard in effect at the time of enactment of 
the 1990 Clean Air Act Amendments. Section 172(a)(1)(A) provides EPA 
with authority to classify nonattainment areas on or after the 
designation of an area as nonattainment with respect to ``any revised 
standard, including a revision of any standard in effect on the date of 
the enactment of the Clean Air Act Amendments of 1990.'' Plainly, 
Congress had no intention of prohibiting EPA from revising any of the 
ambient standards in effect at the time of the enactment of the 1990 
amendments.
    Third, the provisions of subpart 2 of Part D do not support the 
contention that they somehow preclude EPA from exercising its authority 
to revise the NAAQS under section 109. The fact that Congress laid out 
an implementation program for the O3 standard existing at 
the time of the 1990 amendments in no way suggests that Congress 
intended to preclude EPA from exercising the authority it provided EPA 
to revise the NAAQS when the health data on which EPA bases such 
decisions warranted a change in the standard. Contrary to this 
contention, section 181(a) does not preclude the designation of areas 
as nonattainment for O3 that have design values less than 
0.121 ppm. EPA has designated as nonattainment numerous areas whose 
design value was less than 0.121 ppm, but which violated the existing 
1-hour, 0.12 ppm O3 standard. These areas, referred to as 
``nonclassifiable nonattainment areas,'' include ``submarginal'' areas 
(i.e., O3 nonattainment areas with design values below 0.121 
ppm), (See 57 FR 13498, 13524-27, April 16, 1992). These areas include 
areas that were designated nonattainment prior to the 1990 amendments 
and whose nonattainment designation Congress required to be continued 
after 1990. See section 107(d)(1)(C)(i). Clearly, Congress did not 
prohibit the designation of areas as nonattainment for O3 
with design values below 0.121 ppm; in fact, in some cases, Congress 
required it. Furthermore, the position advanced by the commenters would 
mean that, in effect, Congress in the 1990 amendments legislatively 
revised the then-existing 1-hour, 0.12 ppm O3 standard to a 
0.121 ppm standard. There is no indication that Congress intended to do 
that.
    In addition, the fact that Congress directed EPA to use ``the 
interpretation methodology issued by the Administrator most recently'' 
before the date of the enactment of the Clean Air Act Amendments of 
1990 in the context of subpart 2 does not add any support to the 
commenters' position; it merely shows that Congress intended the 
existing 1-hour, 0.12 ppm standard to be implemented in a specified 
way, not that Congress intended to preclude EPA from using its 
otherwise applicable authority to revise the standard.
    The EPA also disagrees with the contention that sections 
172(a)(1)(C) and (a)(2)(D), which provide that the general 
classification and attainment date provisions of section 172 do not 
apply to areas for which classifications or attainment dates ``are 
specifically provided under other provisions of this part,'' support 
the conclusion that Congress intended to prohibit EPA from revising the 
O3 standard. These provisions simply mean that where 
Congress elsewhere provided for specific classifications and attainment 
dates, as in the case of subpart 2 regarding the 1-hour, 0.12 ppm 
standard, EPA is not to modify those

[[Page 38885]]

classifications or dates. The EPA is not purporting to do this. These 
provisions do not lead to the conclusion that because Congress 
established them for the O3 standard in effect at the time 
of the 1990 amendments, Congress meant that EPA could not revise that 
standard in order to appropriately protect public health.
    EPA does not accept the thesis that revising the O3 
standard forces EPA to violate other provisions of the Act and, 
therefore, is not an ``appropriate'' revision of the standard under 
section 109. Revising the O3 standard in accordance with the 
language of section 109 does not result in EPA violating any provision 
of the Act. On the other hand, a determination by EPA that the 
O3 standard should not be revised, even though EPA concludes 
that it needs to be revised to protect public health with an adequate 
margin of safety, would violate section 109.
    Also, EPA does not believe that carrying out the provisions of 
section 109 to set a new O3 standard to protect public 
health with an adequate margin of safety somehow ``risks undermining 
both perceptions and reality of the functioning of our democratic form 
of government.'' EPA is merely implementing the words of the Clean Air 
Act, a statute passed by the Congress and signed by the President. To 
refuse to revise the standard notwithstanding the need to protect 
public health as enunciated in section 109 would thwart the objectives 
of those who passed and signed the Clean Air Act on behalf of the 
American public.
    Finally, for the reasons stated above, EPA's analysis of its 
ability to implement the revised O3 standard under the 
provisions of subpart 1 of Part D of Title I does not support the view 
that Congress prohibited EPA from revising the standard. Congress 
clearly specified an approach to the implementation of the 1-hour, 0.12 
ppm O3 standard in the provisions of subpart 2 of Part D. 
EPA believes that the clear and express linkage of that approach to the 
1-hour, 0.12 ppm standard indicates that it may implement a revised 
O3 standard in accord with the general principles of subpart 
1 of Part D, as informed by the no-backsliding principle embodied in 
section 172(e). That Congress directed specifically how EPA and the 
States should implement the 1-hour, 0.12 ppm O3 standard 
does not carry with it the implication that Congress intended to 
prohibit EPA from exercising its otherwise clear and express authority 
to revise that standard in order to carry out one of its fundamental 
missions, the establishment of ambient air quality standards to protect 
public health with an ample margin of safety. If Congress had intended 
to prohibit EPA from exercising such a fundamental authority it would 
have clearly specified (as it did in other instances) that EPA could 
not do so.
    The EPA also disagrees with the contention that a revised 
O3 standard may not be implemented for so long as the 
current 1-hour, 0.12 ppm O3 standard remains in effect. The 
fact that the provisions of subpart 2 of Part D are focused on the 
implementation of the current standard does not mean that, if a new or 
revised O3 standard is promulgated pursuant to section 109, 
the new standard could not simultaneously be implemented under the 
provisions of section 110 and subpart 1 of Part D, which apply 
regardless of the criteria pollutant of concern. There is no language 
in sections 181 or 182 that precludes the implementation of a different 
standard under other authority; those provisions simply govern the 
implementation of the 1-hour, 0.12 ppm O3 standard. EPA 
further notes that it has historically had more than one primary 
standard for criteria pollutants (e.g., annual and 24-hour 
PM10 and sulfur dioxide standards, and 8-hour and 1-hour CO 
standards) and believes that had Congress wanted to preclude EPA from 
implementing two primary O3 standards simultaneously it 
would have expressly precluded EPA from doing so. Thus, EPA does not 
believe that it must repeal the 1-hour, 0.12 ppm O3 standard 
before it can promulgate and implement a new primary O3 
standard.

V. Technical Changes to Part 50

    In the proposal, the EPA proposed two alternative secondary 
standards: (1) A secondary standard set identical to the proposed 0.08 
ppm, 8-hour primary standard; or (2) a seasonal secondary standard 
expressed in the SUM06 form. For the reasons discussed in Unit III, the 
EPA has decided to promulgate a secondary ambient air quality standard 
for O3 that is identical to the primary ambient air quality 
standard. Accordingly, the language adopted in the final regulation (40 
CFR 50.10) has been revised to reflect this change.
    In the proposal, the regulatory text in Sec. 50.9 inadvertently 
included language about what it means when the standard is not met, 
that should have been discussed in 40 CFR part 50, Appendix H. 
Therefore this sentence has been removed from Sec. 50.10(b), and the 
discussion moved to the new Appendix I to 40 CFR part 50, which now 
provides additional clarification on calculations for sites with less 
than complete data, as discussed in Unit VI. of this preamble.

VI. Revisions to Appendices D, E, and H

    The EPA is finalizing the changes to Appendices D and E to 40 CFR 
part 50, that were proposed and described in the proposal. No adverse 
comments were received on these changes.
    Because the revocation of the existing 1-hour standard will become 
effective at a later date (as discussed above in Unit II.B.4.), EPA is 
retaining Appendix H in its current form. A new Appendix I explains the 
computations necessary for determining when the new 8-hour primary and 
secondary standards are met.
    The new Appendix I addresses data completeness requirements, data 
reporting, handling, and rounding conventions, and example 
calculations. The discussion in this unit sometimes refers to the 
contents of the new Appendix I as revisions to Appendix H, so as to 
highlight how the new Appendix I differs from the current Appendix H. 
For example, the example calculations in Appendix I differ from those 
in Appendix H to reflect the final form of the new 8-hour primary 
standard.
    In the proposal, two alternative secondary standards were proposed, 
and the proposed changes to Appendix H addressed both alternatives: A 
secondary standard set identical to the proposed 0.08 ppm, 8-hour 
primary standard; or a seasonal secondary standard expressed in the 
SUM06 form. For the reasons discussed above, the Administrator has 
decided to set the secondary standard identical to the primary standard 
as reflected in Appendix I.
    Key elements of Appendix I, particularly as they differ from those 
of Appendix H, are outlined below.

