[Federal Register Volume 59, Number 159 (Thursday, August 18, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-20042]


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[Federal Register: August 18, 1994]


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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 58

[FRL-4842-4]

 

Ambient Air Quality Surveillance Siting Criteria for Open Path 
Analyzers

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: The EPA proposes to amend provisions of part 58 of chapter I 
of title 40 of the Code of Federal Regulations to define the 
appropriate ambient air monitoring criteria for open path (long-path) 
analyzers. The proposed revisions to the Ambient Air Quality 
Surveillance regulations would define the siting requirements for open 
path analyzers used as State and Local Air Monitoring Stations (SLAMS), 
which includes both National Air Monitoring Stations (NAMS) and 
Photochemical Assessment Monitoring Stations (PAMS), as well as the 
quality assurance procedures for this technology. These changes will 
allow the ambient air monitoring community to effectively use open path 
monitoring data for regulatory purposes.

DATES: Comments must be received on or before September 19, 1994. 
Requests for public hearing must be received by September 2, 1994. If a 
hearing is held, comments must be received on or before 30 days from 
the conclusion of the hearing.

ADDRESSES: Comments should be submitted (in duplicate, if possible) to: 
Air Docket (LE-131), Attention: Docket Number A-93-44, U.S. 
Environmental Protection Agency, room M-1500, 401 M Street, SW., 
Washington, DC 20460.
    Public hearing: A public hearing will be held, if requested, in 
accordance with information provided in the DATES section of this 
proposal, to provide interested parties an opportunity for oral 
presentation of data, views, or arguments concerning the proposed 
revisions. If anyone contacts EPA requesting a public hearing, it will 
be held at the EPA's Environmental Research Center, Research Triangle 
Park, North Carolina. Persons interested in attending the hearing or 
wishing to present oral testimony should notify Ms. Lee Ann B. Byrd, 
Monitoring and Reports Branch (MD-14), U.S. Environmental Protection 
Agency, Research Triangle Park, North Carolina 27711, telephone number 
(919) 541- 5367. Specific dates and other pertinent details of this 
public hearing will be published in a separate Federal Register notice.
    Docket: Docket Number A-93-44, containing supporting information 
used in developing these revised regulations, is available for public 
inspection and copying between 8:30 a.m. and 12 noon, and between 1:30 
p.m. and 3:30 p.m., Monday through Friday, at EPA's Air Docket Section 
at the address noted above. As provided in 40 CFR Part 2, a reasonable 
fee may be charged for copying.

FOR FURTHER INFORMATION CONTACT: Ms. Lee Ann B. Byrd at telephone (919) 
541-5367 concerning this action. The address is Monitoring and Reports 
Branch (MD-14), U.S. Environmental Protection Agency, Research Triangle 
Park, North Carolina 27711.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Authority
II. Background of Proposed Rule
III. Discussion of Proposed Revisions to Regulation
    A. Section 58.1 Definitions
    B. Appendix A--Quality Assurance Requirements for State and 
Local Air Monitoring Stations (SLAMS)
    C. Appendix B--Quality Assurance Requirements for Prevention of 
Significant Deterioration (PSD) Air Monitoring
    D. Appendix E--Probe and Path Siting Criteria for Ambient Air 
Quality Monitoring
IV. Comments and the Public Docket
V. Administrative Requirements
    A. Administrative Designation.
    B. Reporting and Recordkeeping Requirements
    C. Regulatory Flexibility Act

I. Authority

    Authority: sections 110, 301(a), 313, and 319 of the Clean Air 
Act as amended 42 U.S.C. 7410, 7601(a), 7613, 7619.