A. Data Completeness

    One key change to Appendix H, incorporated into Appendix I, for the 
new 0.08 ppm, 8-hour primary and secondary standards is that no 
numerical adjustment is made to the measured 8-hour concentrations to 
account for missing or incomplete data as was the case with the 1-hour 
standard. Instead, the EPA has decided to replace the methodology used 
to adjust the computation of estimated exceedances for missing data 
under the 1-hour standard with new data completeness requirements for 
the 8-hour standards.
    The EPA proposed that, in order to determine that the 8-hour 
standards have been met at a monitoring site

[[Page 38886]]

during the current 3-year period, revisions to Appendix H would require 
90 percent data completeness, on average, with no single year at the 
site having less than 75 percent data completeness. A site could be 
found not to have met the standards with less than complete data. 
Almost all commenters supported deleting the estimated exceedances 
missing data adjustment procedure of the current 1-hour standard and 
replacing it with minimum data completeness requirements. Several 
commenters felt that the proposed data completeness requirement might 
be too stringent and would be difficult to attain. Other commenters 
recommended that some consideration be made for hours lost due to 
instrument calibration. A few commenters thought that EPA should 
establish higher minimum data completeness requirements.
    Based on its analysis of available air quality data, the EPA 
believes that, with the changes to the proposal described below, the 
data completeness requirement in Appendix I is reasonable given that 90 
percent of all monitoring sites that currently operate on a continuous 
basis meet this objective. The EPA believes that a missing hour during 
the day resulting from instrument calibration should not negatively 
impact the ability of a monitoring site to meet the data completeness 
requirements because data completeness is based on the number of days 
with valid daily maximum 8-hour concentrations, not on the number of 
non-missing hours.
    In the proposal, the EPA sought comment on whether meteorological 
data could provide an objective basis for determining, on a day for 
which there is missing data, that the meteorological conditions were 
not conducive to high O3 concentrations, and therefore, that 
the day could be assumed to have an 8-hour daily maximum O3 
concentration less than 0.08 ppm. Under the 0.12 ppm 1-hour standard, a 
missing day is assumed less than the level of the standard only if the 
two adjacent days are non-missing, and the daily maximum 1-hour 
concentration on each of those days is less than or equal to 0.09 ppm. 
In the proposal, the EPA specifically requested comment on the 
appropriateness of using data on meteorological conditions, as well as 
on other information that would permit better definition of those 
necessary conditions likely to result in peak 8-hour O3 
concentrations in the ranges of concern. Most commenters expressing an 
opinion supported the use of meteorological data, as well as ambient 
data from nearby monitoring sites to establish that missing hours could 
be assumed less than the level of the standard. Days assumed less than 
the level of the standard would be counted as non-missing when 
computing whether the data completeness requirements have been met at 
the site. Taking these comments into account, EPA has revised the 
proposed revisions to Appendix H, as reflected in Appendix I, to count 
missing days assumed less than the standard when computing whether the 
data completeness requirement has been met. EPA will develop guidance 
on methodologies necessary for using meteorological data and ambient 
measurements to make such determinations.
    Several commenters expressed concerns about the possibility that 
stratospheric O3 intrusion from aloft or forest fires may 
lead to exceedances of the level of the standard, particularly within 
the context of peak O3 concentrations that have been 
observed at background sites. Commenters expressed concern that such 
events could lead to violations of the 8-hour standard and, therefore, 
they questioned the attainability of the proposed standard. Consistent 
with a forthcoming update to EPA's policy on natural events for the new 
8-hour standard, EPA has revised Appendix H to specifically address 
this concern by stating that whether to use data affected by 
stratospheric O3 intrusion or other natural events when 
determining if the standards have been met is subject to the approval 
of the appropriate Regional Administrator.

B. Data Handling and Rounding Conventions

    For the reasons cited above, and taking into account the advice of 
CASAC, the Administrator has set the level of the new 8-hour primary 
and secondary standards at 0.08 ppm. As EPA explained in the proposal, 
the level of the 8-hour standard is expressed to the second decimal 
place, 0.08 ppm, with the support of CASAC and in part to reflect 
uncertainties in the health effects evidence upon which the proposed 
standard is based. More specifically, these uncertainties include the 
measurement uncertainty and representativeness inherent in the reported 
ambient O3 concentrations used in field and epidemiological 
studies and the uncertainty in the exposure estimates upon which 
quantitative risk assessments have been based. In the proposal, EPA 
stated its belief that expressing the proposed standard to the second 
decimal place is also consistent with the quality assurance guidelines 
that indicate the precision61 for such O3 
measurements shall be within  15 percent.
---------------------------------------------------------------------------

    61 The term precision is used to denote both the reproducibility 
of a measurement under a constant set of conditions, as well as 
other components of measurement uncertainty such as instrument drift 
and relative bias.
---------------------------------------------------------------------------

    To determine whether the standard is met, EPA proposed that the 
calculated value of the third-highest maximum 8-hour average 
concentrations, averaged over 3 years, is compared to the level of the 
standard. It is the level of the standard, 0.08 ppm, expressed to two 
decimal places that determines the number of significant digits to be 
used when comparing air quality measurements to the standard. The EPA 
proposed that, for hourly data, 8-hour average O3 
concentrations computed from such hourly data, and the 3-year averages 
of the third highest maximum 8-hour average concentrations, that the 
third decimal place is carried forward as the rounding digit, and the 
insignificant digits are truncated. To compare the calculated 3-year 
average O3 concentration to the level of the standard, the 
third decimal place of the calculated value is rounded. The current 
rounding convention is to round up digits equal to or greater than 5.
    In the proposal, EPA recognized that the level of public health 
protection afforded by the use of the current rounding convention could 
be increased by replacing the current rounding convention with a 
convention that defined the smallest increment above the level of the 
standard to be 0.001 ppm for the purposes of determining whether the 
standard has been met. The EPA solicited comment on the use of such an 
alternative rounding convention, with regard to potential increased 
public health protection, as well as to potential effects on the 
probability of attainment misclassifications and on the stability of 
the standard.
    Of the many States that commented specifically on the rounding 
convention, most State agencies cited concerns by their monitoring 
staffs about the precision and accuracy of measured O3 
concentrations in ambient environments and recommended maintaining the 
current rounding convention. A tribal association also supported the 
current rounding convention. Other State agencies felt that newer 
instruments were capable of supporting a rounding convention set at 
0.001 ppm. Of those environmental and health associations that 
commented, all supported replacing the current rounding convention with

[[Page 38887]]

the alternative 0.001 ppm convention.62 All industry and 
trade associations that commented on rounding recommended that EPA 
retain the current rounding convention.
---------------------------------------------------------------------------

    62 One individual commenter provided an analysis of current 
monitoring technology and suggested that the precision and accuracy 
data supported setting the standard to three decimal places and 
rounding the annual average third-highest 8-hour average 
concentration up at 0.001 ppm. EPA believes that the precision and 
accuracy data cited by the commenter does not capture all of the 
uncertainty inherent in ambient air quality measurements.
---------------------------------------------------------------------------

     After taking these comments into account, EPA has decided that the 
current rounding approach is appropriate for comparing monitoring data 
to the level of the standard expressed to two decimal places. The 
current rounding procedure has the effect of reducing the probability 
of misclassifying an attainment area as nonattainment and of producing 
a more stable attainment test. The EPA believes that measures that 
promote a stable control program will lead to greater long-term health 
protection and risk reduction. For the reasons stated above, and taking 
into account the uncertainty in the exposure estimates upon which 
quantitative risk assessments have been based, measurement uncertainty, 
data representativeness, and the desirability of these resulting 
effects, EPA is retaining the current rounding convention and 
finalizing the data handling and rounding conventions, in Appendix I, 
as proposed.

VII. Regulatory and Environmental Impact Analyses

    As discussed in Unit IV of this preamble, the Clean Air Act and 
judicial decisions make clear that the economic and technological 
feasibility of attaining ambient standards are not to be considered in 
setting NAAQS, although such factors may be considered in the 
development of State plans to implement the standards. Accordingly, 
although, as described below, a Regulatory Impact Analysis (RIA) has 
been prepared, neither the RIA nor the associated contractor reports 
have been considered in issuing this final rule.

A. Executive Order 12866

    Under Executive Order 12866, 58 FR 51735 (October 4, 1993), the 
Agency must determine whether a regulatory action is ``significant'' 
and, therefore, subject to Office of Management and Budget (OMB) review 
and other requirements of the Executive Order. The order defines 
``significant regulatory action'' as any regulatory action that is 
likely to result in a rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or tribal governments or 
communities.
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another Agency.
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations of recipients 
thereof.
    (4) Raise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    In view of its important policy implications, this action has been 
judged to be a ``significant regulatory action'' within the meaning of 
the Executive Order. As a result, under section 6 of the Executive 
Order, EPA has prepared an RIA, entitled ``Regulatory Impact Analysis 
for Particulate Matter and Ozone National Ambient Air Quality Standards 
and Proposed Regional Haze Rule (July 1997).'' This RIA assesses the 
costs, economic impacts, and benefits associated with potential State 
implementation strategies for attaining the PM and O3 NAAQS 
and the proposed Regional Haze Rule. Changes made in response to OMB 
suggestions or recommendations will be documented in the public docket 
and made available for public inspection at EPA's Air and Radiation 
Docket Information Center (Docket No. A-95-58). The RIA will be 
publicly available in hard copy by contacting the U.S. Environmental 
Protection Agency Library at the address under ``Availability of 
Related Information'' and in electronic form as discussed above in 
``Electronic Availability.''

B. Regulatory Flexibility Analysis

    The Regulatory Flexibility Act (RFA), 5 U.S.C. 601 et seq., 
provides that, whenever an agency is required to publish a general 
notice of rulemaking for a proposed rule, the agency must prepare an 
initial regulatory flexibility analysis for the proposed rule unless 
the head of the agency certifies that the rule ``will not, if 
promulgated, have a significant economic impact on a substantial number 
of small entities'' (section 605(b)). The EPA certified each of the 
proposed NAAQS rules based on its conclusion that the rule would not 
establish requirements applicable to small entities and therefore would 
not have a significant economic impact on small entities within the 
meaning of the RFA. See 61 FR 65638, 65668 (PM proposal); 61 FR 65716, 
65746 (ozone proposal), both published on December 13, 1996. 
Accordingly, the Agency did not prepare an initial regulatory 
flexibility analysis for the proposed rule, but it did conduct a more 
general analysis of the potential impact on small entities of possible 
State strategies for implementing any new or revised NAAQS.
    At the heart of EPA's certification of the proposed NAAQS rule was 
the Agency's interpretation of the word ``impact'' as used in the RFA. 
Is the ``impact'' to be analyzed under the RFA a rule's impact on the 
small entities that will be subject to the rule's requirements, or the 
rule's impact on small entities in general, whether or not they will be 
subject to the rule? In the case of NAAQS rules, the question arises 
because of the congressionally-designed mixture of Federal and State 
responsibilities in setting and implementing the NAAQS.
    As EPA explained in the proposal, NAAQS rules establish air quality 
standards that States are primarily responsible for meeting. Under 
section 110 and part D of Title I of the CAA, every State develops a 
State Implementation Plan (SIP) containing the control measures that 
will achieve a newly promulgated NAAQS. States have broad discretion in 
the choice of control measures. As the U.S. Supreme Court noted in 
Train v. NRDC:

    [P]rimary [NAAQS] deal with the quality of outdoor air and are 
fixed on a nationwide basis at a level which the agency determines 
will protect the public health. It is the attainment and maintenance 
of these standards which section 110(a)(2)(A) requires that State 
plans provide. In complying with this requirement, a State's plan 
must include ``emission limitations'' which are regulations of the 
composition of substances emitted into the ambient air from such 
sources as power plants, service stations and the like. They are the 
specific rules to which operators of pollution sources are subject 
and which, if enforced, should result in ambient air which meets the 
national standards.
    The Agency is plainly charged by the Act with the responsibility 
for setting the national ambient air standards. Just as plainly, it 
is relegated to a secondary role in the process of determining and 
enforcing the specific, source-by-source emission limitations which 
are necessary if the national standards are to be met. Under 
110(a)(2), the Agency is required to approve a State plan which 
provides for the timely attainment and maintenance of the ambient 
air standards, and which also satisfies that section's other general 
requirements. The Act gives the agency no authority to question the 
wisdom of a State's choices of emission limitations if they are part 
of a plan which satisfies the standards of 110(a)(2) and the Agency 
may devise and promulgate a plan of

[[Page 38888]]

its own only if the state fails to submit an implementation plan 
which satisfies those standards. Section 110(c).

421 U.S. 60, at 78-79 (1975) (emphasis in original). In short, NAAQS 
rules themselves do not establish any control requirements applicable 
to small entities. State rules implementing the NAAQS may establish 
such requirements and the extent to which they do depends primarily on 
each State's strategy for meeting the NAAQS.63
---------------------------------------------------------------------------

    63 It is worth noting that Federal rules that apply nationally 
also play a role in reducing emissions governed by NAAQS. For 
instance, EPA rules under Title II of the CAA require reductions in 
ozone-forming emissions from on and off-road vehicles and the fuels 
that power them. When EPA issues such rules, it conducts the 
analysis required under the RFA. For example, EPA performed 
regulatory flexibility analyses for the reformulated gasoline rule 
issued under section 211(k) of the CAA. See 59 FR 7716, February 16, 
1994.
---------------------------------------------------------------------------

    To determine the proper interpretation of ``impact'' under the RFA, 
EPA considered the RFA's stated purpose, its requirements for 
regulatory flexibility analyses, its legislative history, the 
amendments made by the Small Business Regulatory Enforcement Fairness 
Act of 1996 (SBREFA)(Pub. L. 104-121), and caselaw. The EPA concluded 
that all of these traditional tools of statutory construction point in 
one direction--that an agency is required to assess the impact of a 
rule on the small entities that will be subject to the rule's 
requirements, because the purpose of a regulatory flexibility analysis 
is to consider ways of easing or even waiving a rule's requirements as 
they will apply to small entities, consistent with the statute 
authorizing the rule. That purpose cannot be served in the case of the 
rules like the NAAQS that do not have requirements that apply to small 
entities.
    More specifically, EPA noted that its interpretation of ``impact'' 
flows from the express purpose of the RFA itself. As the RFA's 
``Findings and Purposes'' section (Pub. L. 96-354, section 2) makes 
clear, Congress enacted the RFA in 1980 out of concern that agencies 
were writing one-size-fits-all regulations that in fact did not fit the 
size and resources of small entities. Congress noted that it is 
generally easier for big businesses to comply with regulations, and 
that small businesses are therefore at a competitive disadvantage in 
complying with uniform rules. Congress also noted that small entities' 
relative contribution to the problem a rule is supposed to solve may 
not warrant applying the same requirements to large and small entities 
alike. In the RFA itself, Congress therefore stated:

    It is the purpose of this Act to establish as a principle of 
regulatory issuance that agencies shall endeavor, consistent with 
the objectives of the rule and of applicable statutes, to fit 
regulatory and informational requirements to the scale of the 
businesses, organizations, and governmental jurisdictions subject to 
regulation.

[Pub. L. 96-354, section 2(b).]

    The EPA further noted that the RFA sections governing initial and 
final regulatory flexibility analyses reflect this statement of 
purpose. RFA sections 603 and 604 require that initial and final 
regulatory flexibility analyses identify the types and estimate the 
numbers of small entities ``to which the proposed rule will apply'' 
(sections 603(b)(3) and 604(a)(3)). Similarly, they require a 
description of the ``projected reporting, recordkeeping and other 
compliance requirements of the proposed rule, including an estimate of 
the classes of small entities which will be subject to the 
requirement'' (sections 603(b)(4) and 604(a)(4)). At the core of the 
analyses is the requirement that agencies identify and consider 
``significant regulatory alternatives'' that would ``accomplish the 
stated objectives of applicable statutes and which minimize any 
significant economic impact of the proposed rule on small entities'' 
(section 603(c) and 604(a)(5)). Among the types of alternatives 
agencies are to consider are the establishment of different 
``compliance or reporting requirements or timetables'' for small 
entities and the exemption of small entities ``from coverage of the 
rule, or any part'' of the rule (section 603(c)(1) and (4)). The RFA 
thus makes clear that regulatory flexibility analyses are to focus on 
how to minimize rule requirements on small entities.
    As EPA further explained, since regulatory flexibility analyses are 
not required for a rule that will not have a ``significant economic 
impact on a substantial number of small entities,'' it makes sense to 
interpret ``impact'' in light of the requirements for such analyses. 
Regulatory flexibility analyses, as described above, are to consider 
how a rule will apply to small entities and how its requirements may be 
minimized with respect to small entities. In this context, ``impact'' 
is appropriately interpreted to mean the impact of a rule on the small 
entities subject to the rule's requirements.
    The Agency cited two Federal court cases in support of its 
interpretation. In Mid-Tex Elec. Co-op v. FERC, 773 F.2d 327, 342 (D.C. 
Cir. 1985), petitioners claimed that the RFA required an agency to 
analyze the effects of a rule on small entities that were not regulated 
by the rule but might be indirectly impacted by it. Petitioners noted 
that the Small Business Administration (SBA) also interpreted the RFA 
to require analysis of a rule's impact on small entities not regulated 
by the rule, and argued that the court should defer to the SBA's 
position in light of its compliance monitoring role under the RFA. 
After reviewing the RFA's ``Findings and Purposes'' section, its 
legislative history, and its requirements for regulatory flexibility 
analyses, the Mid-Tex court rejected petitioners' interpretation. As 
the court explained:

    The problem Congress stated it discerned was the high cost to 
small entities of compliance with uniform regulations, and the 
remedy Congress fashioned--careful consideration of those costs in 
regulatory flexibility analyses--is accordingly limited to small 
entities subject to the proposed regulation. *** [W]e conclude that 
an agency may properly certify that no regulatory flexibility 
analysis is necessary when it determines that the rule will not have 
a significant economic impact on a substantial number of small 
entities that are subject to the requirements of the rule.

Id. at 342. Notably, Congress let this interpretation stand when it 
recently amended the RFA in enacting the SBREFA.
    The EPA also cited a recent case affirming the Mid-Tex court's 
interpretation. In United Distribution Companies v. FERC, 88 F.3d 1105, 
1170 (D.C. Cir. 1996), the court noted that the Mid-Tex court:

    *** conducted an extensive analysis of the RFA provisions 
governing when a regulatory flexibility analysis is required and 
concluded that no analysis is necessary when an agency determines 
``that the rule will not have a significant economic impact on a 
substantial number of small entities that are subject to the 
requirements of the rule''.

Id., citing and quoting Mid-Tex (emphasis added by United Distribution 
court).
    The Agency went on to explain that given the Federal/State 
partnership for attaining healthy air, the proposed NAAQS, if adopted, 
would not establish any requirements applicable to small entities. 
Instead, any new or revised standard would establish levels of air 
quality that States would be primarily responsible for achieving by 
adopting plans containing specific control measures for that purpose. 
The proposed NAAQS rule was thus not susceptible to regulatory 
flexibility analysis as prescribed by the amended RFA. Since it would 
establish no requirements applicable to small entities, it afforded no 
opportunity for EPA to fashion for small entities less burdensome 
compliance or reporting requirements or timetables, or

[[Page 38889]]