II. Background of Proposed Rule

    The Clean Air Act, as amended in 1990, requires, in sections 
181(b)(2), 185A, and 186(b)(2)(A), ambient air quality monitoring for 
purposes of defining areas of nonattainment with the National Ambient 
Air Quality Standards (NAAQS), evaluating progress toward achievement 
of the NAAQS pursuant to State implementation plans (SIP's), and 
reporting air quality data to the EPA to document the status and trends 
of the Nation's air quality. These are nontrivial activities, and to 
achieve the aforementioned objectives, the EPA must ensure that the 
ambient air monitoring networks consist of high quality instruments 
that produce accurate concentration measurements. As new monitoring 
techniques are developed, the EPA evaluates the new methodology and, as 
appropriate, determines how to effectively incorporate it into the 
existing air quality monitoring program. To assess new ambient air 
monitoring instruments for those pollutants with established NAAQS, the 
EPA currently uses the Ambient Air Monitoring Reference and Equivalent 
Method regulatory procedures detailed in title 40, chapter 1, part 53. 
The EPA does not formally regulate the performance testing of ambient 
air monitoring instruments, which measure pollutants without 
established NAAQS. Methodology for collected ozone (O3) precursor 
data (specified in the Photochemical Assessment Monitoring program as 
volatile organic compounds and oxides of nitrogen) is reviewed in the 
``Technical Assistance Document for Sampling and Analysis of Ozone 
Precursors,'' and any subsequent revisions, EPA/600-8-91/215, October 
1991. Supplementing the part 53 performance requirements and the 
aforementioned ``Technical Assistance Document,'' the part 58 Ambient 
Air Quality Surveillance regulation specifies how to most appropriately 
conduct routine ambient air monitoring through pollutant-specific 
monitor siting criteria, operation schedules, monitoring network 
design, and data reporting. Under the part 58 provisions, each SLAMS 
must employ reference or equivalent methods, as determined according to 
part 53, and meet all applicable siting requirements as contained in 
part 58, before its data can be used for regulatory purposes. 
Specifically, these regulatory actions include comparison with the 
NAAQS and other SIP-related activities. It is important to note that 
the NAMS and the PAMS are subsets of the SLAMS networks; therefore, 
provisions for the SLAMS also apply to both the NAMS and PAMS, as 
included in this proposal.
    A new technique for monitoring pollutants in ambient air has been 
developed and introduced to the EPA. Instruments based on this new 
technique, called open path (or long-path) analyzers, use ultraviolet, 
visible, or infrared light to measure nitrogen dioxide (NO2), 
O3, carbon monoxide (CO), sulfur dioxide (SO2), and other 
gaseous pollutant concentrations over a path of several meters up to 
several kilometers. The concentration measurements obtained by these 
open path analyzers are path-integrated, or path-averaged, values. 
Traditional fixed point analyzers measure pollutant concentrations at 
one specific point by extracting an air sample from the atmosphere 
through an inlet probe. A list of all EPA-approved reference and 
equivalent ambient air monitoring methods is available through the 
docket. Due to the fundamental difference in the measurement principles 
of open path and point analyzers, there may be trade-offs in using each 
type of instrument for certain applications. Because of the ability of 
open path analyzers to measure pollutant concentrations over a path, 
these new techniques are expected to provide better spatial coverage, 
and thereby a better assessment of a general population's exposure to 
air pollutants for certain applications. However, due to this same 
path-averaging characteristic, open path analyzers could underestimate 
high pollutant concentrations at specific points within the measurement 
path for other ambient air monitoring situations. The applicability of 
either technique to a particular monitoring scenario is dependent on a 
number of factors including plume dispersion characteristics, 
monitoring location, pollutant of interest, population density, site 
topography, and monitoring objective. The EPA has considered these 
factors in evaluating the advantages and disadvantages of using open 
path analyzers for the various ambient air monitoring applications 
detailed in 40 CFR part 58. Additionally, several studies of the 
comparability of data collected with point and open path analyzers have 
been conducted by the EPA and by other organizations. The most recent 
EPA study of these two methodologies was completed during the summer of 
1993 in Baytown, Texas. Results from this study and others are 
available in the docket for public review. The EPA solicits comment on 
these studies and on the comparability of using path-averaged and point 
measurements in the Nation's ambient air monitoring programs.
    The EPA is currently assessing the performance of an open path 
analyzer as a candidate method under part 53 to determine if it should 
be designated as an equivalent method for one or more of those 
pollutants. In parallel with this effort, the EPA has developed the 
appropriate part 58 siting and quality assurance criteria for open path 
analyzers, which are contained in this proposal.
    The existing part 58 monitoring network design criteria define the 
monitoring objectives for a particular site in terms of measurement 
scale. More specifically, each ambient air monitoring station is 
located in such a way that it represents a particular air parcel or 
volume. The regulation uses six measurement scales to describe the size 
of these air parcels. These six scales are: microscale (dimensions of 
several meters to approximately 100 meters), middle scale (100 to 500 
meters), neighborhood scale (500 meters to 4 kilometers), urban scale 
(4 to 50 kilometers), regional scale (tens to hundreds of kilometers), 
and national or global scales. (National and global scales are 
generally not applicable for a single air monitoring station. National 
and global averages are more appropriately determined by networks of 
various monitoring stations.) Within each of these measurement scales, 
it is assumed that the pollutant concentrations are relatively 
homogeneous; therefore, a monitor placed at any point in the area, 
within the tolerances of this siting regulation, measures a 
concentration representative of that area.
    Depending on the objective for a particular SLAMS, each pollutant 
can be monitored on a particular measurement scale as defined in Table 
5 of appendix D in part 58. The applicability of the first five scales 
to monitoring the four pollutants referenced in this proposal, CO, 
NO2, O3, and SO2, follows:

              Summary of Spatial Scales for Selected SLAMS              
------------------------------------------------------------------------
                                                               Ozone    
      Measurement Scale         CO     NO2    O3     SO2   precursors\1\
------------------------------------------------------------------------
Micro-.......................  Yes..  No...  No...  No...  No.          
scale........................                                           
Middle scale.................  Yes..  Yes..  Yes..  Yes..  No.          
Neighborhood scale...........  Yes..  Yes..  Yes..  Yes..  Yes.         
Urban scale..................  No...  Yes..  Yes..  Yes..  Yes.         
Regional.....................  No...  No...  Yes..  Yes..  No.          
------------------------------------------------------------------------
\1\Ozone precursors, as defined in the PAMS program, include volatile   
  organic compounds, oxides of nitrogen, and selected carbonyls.        

    Existing regulations in part 58 state that the pollutant 
concentration within a particular measurement scale is nearly 
homogeneous, and that a point measurement collected in this same scale 
generally represents any other point within that scale. This basic 
provision defines how ambient air monitoring data can be used to 
represent the air quality in a neighborhood, city, or other geographic 
region. Based on these current provisions, it is reasonable to accept 
that a path-averaged measurement taken within the dimensions and other 
siting specifications of that measurement scale would provide a value 
descriptive of that same geographic region. In order to maintain data 
comparability between open path and point analyzers, the revisions 
contained in this proposal are based on the siting criteria currently 
being used with conventional fixed point ambient air monitoring 
networks. The most obvious difference between the proposed and existing 
siting criteria is that the new requirements are defined in terms of a 
``probe'' (applicable to point analyzers), a ``monitoring path'' 
(applicable to open path analyzers), or both. Some minor flexibility in 
siting criteria was added for open path analyzers to compensate for the 
additional difficulties in locating suitable sites for the various 
equipment used with an open path analyzer, such as retroreflectors, 
receivers, and transmitters. Nonetheless, these criteria should still 
provide a concentration representative of the area to be monitored.
    It is important to note that criteria for open path measurement of 
CO in a street canyon scenario, typically defined in terms of 
microscale dimensions (up to 100 meters), is not included in this 
proposal. The siting criteria currently used for microscale CO 
monitoring is unique and narrow in scope in comparison to other 
monitoring scenarios. Adapting the existing siting criteria to 
accommodate path measurement techniques, as this proposal does for 
other types of monitoring scales, would unduly restrict the usage of 
open path analyzers for this particular application. In order to fully 
address more appropriate siting criteria for microscale CO monitoring 
using open path analyzers, the EPA must more fully evaluate the effects 
of measuring path-averaged CO concentrations across roadways, 
intersections, and at locations other than those currently defined in 
the part 58 regulation. The EPA specifically solicits comments from the 
public regarding the use of open path analyzers for measuring CO in 
microscale applications.