exemptions from all or part of the rule. For these reasons, EPA 
certified that the proposed rule ``will not, if promulgated, have a 
significant economic impact on a substantial number of small 
entities,'' within the meaning of the RFA. Because EPA was not required 
to prepare an initial regulatory flexibility analysis for the rule, it 
was also not required to convene a Small Business Advocacy Review Panel 
for the rule under RFA section 609(b) as added by SBREFA.
    Notwithstanding its certification of the proposed rule, EPA 
recognized that the proposed NAAQS, if adopted, would begin a process 
of State implementation that could eventually lead to small entities 
having to comply with new or different control measures, depending on 
the implementation plans developed by the States. EPA also recognized 
that the CAA does not allow EPA to dictate or second-guess how States 
should exercise their discretion in regulating to attain any new or 
revised NAAQS. Under those circumstances, EPA concluded that the best 
way to take account of small entity concerns regarding any new or 
revised NAAQS was to work with small entity representatives and States 
to provide information and guidance on how States could address small 
entity concerns when they write their implementation plans.
    In line with this approach, as part of the RIA it prepared for the 
proposed NAAQS, EPA analyzed how hypothetical State plans for 
implementing the proposed rule might affect small entities. The 
analysis was necessarily speculative and limited, since it depended on 
projections about what States might do several years in the future and 
did not take into account any new strategies that might be developed 
and recommended by the FACA subcommittee formed to help devise 
potential strategies for implementing a new or revised NAAQS (see 
discussion of RIA and FACA process in the previous Unit of this 
notice). Nevertheless, the analysis provided as much information on 
potential small entity impacts as was reasonably available at the time 
of the proposed rule.
    The Agency also took steps to ensure that small entities' voices 
were heard in the NAAQS rulemaking itself. With Jere Glover, Chief 
Counsel for Advocacy of the SBA, EPA convened outreach meetings modeled 
on the SBREFA panel process to solicit and convey small entities' 
concerns with the proposed NAAQS. Two meetings were held as part of 
that process, on January 7 and February 28, 1997, with a total 
attendance of 41 representatives of small businesses, small governments 
and small nonprofit organizations. Both meetings were attended by 
representatives of SBA and the Office of Management and Budget, as well 
as of EPA. The key concerns raised by small entities at those meetings 
related to the scientific foundation of the proposed NAAQS and the 
potential cost of implementing it, the same concerns raised by other 
industry commenters on the proposed rule. The Agency produced a report 
on the meetings to ensure that small entity concerns were part of the 
rulemaking record when EPA made its final decision on the proposal.
    In light of States' pivotal role in NAAQS implementation, EPA also 
undertook a number of additional activities to assist and encourage the 
States to be sensitive to small entity impacts as they implement any 
new or revised NAAQS. With the SBA, EPA began an interagency panel 
process to collect advice and recommendations from small entity 
representatives on how States could lessen any impacts on small 
entities. The EPA plans to issue materials in two phases to help States 
develop their implementation plans. In view of States' discretion in 
implementing the NAAQS, these materials will mostly take the form of 
guidance, which is not subject to the RFA's requirement for initial 
regulatory flexibility analysis. (Under RFA section 603, that 
requirement applies only to binding rules that are required to undergo 
notice-and-comment rulemaking procedures.) But regardless of the form 
such materials take, EPA is employing panel procedures to ensure that 
small entities have an opportunity to raise any concerns prior to the 
materials being issued in draft form.
    To supplement the input the Agency receives from the ongoing CAAAC 
process (described earlier in this Unit of this preamble), EPA also 
added more small entity representatives to the subcommittee on 
implementation of any new or revised NAAQS. These representatives have 
formed a small entity caucus to develop and bring to the subcommittee a 
focused approach to small entity issues. These new subcommittee members 
are also part of the group in the aforementioned panel process. By 
means of these various processes, EPA hopes to promote the 
consideration of small entity concerns and advice throughout the NAAQS 
implementation process.
    In response to the proposed rule, a number of commenters questioned 
EPA's decision to certify that the proposed NAAQS will not have a 
significant impact on a substantial number of small entities. Some 
commenters disagreed with EPA's view that the proposed NAAQS would not 
establish regulatory requirements applicable to small entities. These 
commenters argued that a number of control requirements applicable to 
small entities would automatically result from promulgation of the 
proposed NAAQS, such as new reasonable further progress, SIP and 
Federal Implementation Plan (FIP) requirements. Other commenters stated 
that it is possible for EPA to assess the impacts of the NAAQS revision 
on small entities and that, to a limited extent, EPA has already done 
so. Further, a number of commenters argued that EPA has a legal 
obligation under the RFA, as amended by SBREFA, to choose a NAAQS 
alternative that minimizes the impact on small entities. Some 
commenters questioned EPA's interpretations of the Mid-Tex and United 
Distribution cases. In addition, other commenters stated that EPA's 
position regarding the NAAQS and the RFA is inconsistent with its past 
practice and the legislative history of the RFA. Finally, a few 
commenters noted that the panel process EPA conducted for the proposed 
NAAQS did not satisfy the requirements of SBREFA.
    EPA disagrees that promulgation of the NAAQS will automatically 
result in control requirements applicable to small entities that EPA 
can and must analyze under the RFA. As noted previously, a NAAQS rule 
only establishes a standard of air quality that other CAA provisions 
call on States (or in case of State inaction, the Federal government) 
to achieve by adopting implementation plans containing specific control 
measures for that purpose. Following promulgation of a new or revised 
NAAQS, section 110 of the CAA requires States and EPA to engage in a 
designation process to determine what areas within each State's borders 
are attaining or not attaining the NAAQS. Under section 110 and parts C 
and D of Title I of the CAA, States then conduct a planning process to 
develop and adopt their SIPs. Depending on an area's designation for 
the particular NAAQS, these and other Title I provisions require a 
State's SIP to contain certain control programs in addition to the 
control measures that the State decides are also needed to attain and 
maintain the NAAQS.
    The fact that the CAA requires SIPs to contain certain control 
programs under certain circumstances does not mean that EPA either can 
or must conduct a regulatory flexibility analysis of a rule 
establishing a NAAQS. Just from the standpoint of feasibility, EPA 
cannot know which areas will be subject to what mandatory SIP programs 
until

[[Page 38890]]

after the designation process is completed. Beyond that, any mandatory 
SIP programs are still implemented by the States, and States have 
considerable discretion in how they implement them. For instance, the 
reasonable further progress requirement under section 172 leaves States 
broad discretion to determine the rate of progress and the control 
measures to achieve that progress.64 As a result, EPA cannot 
be certain where and how any mandatory programs will be implemented 
with respect to small (or large) entities. Much less can EPA know about 
how States will exercise their discretion to develop additional 
controls needed to attain and maintain the NAAQS.
---------------------------------------------------------------------------

    64 Contrary to what some commenters assumed, the SIP 
requirements of subpart 2 of part D of Title I will not apply to 
SIPs to implement the revised ozone NAAQS. Those requirements were 
enacted by Congress in 1990 to address nonattainment of a 0.12 ppm 
1-hour ozone NAAQS. To the extent those requirements remain in 
effect, they apply only to SIPs for areas still in nonattainment 
with that standard; they do not apply to SIPs for areas in 
nonattainment only with respect to the ozone NAAQS adopted today. 
Further, to the extent SIPs for areas in nonattainment with the 
previous ozone standard remain subject to subpart 2 requirements, 
there will be no incremental change in the impact on sources 
regulated by the States' SIPs pursuant to the requirements as a 
result of today's promulgation.
---------------------------------------------------------------------------

    Even if EPA could know exactly how any mandatory SIP programs would 
apply to small entities, the purpose of the RFA is not served by 
attempting a regulatory flexibility analysis of State implementation of 
those programs. As explained previously, the RFA and the caselaw 
interpreting it clearly establish that the purpose of the RFA is to 
promote Federal agency efforts to tailor a rule's requirements to the 
scale of the small entities that will be subject to it. That purpose 
cannot be served in the case of a NAAQS rule since the rule does not 
establish requirements applicable to small entities. In promulgating a 
NAAQS, the only choice before EPA concerns the level of the standard, 
not its implementation. While mandatory SIP programs may ultimately 
follow from promulgation of the NAAQS, there is nothing EPA can do in 
setting the NAAQS to tailor those programs as they apply to small 
entities. Whether and how the programs will apply in particular 
nonattainment areas is beyond the scope of the NAAQS rulemaking and, 
indeed, beyond EPA's reach in any rulemaking to the extent the 
applicability and terms of the programs are prescribed by 
statute.65 Moreover, any mandatory SIP programs are 
supplemented by discretionary State controls that EPA has no power to 
tailor under the RFA or the CAA (see Train v. NRDC, quoted previously).
---------------------------------------------------------------------------

    65 If and when the Agency issues any rules addressing State 
implementation of any statutorily required actions, EPA would 
analyze and address the impact of those rules on small entities as 
appropriate under the RFA.
---------------------------------------------------------------------------

    The commenters' suggestions for minimizing the potential impact of 
the NAAQS rule on small entities run afoul of both the RFA and the CAA. 
Some suggested that EPA set a less stringent standard (or no standard 
at all in the case of PM2.5) to reduce the chance that small 
entities would become subject to new or tighter SIP requirements. 
Others suggested that EPA require States to exempt small entities from 
new or tighter SIP requirements. However, as explained in a previous 
Unit of this notice addressing the Agency's authority to consider 
factors other than public health in setting primary NAAQS, the RFA 
neither requires nor authorizes EPA to set a less stringent NAAQS than 
the applicable CAA provisions allow in order to reduce potential small 
entity impacts. Indeed, the RFA provides that any means of providing 
regulatory flexibility to small entities be consistent with the statute 
authorizing the rule. Moreover, even if EPA set a less stringent 
standard, States could still exercise their discretion to obtain any 
needed emission reductions from small entities. As the Supreme Court in 
Train v. NRDC made clear, EPA has no authority to forbid States from 
obtaining reductions from any particular category of stationary 
sources, including small entities. See also, Virginia v. EPA, No. 108 
F.3d 1397, 1408 (D.C. Cir. 1997), quoting Union Electric v. EPA, 427 
U.S. 246, 269 (1976) (``section 110 left to the states the power to 
determine which sources would be burdened by regulations and to what 
extent'').
    EPA's approval of SIPs for the new or revised NAAQS also will not 
establish new requirements, but will instead simply approve 
requirements that a State is already imposing. And again, EPA does not 
have authority to disapprove a State's plan except to the extent that 
the plan fails to demonstrate attainment and maintenance of the NAAQS 
as required by Title I of the CAA. In cases where EPA promulgates a 
FIP, EPA might establish control requirements applicable to small 
entities, and in such a circumstance, EPA would conduct the analyses 
required by the RFA.
    Some commenters argued that under the RFA as amended by SBREFA, EPA 
now has an obligation to choose the alternative that minimizes the 
impact on small entities when setting the NAAQS. As indicated above, 
EPA disagrees with the commenters' argument for the reasons stated in 
the Unit of this notice discussing the Agency's authority to consider 
costs and other factors not related to public health in setting and 
revising primary NAAQS. In a nutshell, both the text and legislative 
history of the RFA make clear that the RFA does not override the 
substantive provisions of the statute authorizing the rule, but only 
requires agencies to identify and consider ways of minimizing the 
economic impact on small entities subject to the rule in a manner 
consistent with the authorizing statute.
    Some commenters disagreed with EPA's interpretation of the Mid-Tex 
and United Distribution cases. In particular, these commenters noted 
that in those cases the relevant regulatory agency, FERC, wholly lacked 
jurisdiction to regulate the small entities at issue. According to 
these commenters, EPA does have the ability and jurisdiction to 
regulate small entities in the case of the NAAQS, and therefore EPA's 
reliance on Mid-Tex and United Distribution is misplaced.
    The commenters' attempt to distinguish the FERC cases from the 
NAAQS rulemaking wholly overlooks the courts' reasoning, which in fact 
fully supports EPA's certification of the proposed NAAQS. As described 
above, the Mid-Tex court exhaustively reviewed the relevant sections of 
the RFA and its legislative history. Its analysis revealed that 
Congress passed the RFA out of concern with one-size-fits-all 
regulations and fashioned a remedy limited to regulations that apply to 
small entities. This principle is fully applicable to the NAAQS, which 
creates no rule requirements that apply to small entities.
    The fact that FERC had no regulatory authority over the small 
entities indirectly affected by its rules played no essential role in 
the court's rationale. FERC could (and apparently did in the Mid-Tex 
rulemaking) estimate the potential indirect impact of its rules on 
small entities. Presumably, FERC could have also mitigated any indirect 
impact by changing some aspect of the rule (or else the small entities 
would have had no incentive to sue the agency). The court nevertheless 
found it unnecessary for FERC to do either, based on its reading of the 
RFA as limited to analysis of a rule's impact on the small entities 
subject to the rule's requirements. In reaching its decision, the court 
noted that requiring agencies to ``consider every indirect effect that 
any regulation might have on small businesses *** is a very broad and 
ambitious agenda, *** that Congress is unlikely to have embarked on *** 
without airing the matter.'' Mid-Tex, 773 F.d. at 343.
    The commenters also overstate EPA's regulatory authority over small 
entities

[[Page 38891]]

with respect to the regulation of criteria pollutants. Various CAA 
provisions authorize EPA to regulate various types of sources at the 
Federal level to accomplish specified goals. However, EPA's authority 
to more generally regulate sources, including small entities, in the 
manner of SIPs is limited to instances of State default of SIP 
responsibilities. When that occurs, EPA may issue a FIP containing 
specific control measures, and to the extent a proposed FIP would 
establish control measures applicable to small entities, EPA would 
analyze the small entity impact of those measures as required by the 
RFA. In 1994, for example, EPA prepared an initial regulatory 
flexibility analysis when it proposed a FIP for Los Angeles. See 59 FR 
23264, May 5, 1994.
    As noted above, Congress let the Mid-Tex interpretation stand when 
it recently amended the RFA in enacting SBREFA. If it had disagreed 
with the court's decision, it would have revised the relevant statutory 
provisions or otherwise indicated its disagreement when it enacted 
SBREFA. Instead, Congress actually reinforced the Mid-Tex court's 
interpretation of the RFA in enacting section 212(a) of SBREFA. That 
section requires that an agency issue a ``small entity compliance 
guide'' for ``each rule *** for which an agency is required to prepare 
a final regulatory flexibility analysis under section 604'' of the RFA. 
The guide is ``to assist small entities in complying with the rule'' by 
``explain[ing] the actions a small entity is required to take to 
comply'' with the rule (SBREFA section 212(a)). Obviously, it makes no 
sense to prepare a small entity compliance guide for a rule that does 
not apply to small entities. SBREFA thus stands as further confirmation 
that Congress intended regulatory flexibility analyses to address only 
rules that establish requirements small entities must meet. Since 
SBREFA's passage, the United Distribution court has affirmed the Mid-
Tex court's interpretation.
    Some commenters noted that EPA's informal panel process did not 
comply with the requirements of SBREFA. The EPA did not convene a 
SBREFA panel because such a panel is not required for rules like the 
NAAQS that do not apply to small entities. Under the RFA as amended by 
SBREFA, since the Agency certified the proposal, it was not required to 
convene a panel for it. Nevertheless, EPA conducted the voluntary panel 
process described above, as well as other voluntary small business 
outreach efforts. The process could not comply with the analytical 
requirements of the RFA for the reasons given above. However, it could 
and did ensure that EPA heard directly from small entities about the 
NAAQS proposals.
    A few commenters stated that EPA's view of the NAAQS and the RFA is 
inconsistent with EPA's past positions regarding the RFA and NAAQS 
revisions. Some commenters also cited the Regulatory Impact Analysis 
for the proposed NAAQS and noted that this analysis demonstrates EPA's 
ability to estimate the impact of the NAAQS on small entities, thereby 
undercutting EPA's argument that it is not able to perform a regulatory 
flexibility analysis when setting the NAAQS.
    Past Federal Register notices make clear that the nature of the 
NAAQS makes a regulatory flexibility analysis inapplicable to NAAQS 
rulemakings. For instance, in 1984, EPA stated that a ``NAAQS for NOx 
by itself has no direct impact on small entities. However, it forces 
each State to design and implement control strategies for areas not in 
attainment.'' 49 FR 6866, 6876, February 23, 1984; see also, 50 FR 
37484, 37499, September 13, 1985; 50 FR 25532, 25542, June 19, 1985 
(NAAQS for NO2 do not impact small entities directly). EPA 
stated again in 1987 that the NAAQS ``themselves do not contain 
emission limits or other pollution controls. Rather, such controls are 
contained in State implementation plans.'' 52 FR 24634, 24654, July 1, 
1987.
    EPA has typically performed an analysis to assess, to the extent 
practicable, the potential impact of retaining or revising the NAAQS on 
small entities, depending on possible State strategies for implementing 
the NAAQS. These analyses have provided as much insight into the 
potential small entity impacts of implementing revised NAAQS as could 
be provided at the NAAQS rulemaking stage. In some instances, these 
preliminary ``analyses'' were described as ``regulatory flexibility 
analys[es]'' or as analyses ``pursuant to this [Regulatory Flexibility] 
Act.'' See, e.g., 52 FR 24634, 24654, July 1, 1987; 50 FR 37484, 37499, 
September 13, 1985.
    However, these analyses were based on hypothetical State control 
strategies, and EPA made the point on various occasions that any 
conclusions to be drawn from such analyses were ``speculative,'' given 
that the NAAQS themselves do not impose requirements on small entities. 
Although these past analyses reflected the Agency's best efforts to 
evaluate potential impacts, they were not regulatory flexibility 
analyses containing the necessary elements required by the RFA. These 
analyses, for example, did not describe the ``reporting, recordkeeping 
and other compliance requirements'' of the proposed NAAQS rules that 
would apply to small entities, since the NAAQS rules did not apply to 
small entities. Nor did they determine how the proposed NAAQS rules 
could be eased or waived for small entities. Such an analysis is not 
possible in the case of the NAAQS. To the extent EPA labeled these 
analyses regulatory flexibility analyses in the past, that label was 
inappropriate. EPA's current practice is to describe such an analysis 
more accurately as a ``general analysis of the potential cost impacts 
on small entities.'' See, e.g., 61 FR 65638, 65669, 65747, December 13, 
1996 (current O3 and PM NAAQS proposals).66 EPA's 
analytical approach to small entity impacts of the NAAQS has thus 
remained consistent over time.
---------------------------------------------------------------------------

    66 As commenters pointed out, the RIA for the proposed PM NAAQS 
does state that ``[t]he screening analysis *** provides enough 
information for an initial regulatory flexibility analysis (RFA) if 
such an analysis were to be done.'' That statement was mistaken and 
was not made in the RIA for the proposed ozone NAAQS. While both 
RIAs attempted to gauge the potential impact on small entities of 
State implementation of the proposed NAAQS, neither could or did 
identify any specific control or information requirements contained 
in the NAAQS rule that would apply to small entities. Indeed, both 
RIAs made clear that the impact being analyzed was that of potential 
State measures to attain the NAAQS, and that such an analysis was 
inherently speculative and uncertain. Thus, the RIAs actually 
confirm EPA's statement in the preambles for the proposed NAAQS that 
conducting a complete regulatory flexibility analysis is not 
feasible for rules setting or revising a NAAQS.
---------------------------------------------------------------------------

    One commenter noted that the legislative history of the RFA 
suggests that the RFA was intended to apply to the NAAQS. As noted 
previously, EPA's reading of both the RFA and SBREFA, based on the 
language of the statute as amended and its legislative histories and 
applicable caselaw, is that the RFA requirements at issue do not apply 
to the NAAQS. The legislative history cited by the commenter does not 
change this conclusion.
    In fact, the statement by Senator Culver on which the commenter 
relies does not indicate that the NAAQS should be subject to regulatory 
flexibility analyses. Rather, Senator Culver uses the NAAQS as an 
example of the type of standard that agencies would not change as a 
result of the Regulatory Flexibility Act. According to Senator Culver, 
Section 606 ``succinctly states that this bill does not alter the 
substantive standard contained in underlying statutes which defines the 
agency's mandate.'' 126 Cong. Rec. S 21455 (Aug. 6, 1980) daily ed. 
After citing CAA section 109, Senator Culver goes on to describe EPA's 
bubble policy

[[Page 38892]]

(which addresses the limits on emissions from a particular facility) as 
the type of flexible regulation that agencies should consider, once EPA 
has set a NAAQS. ``The important point for purposes of this discussion 
is that the `bubble concept', a type of flexible regulation, in no 
manner altered the basic statutory substantive standard of the EPA *** 
. No regulatory flexibility analysis alters the substantive standard 
otherwise applicable by law to agency action.'' Id. Thus, contrary to 
the suggestion of the commenter, Senator Culver's statement actually 
confirms that the time to consider regulatory flexibility is when 
regulations applicable to sources are being established, not when a 
NAAQS itself is being set.
    Under section 604 of the RFA, whenever an agency promulgates a 
final rule under section 553 of the Administrative Procedure Act, after 
being required by that section or any other law to publish a general 
notice of proposed rulemaking (NPRM), the agency is required to prepare 
a final regulatory flexibility analysis. RFA section 605(b) provides, 
however, that section 603 (re initial regulatory flexibility analyses) 
and section 604 do not apply if the agency certifies that the rule will 
not have a significant economic impact on a substantial number of small 
entities and publishes such certification at the time of publication of 
the NPRM or at the time of the final rule.
    As noted above, EPA certified today's rule at the time of the NPRM. 
After considering the public comments on the certification, EPA 
continues to believe that today's rule will not have a significant 
economic impact on a substantial number of small entities for the 
reasons explained above and that it therefore appropriately certified 
the rule. Further, as required by the CAA, EPA is promulgating today's 
rule under CAA section 307(d). For all the foregoing reasons, EPA has 
not prepared a final regulatory flexibility analysis for the rule. The 
Agency has nonetheless analyzed in the final RIA for the rule the 
potential impact on small entities of hypothetical State plans for 
implementing the NAAQS. The Agency also plans to issue guidance to the 
States on reducing the potential impact on small entities of 
implementing the NAAQS.

C. Impact on Reporting Requirements

    There are no reporting requirements directly associated with the 
finalization of ambient air quality standards under section 109 of the 
Act (42 U.S.C. 7409). There are, however, reporting requirements 
associated with related sections of the Act, particularly sections 107, 
110, 160, and 317 (42 U.S.C. 7407, 7410, 7460, and 7617).

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Pub. 
L. 104-4, establishes requirements for Federal agencies to assess the 
effects of their regulatory actions on State, local, and tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures by State, local, and tribal governments, in 
the aggregate, or by the private sector, of $100 million or more in any 
one year. This requirement does not apply if EPA is prohibited by law 
from considering section 202 estimates and analyses in adopting the 
rule in question. Before promulgating an EPA rule for which a written 
statement is needed, section 205 of the UMRA generally requires EPA to 
identify and consider a reasonable number of regulatory alternatives 
and adopt the least costly, most cost-effective, or least burdensome 
alternative that achieves the objectives of the rule. These 
requirements do not apply when they are inconsistent with applicable 
law. Moreover, section 205 allows EPA to adopt an alternative other 
than the least costly, most cost-effective, or least burdensome 
alternative if the Administrator publishes with the final rule an 
explanation of why that alternative was not adopted. Before EPA 
establishes any regulatory requirements that may significantly or 
uniquely affect small governments, including tribal governments, it 
must have developed under section 203 of the UMRA a small government 
agency plan. The plan must provide for notifying potentially affected 
small governments, enabling officials of affected small governments to 
have meaningful and timely input in the development of EPA regulatory 
proposals with significant Federal intergovernmental mandates, and 
informing, educating, and advising small governments on compliance with 
the regulatory requirements. Section 204 of UMRA requires each agency 
to develop ``an effective process to permit elected officers of State, 
local and tribal governments *** to provide meaningful and timely 
input'' in the development of regulatory proposals containing a 
significant Federal intergovernmental mandate.67
---------------------------------------------------------------------------

    67 As noted in Unit VII.B. of this preamble, a NAAQS rule only 
establishes a standard of air quality that other provisions of the 
Act call on States (or in the case of State inaction, the Federal 
government) to achieve by adopting implementation plans containing 
specific control measures for the purpose. Thus, it is questionable 
whether the NAAQS itself imposes an enforceable duty and thus 
whether it is a significant Federal mandate within the meaning of 
UMRA. EPA need not and does not reach this issue today. For the 
reasons given in this unit, even if the NAAQS were determined to be 
a significant Federal mandate, EPA does not have any obligations 
under sections 202 and 205 of UMRA, and EPA has met any obligations 
it would have under section 204 of UMRA.
---------------------------------------------------------------------------

    The EPA has determined that the provisions of sections 202 and 205 
of the UMRA do not apply to this decision. ``Unless otherwise 
prohibited by law,'' EPA is to prepare a written statement under 
Section 202 of UMRA that is to contain assessments and estimates of the 
costs and benefits of a rule containing a Federal mandate. Congress 
clarified that ``unless otherwise prohibited by law'' referred to 
whether an agency was prohibited from considering the information in 
the rulemaking process, not to whether an agency was prohibited from 
collecting the information. The Conference Report on UMRA states, 
``This section [202] does not require the preparation of any estimate 
or analysis if the agency is prohibited by law from considering the 
estimate or analysis in adopting the rule.'' 141 Cong. Rec. H3063 
(daily ed. March 13, 1995). Because the Clean Air Act prohibits EPA, 
when setting the NAAQS, from considering the types of estimates and 
assessments described in section 202, UMRA does not require EPA to 
prepare a written statement under section 202.68 The 
requirements in section 205 do not apply because those requirements 
only apply to rules ``for which a written statement is required under 
section 202 ***.''
---------------------------------------------------------------------------

    68 In addition to the estimates and assessments described in 
section 202 of UMRA, written statements are also to include an 
identification of the Federal law under which the rule is 
promulgated (section 202(a)(1) of UMRA) and a description of 
outreach efforts under section 204 of UMRA (section 202(a)(5) of 
UMRA). Although these requirements do not apply here because a 
written statement is not required under section 202 of UMRA, this 
preamble identifies the Federal law under which this rule is being 
promulgated and a written statement describing EPA's outreach 
efforts with State, local, and tribal governments will be placed in 
the docket.
---------------------------------------------------------------------------

    The EPA has determined that the provisions of section 203 of UMRA 
do not apply to this decision. Section 203 only requires the 
development of a small government agency plan for requirements with 
which small governments might have to comply. Since setting the NAAQS 
does not establish requirements with which small governments might have 
to comply, section 203 does not apply. The

[[Page 38893]]

EPA acknowledges, however, that any corresponding revisions to 
associated State implementation plan requirements and air quality 
surveillance requirements, 40 CFR part 51 and 40 CFR part 58, 
respectively, might result in such effects. Accordingly, EPA will 
address unfunded mandates as appropriate when it proposes any revisions 
to 40 CFR parts 51 and 58.
    With regard to the outreach described in UMRA section 204, EPA did 
follow a process for providing elected officials with an opportunity 
for meaningful and timely input into the proposed NAAQS revisions, 
although EPA did not describe this process in the proposal. The EPA 
conducted a series of pre-proposal outreach meetings with State and 
local officials and their representatives that permitted these 
officials to provide meaningful and timely input on issues related to 
the NAAQS and the monitoring issues associated with them. Beginning in 
January, 1996, EPA briefed State and local air pollution control 
officials at national meetings with State and Territorial Air Pollution 
Program Administrators (STAPPA)/Association of Local Air Pollution 
Control Officials (ALAPCO) in Washington DC, North Carolina, Chicago 
and Nevada. The EPA also held briefings for the Washington DC 
representatives of several State and local organizations, including 
National Conference of State Legislators, U.S. Conference of Mayors, 
National Governors Association, and National League of Cities, and 
STAPPA/ALAPCO. EPA also held separate briefings and discussions with 
State and local officials at meetings set up by the National Governors 
Association, the U.S. Conference of Mayors and the Council of State 
Governments. The EPA also conducted in-depth briefings at each EPA 
regional office and regional staff also had several meetings and 
discussions with their State counterparts about the standards. The 
efforts described above, which provided elected officials with 
opportunity for meaningful and timely input into the proposed NAAQS 
revisions, met any requirements imposed by section 204. The docket will 
contain a written statement describing these outreach efforts, 
including a summary of the comments and concerns presented by State, 
local, and tribal governments and a summary of EPA's evaluation of 
those comments and concerns.
    Several commenters disagreed with EPA that UMRA sections 202, 203 
and 205 do not apply to this decision. These commenters argued that EPA 
is not prohibited from considering costs in setting NAAQS under the 
Clean Air Act and applicable judicial decisions. Some commenters also 
expressed the view that there is no conflict between UMRA and the Clean 
Air Act with regard to the NAAQS. These commenters argued that UMRA and 
the NAAQS can be ``harmonized'' by reading UMRA as an information 
gathering statute and that EPA should therefore perform the analyses 
required by UMRA, regardless of whether costs may be considered. 
Finally, at least one commenter argued that in past NAAQS reviews, EPA 
did not dispute its UMRA obligations.
    As discussed more fully in Unit IV of this preamble, EPA is 
prohibited from considering cost in setting the NAAQS. Given that fact 
(as noted in Unit IV preamble), sections 202 and 205 do not 
apply.69 As the Conference Report clarifies, UMRA itself 
states that the section 202 estimates and analyses are not required in 
cases such as the NAAQS, where an agency is prohibited by law from 
considering section 202 estimates and analyses. Reading UMRA in the 
manner suggested by the commenters would effectively read this 
provision out of UMRA; UMRA contains an exception for rules like the 
NAAQS, it must be given effect.
---------------------------------------------------------------------------

    69 One commenter argued that in reviewing the SO2 
NAAQS, EPA determined that it need not revise the SO2 
NAAQS, but could instead pursue an alternative regulatory program 
under other authority. This commenter argued that EPA has similar 
flexibility in reviewing the PM and Ozone NAAQS, and thus UMRA 
requires EPA to identify the least burdensome alternative (such as 
retaining the current NAAQS) as part of that process. As discussed 
more fully above at Unit IV of this preamble, EPA does not agree 
that it has flexibility to choose such an alternative; nor does EPA 
agree with the commenter's characterization of the action it took in 
deciding not to revise the SO2 NAAQS. In fact, in 
deciding not to revise the SO2 NAAQS, EPA determined, for 
reasons independent of section 303 of the Clean Air Act that a NAAQS 
revision was not warranted. See 61 FR 25566, 25575, May 22, 1996.
---------------------------------------------------------------------------

    With regard to EPA's position regarding UMRA in previous NAAQS 
review exercises, EPA simply made plain in those situations that 
because it did not plan on revising the NAAQS, it determined, without 
further review, that UMRA sections 202, 203 and 205 did not apply. EPA 
thus stated that:

    Because the Administrator has decided not to revise the existing 
primary NAAQS for SO2, this action will not impose any 
new expenditures on governments or on the private sector, or 
establish any new regulatory requirements affecting small 
governments. Accordingly, EPA has determined that the provisions of 
section 202, 203 and 205 do not apply to this final decision.

61 FR 25566, 25577, May 22, 1996; See also 61 FR 52852, 52856, October 
8, 1996 (Same statement for NO2 NAAQS). As this statement 
makes clear, EPA only determined that UMRA sections 202, 203 and 205 
did not apply to the NAAQS when EPA fails to revise the standard. 
Having made that determination, EPA had no reason to catalogue 
additional bases for finding UMRA inapplicable. Nothing in that 
statement was intended to preclude EPA, or precludes EPA, from 
concluding for other reasons (such as those discussed above) that UMRA 
also does not apply when EPA in fact revises an applicable NAAQS.

E. Environmental Justice

    Executive Order 12848 requires that each Federal agency make 
achieving environmental justice part of its mission by identifying and 
addressing, as appropriate, disproportionately high and adverse human 
health or environmental effects of its programs, policies, and 
activities on minorities and low-income populations. These requirements 
have been addressed to the extent practicable in the RIA cited above.

F. Submission to Congress and the Comptroller General

    Under 5 U.S.C. 801(a)(1)(A), as added by the Small Business 
Regulatory Enforcement Fairness Act of 1996 (SBREFA), EPA submitted a 
report containing this rule and other required information to the U.S. 
Senate, the U.S. House of Representatives, and the Comptroller General 
of the United States prior to publication of the rule in today's 
Federal Register. This rule is a ``major rule'' for purposes of SBREFA.

VIII. Response to Petition for Administrator Browner's Recusal

    On March 13, 1997, the Washington Legal Foundation (WLF), filed a 
petition with EPA asking that I, Carol Browner, disqualify myself in 
rulemaking regarding the NAAQS for PM and O3. The petition 
claims that my public statements indicate a ``clear and convincing 
showing'' that I had ``already decided to revise the NAAQS for PM and 
ozone'' and that I therefore ``could not give meaningful 
consideration'' to comments adverse to the proposed rule. On May 12, 
1997, EPA's General Counsel, Jonathan Z. Cannon, sent a letter to WLF 
regarding the petition. This letter and the WLF petition were then 
placed in the dockets for the proposed O3 and PM standards 
pending ``consideration and final response in connection with the 
Agency's final actions.''
    Contrary to WLF's assertions, I have maintained an open mind 
throughout these proceedings, and have based today's decisions on the 
rulemaking

[[Page 38894]]

record--including consideration of comments opposed to the proposal. 
The law does not require the Administrator of EPA to disqualify herself 
merely for expressing views on a proposed regulation; in fact, it is 
part of my responsibility to engage in the public debate on the 
proposals. Moreover, the assertions in WLF's petition do not accurately 
represent my views. The petition takes quotes out of context and 
repeatedly misinterprets my statements. For example, WLF quotes a 
statement that I made at the Children's Environmental Health Network 
Research Conference as an indication that I had ``prejudged the 
issue.'' However, my statement that ``I will not be swayed'' did not 
refer to adopting the NAAQS as proposed. Instead, as is clear from 
reviewing the entire speech, I was addressing my broader concern about 
children's health and the range of EPA standards affecting children's 
health. I also appeared at several congressional hearings and testified 
before members of Congress, some of whom were strongly opposed to the 
proposals. At those hearings, I explained the basis for the proposals 
and put forward the reasons why I concluded the proposals were 
appropriate, given the information before me at the time. At the same 
time, I made clear that I took very seriously my obligation to keep an 
open mind, and to consider fully and fairly all significant comments 
that the Agency received. For these reasons and others, as set forth in 
Mr. Cannon's May 12, 1997 response to WLF, which I adopt in full, I 
have decided not to recuse myself from any aspect of considering 
revisions to the NAAQS for O3 and PM. Accordingly, I am 
hereby denying WLF's petition.

IX. References

    (1) American Thoracic Society. (1985) Guidelines as to what 
constitutes an adverse respiratory health effect, with special 
reference to epidemiologic studies of air pollution. American Review 
of Respiratory Disease.. 131: 666-668.
    (2) Freas (1996) Ambient air quality relationships among 
alternative ozone air quality standards. Internal memorandum from 
Warren P. Freas to file, U.S. EPA, EMAD/OAQPS/OAR, RTP, NC, dated 
October 30, 1996. Docket No. A-95-58 Item II-B-6.
    (3) Freas (1997) Ambient air quality relationships for counties 
meeting alternative air quality standards. Internal memorandum from 
Warren P. Freas to file, U.S. EPA, EMAD/OAQPS/OAR, RTP, NC, dated 
July 1, 1997. Docket No. A-95-58 Item xxx.
    (4) Heck, Walter W. And Ellis B. Cowling. January, 1997. EM 
Journal. ``The Need for a Long Term Cumulative Secondary Ozone 
Standard - An Ecological Perspective.'' Air and Waste Management 
Association, Pittsburgh, PA.; pp. 23-33.
    (5) Johnson, T; Capel, J.; Mozier, J.; McCoy, M. (1996a) 
Estimation of ozone exposures experienced by outdoor children in 
nine urban areas using a probabilistic version of NEM. Prepared by 
IT/Air Quality Services for U.S. EPA, OAQPS; Research Triangle Park, 
NC, August.
    (6) Johnson, T.; Capel, J.; McCoy, M.; Mozier, J. (1996b) 
Estimation of ozone exposures experienced by outdoor workers in nine 
urban areas using a probabilistic version of NEM. Prepared by IT/Air 
Quality Services for U.S. EPA, OAQPS; Research Triangle Park, NC, 
August.
    (7) McClellan, R. O., (1989) Letter from Chairman of Clean Air 
Scientific Advisory Committee to the EPA Administrator, dated May 1, 
1989. EPA-SAB-CASAC-LTR-89-019.
    (8) Richmond (1997) Supplemental ozone exposure and health risk 
analyses. Internal memorandum from Harvey M. Richmond to Karen M. 
Martin, U.S. EPA, AQSSD/OAQPS/OAR, RTP, NC, dated February 11, 1997. 
Docket No. A-95-58 Item IV-A-1.
    (9) Seitz (1996) Revocation date for the existing 1-hour ozone 
standards. Internal memorandum from John S. Seitz to Mary D. 
Nichols, U.S. EPA, OAQPS/OAR, RTP, NC, dated November 20, 1996. 
Docket No. A-95-59 Item II-B-3.
    (10) Thurston, G.D.; Ito, K.; Kinney, P.L.; Lippmann, M. (1992) 
A multi-year study of air pollution and respiratory hospital 
admissions in three New York State metropolitan areas: results for 
1988 and 1989 summers. Journal of Exposure Analysis and 
Environmental Epidemiology. 2:429-450.
    (11) U.S. Department of Health and Human Services (1996) Vital 
and health statistics: current estimates from the national health 
interview survey, 1994. Hyattsville, MD: Public Health Service, 
National Center for Health Statistics; DHHS publication no. (PHS) 
96-278.
    (12) U.S. Environmental Protection Agency (1996a) Air quality 
criteria for Ozone and related photochemical oxidants. Research 
Triangle Park, NC: Office of Health and Environmental Assessment, 
Environmental Criteria and Assessment Office; EPA report nos. EPA/
600/AP-93/004a-c.
    (13) U.S. Environmental Protection Agency (1996b) Review of the 
national ambient air quality standards for ozone: assessment of 
scientific and technical information. OAQPS staff paper. Research 
Triangle Park, NC: Office of Air Quality Planning and Standards; EPA 
report no. EPA-452/R-96-007. Available from: NTIS, Springfield, VA; 
PB96-203435.
    (14) Whitfield, R.G.; Biller, W.F.; Jusko, M.J.; Keisler, J.M. 
(1996) A probabilistic assessment of health risks associated with 
short-term exposure to tropospheric ozone. Report prepared for U.S. 
EPA, OAQPS. Argonne National Laboratory; Argonne, IL, June. (For 
copies, contact Harvey M. Richmond, U.S. Environmental Protection 
Agency, OAQPS, MD-15, Research Triangle Park, N.C. 27711, (919) 541-
5271.)
    (15) Wolff, G. T., (1995a) Letter from Chairman of Clean Air 
Scientific Advisory Committee to the EPA Administrator, dated 
November 28, 1995. EPA-SAB-CASAC-LTR-96-001.
    (16) Wolff, G. T., (1995b) Letter from Chairman of Clean Air 
Scientific Advisory Committee to the EPA Administrator, dated 
November 30, 1995. EPA-SAB-CASAC-LTR-96-002.
    (17) Wolff, G. T., (1996) Letter from Chairman of Clean Air 
Scientific Advisory Committee to the EPA Administrator, dated April 
4, 1996. EPA-SAB-CASAC-LTR-96-006.

List of Subjects in 40 CFR Part 50

    Environmental protection, Air pollution control, Carbon monoxide, 
Lead, Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

    Dated: July 16, 1997.

Carol M. Browner,
Administrator.

    Therefore, for the reasons set forth in the preamble, title 40, 
chapter I, part 50 of the Code of Federal Regulations is amended as 
follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

    1. The authority citation for part 50 continues to read as follows:
    Authority: Secs. 109 and 301(a), Clean Air Act, as amended (42 
U.S.C. 7409, 7601(a)).


    2. Section 50.9 is revised to read as follows:


Sec. 50.9   National 1-hour primary and secondary ambient air quality 
standards for ozone.

    (a) The level of the national 1-hour primary and secondary ambient 
air quality standards for ozone measured by a reference method based on 
Appendix D to this part and designated in accordance with part 53 of 
this chapter, is 0.12 parts per million (235 g/m3). 
The standard is attained when the expected number of days per calendar 
year with maximum hourly average concentrations above 0.12 parts per 
million (235 g/m3) is equal to or less than 1, as 
determined by Appendix H to this part.
    (b) The 1-hour standards set forth in this section will no longer 
apply to an area once EPA determines that the area has air quality 
meeting the 1-hour standard. Area designations are codified in 40 CFR 
part 81.
    3. Section 50.10 is added to read as follows:


Sec. 50.10   National 8-hour primary and secondary ambient air quality 
standards for ozone.

    (a) The level of the national 8-hour primary and secondary ambient 
air quality standards for ozone, measured

[[Page 38895]]

by a reference method based on Appendix D to this part and designated 
in accordance with part 53 of this chapter, is 0.08 parts per million 
(ppm), daily maximum 8-hour average.
    (b) The 8-hour primary and secondary ozone ambient air quality 
standards are met at an ambient air quality monitoring site when the 
average of the annual fourth-highest daily maximum 8-hour average ozone 
concentration is less than or equal to 0.08 ppm, as determined in 
accordance with Appendix I to this part.
    4. Appendix D is amended by revising references 8 and 9 and by 
removing all of the text and figures immediately following ``Figure 2, 
Schematic Diagram of a Typical UV Photometric Calibration System 
(Option 1), through the end of Appendix D.

Appendix D to Part 50--Measurement Principle and Calibration 
Procedure for the Measurement of Ozone in the Atmosphere

*    *    *    *    *
    6. References.
*   *   *   *   *
    8. Transfer Standards for Calibration of Ambient Air Monitoring 
Analyzers for Ozone, EPA publication number EPA-600/4-79-056, EPA, 
National Exposure Research Laboratory, Department E, (MD-77B), 
Research Triangle Park, NC 27711.
    9. Technical Assistance Document for the Calibration of Ambient 
Ozone Monitors, EPA publication number EPA-600/4-79-057, EPA, 
National Exposure Research Laboratory, Department E, (MD-77B), 
Research Triangle Park, NC 27711.
*   *   *   *   *

 Appendix E [Removed and Reserved]

    5. Appendix E is removed and reserved.
    6. Appendix H is amended by revising the appendix heading to read 
``Appendix H To Part 50--Interpretation of The 1-Hour Primary and 
Secondary National Ambient Air Quality Standards for Ozone''.
    7. Appendix I is added to read as follows:

Appendix I to Part 50--Interpretation of the 8-Hour Primary and 
Secondary National Ambient Air Quality Standards for Ozone

     1.  General. 
    This appendix explains the data handling conventions and 
computations necessary for determining whether the national 8-hour 
primary and secondary ambient air quality standards for ozone 
specified in Sec. 50.10 are met at an ambient ozone air quality 
monitoring site. Ozone is measured in the ambient air by a reference 
method based on Appendix D of this part. Data reporting, data 
handling, and computation procedures to be used in making 
comparisons between reported ozone concentrations and the level of 
the ozone standard are specified in the following sections. Whether 
to exclude, retain, or make adjustments to the data affected by 
stratospheric ozone intrusion or other natural events is subject to 
the approval of the appropriate Regional Administrator.
     2.  Primary and Secondary Ambient Air Quality Standards for 
Ozone. 
    2.1  Data Reporting and Handling Conventions.
    2.1.1 Computing 8-hour averages. Hourly average concentrations 
shall be reported in parts per million (ppm) to the third decimal 
place, with additional digits to the right being truncated. Running 
8-hour averages shall be computed from the hourly ozone 
concentration data for each hour of the year and the result shall be 
stored in the first, or start, hour of the 8-hour period. An 8-hour 
average shall be considered valid if at least 75% of the hourly 
averages for the 8-hour period are available. In the event that only 
6 (or 7) hourly averages are available, the 8-hour average shall be 
computed on the basis of the hours available using 6 (or 7) as the 
divisor. (8-hour periods with three or more missing hours shall not 
be ignored if, after substituting one-half the minimum detectable 
limit for the missing hourly concentrations, the 8-hour average 
concentration is greater than the level of the standard.) The 
computed 8-hour average ozone concentrations shall be reported to 
three decimal places (the insignificant digits to the right of the 
third decimal place are truncated, consistent with the data handling 
procedures for the reported data.)
     2.1.2  Daily maximum 8-hour average concentrations. (a) There 
are 24 possible running 8-hour average ozone concentrations for each 
calendar day during the ozone monitoring season. (Ozone monitoring 
seasons vary by geographic location as designated in part 58, 
Appendix D to this chapter.) The daily maximum 8-hour concentration 
for a given calendar day is the highest of the 24 possible 8-hour 
average concentrations computed for that day. This process is 
repeated, yielding a daily maximum 8-hour average ozone 
concentration for each calendar day with ambient ozone monitoring 
data. Because the 8-hour averages are recorded in the start hour, 
the daily maximum 8-hour concentrations from two consecutive days 
may have some hourly concentrations in common. Generally, 
overlapping daily maximum 8-hour averages are not likely, except in 
those non-urban monitoring locations with less pronounced diurnal 
variation in hourly concentrations.
    (b) An ozone monitoring day shall be counted as a valid day if 
valid 8-hour averages are available for at least 75% of possible 
hours in the day (i.e., at least 18 of the 24 averages). In the 
event that less than 75% of the 8-hour averages are available, a day 
shall also be counted as a valid day if the daily maximum 8-hour 
average concentration for that day is greater than the level of the 
ambient standard.
    2.2  Primary and Secondary Standard-related Summary Statistic. 
The standard-related summary statistic is the annual fourth-highest 
daily maximum 8-hour ozone concentration, expressed in parts per 
million, averaged over three years. The 3-year average shall be 
computed using the three most recent, consecutive calendar years of 
monitoring data meeting the data completeness requirements described 
in this appendix. The computed 3-year average of the annual fourth-
highest daily maximum 8-hour average ozone concentrations shall be 
expressed to three decimal places (the remaining digits to the right 
are truncated.)
    2.3 Comparisons with the Primary and Secondary Ozone Standards. 
(a) The primary and secondary ozone ambient air quality standards 
are met at an ambient air quality monitoring site when the 3-year 
average of the annual fourth-highest daily maximum 8-hour average 
ozone concentration is less than or equal to 0.08 ppm. The number of 
significant figures in the level of the standard dictates the 
rounding convention for comparing the computed 3-year average annual 
fourth-highest daily maximum 8-hour average ozone concentration with 
the level of the standard. The third decimal place of the computed 
value is rounded, with values equal to or greater than 5 rounding 
up. Thus, a computed 3-year average ozone concentration of 0.085 ppm 
is the smallest value that is greater than 0.08 ppm.
    (b) This comparison shall be based on three consecutive, 
complete calendar years of air quality monitoring data. This 
requirement is met for the three year period at a monitoring site if 
daily maximum 8-hour average concentrations are available for at 
least 90%, on average, of the days during the designated ozone 
monitoring season, with a minimum data completeness in any one year 
of at least 75% of the designated sampling days. When computing 
whether the minimum data completeness requirements have been met, 
meteorological or ambient data may be sufficient to demonstrate that 
meteorological conditions on missing days were not conducive to 
concentrations above the level of the standard. Missing days assumed 
less than the level of the standard are counted for the purpose of 
meeting the data completeness requirement, subject to the approval 
of the appropriate Regional Administrator.
    (c) Years with concentrations greater than the level of the 
standard shall not be ignored on the ground that they have less than 
complete data. Thus, in computing the 3-year average fourth maximum 
concentration, calendar years with less than 75% data completeness 
shall be included in the computation if the average annual fourth 
maximum 8-hour concentration is greater than the level of the 
standard.
    (d) Comparisons with the primary and secondary ozone standards 
are demonstrated by examples 1 and 2 in paragraphs (d)(1) and (d) 
(2) respectively as follows:
    (1) As shown in example 1, the primary and secondary standards 
are met at this monitoring site because the 3-year average of the 
annual fourth-highest daily maximum 8-hour average ozone 
concentrations (i.e., 0.084 ppm) is less than or equal to 0.08 ppm. 
The data completeness requirement is also met because the average 
percent of days with valid ambient monitoring data is greater than

[[Page 38896]]

90%, and no single year has less than 75% data completeness.

             Example 1. Ambient monitoring site attaining the primary and secondary ozone standards             
----------------------------------------------------------------------------------------------------------------
                                                 1st Highest  2nd Highest  3rd Highest  4th Highest  5th Highest
                                      Percent    Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
               Year                  Valid Days   hour Conc.   hour Conc.   hour Conc.   hour Conc.   hour Conc.
                                                    (ppm)        (ppm)        (ppm)        (ppm)        (ppm)   
----------------------------------------------------------------------------------------------------------------
1993..............................         100%        0.092        0.091        0.090        0.088        0.085
----------------------------------------------------------------------------------------------------------------
1994..............................          96%        0.090        0.089        0.086        0.084        0.080
----------------------------------------------------------------------------------------------------------------
1995..............................          98%        0.087        0.085        0.083        0.080        0.075
================================================================================================================
    Average.......................          98%                                               0.084             
----------------------------------------------------------------------------------------------------------------

    (2) As shown in example 2, the primary and secondary standards 
are not met at this monitoring site because the 3-year average of 
the fourth-highest daily maximum 8-hour average ozone concentrations 
(i.e., 0.093 ppm) is greater than 0.08 ppm. Note that the ozone 
concentration data for 1994 is used in these computations, even 
though the data capture is less than 75%, because the average 
fourth-highest daily maximum 8-hour average concentration is greater 
than 0.08 ppm.

          Example 2. Ambient Monitoring Site Failing to Meet the Primary and Secondary Ozone Standards          
----------------------------------------------------------------------------------------------------------------
                                                 1st Highest  2nd Highest  3rd Highest  4th Highest  5th Highest
                                      Percent    Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8- Daily Max 8-
               Year                  Valid Days   hour Conc.   hour Conc.   hour Conc.   hour Conc.   hour Conc.
                                                    (ppm)        (ppm)        (ppm)        (ppm)        (ppm)   
----------------------------------------------------------------------------------------------------------------
1993..............................          96%        0.105        0.103        0.103        0.102        0.102
----------------------------------------------------------------------------------------------------------------
1994..............................          74%        0.090        0.085        0.082        0.080        0.078
----------------------------------------------------------------------------------------------------------------
1995..............................          98%        0.103        0.101        0.101        0.097        0.095
================================================================================================================
    Average.......................          89%                                               0.093             
----------------------------------------------------------------------------------------------------------------

    3.  Design Values for Primary and Secondary Ambient Air Quality 
Standards for Ozone. 
    The air quality design value at a monitoring site is defined as 
that concentration that when reduced to the level of the standard 
ensures that the site meets the standard. For a concentration-based 
standard, the air quality design value is simply the standard-
related test statistic. Thus, for the primary and secondary ozone 
standards, the 3-year average annual fourth-highest daily maximum 8-
hour average ozone concentration is also the air quality design 
value for the site.
[FR Doc. 97-18580 Filed 7-17-97; 8:45 am]
BILLING CODE 6560-50-F