III. Discussion of Proposed Revisions to Regulations

A. Section 58.1  Definitions

    Today's proposal would amend the definitions section of part 58 by 
adding several new definitions that are necessary to clearly define the 
proposed new requirements for open path analyzers. Definitions for 
``point analyzer'' and ``open path analyzer'' would be added to define 
these two types of automated instruments and to clarify the distinction 
between them, since the various new and existing requirements may apply 
to one or the other or both types of analyzers. A new definition for 
``probe'' is proposed to specify the inlet where an air sample is 
extracted from the atmosphere for delivery to a sampler or point 
analyzer. This definition would clarify that location requirements 
applicable to point analyzers apply to the analyzer's probe and not to 
the analyzer (or sampler) itself, which could be located some distance 
from the probe. Similarly, a new definition is proposed for 
``monitoring path'' to describe the path in the atmosphere over which 
an open path analyzer measures and averages a pollutant concentration. 
Closely associated with the term ``monitoring path'' are new 
definitions for ``monitoring path length,'' to describe the scalar 
length of the monitoring path, and ``optical measurement path length,'' 
to describe the actual length of the optical beam of an open path 
instrument. The length of the optical beam may be two or more times the 
length of the monitoring path when one or more mirrors are used to 
cause the optical beam to pass through the monitoring path more than 
once.
    To help describe the new requirements for data quality assessment 
procedures, the term ``effective concentration'' is proposed. It would 
refer to the ambient concentration of a pollutant over the monitoring 
path that would be equivalent to a much higher concentration of the 
pollutant contained in a short calibration cell inserted into the 
optical beam of an open path analyzer during a precision test or 
accuracy audit. Specifically, effective concentration is proposed to be 
defined as the actual concentration of the pollutant in the test cell 
multiplied by the ratio of the optical measurement path length of the 
test cell to the optical measurement path length of the atmospheric 
monitoring path. Also, when a calibration cell is inserted into the 
actual atmospheric measurement beam of an open path analyzer for a 
precision or accuracy test, the resulting measurement reading would be 
the sum of the pollutant concentration in the calibration cell and the 
pollutant concentration in the atmosphere. The atmospheric pollutant 
concentration must be measured separately and subtracted from the test 
measurement to produce a ``corrected concentration,'' which would be 
the true test result. Thus, the term ``corrected concentration'' is 
proposed to define the result of such a precision or accuracy 
assessment test after correction of the test measurement by subtracting 
the atmospheric pollutant concentration.
    Finally, a formal definition of ``monitor'' is proposed to clarify 
its use in the regulations as a generic term to refer to any type of 
ambient air analyzer or sampler that is acceptable for use in a SLAMS 
monitoring network under Appendix C of this part. A monitor could thus 
be a point analyzer, an open path analyzer, or a sampler.

B. Appendix A--Quality Assurance Requirements for State and Local Air 
Monitoring Stations (SLAMS)

    Appendix A sets forth both general quality assurance requirements 
applicable to SLAMS air monitoring as well as specific procedures for 
assessing the quality of the monitoring data obtained in SLAMS 
monitoring networks. While the general quality assurance requirements 
(in section 2) would be directly applicable to open path analyzers 
without change, the more specific data quality assessment procedures 
(in section 3) must be modified somewhat to apply to open path 
analyzers. Accordingly, changes to these procedures are proposed to 
incorporate appropriate data quality assessment tests applicable to 
open path monitoring instruments. To the extent possible, the new 
requirements are similar or parallel to the existing requirements for 
point analyzers.
    For both the precision test (Sec. 3.1) and the accuracy audit 
(Sec. 3.2), the proposed new requirements specify that an optical 
calibration or test cell containing a pollutant concentration standard 
must be inserted into the optical measurement beam of the open path 
analyzer. Both theory and testing indicate that the use of such a 
calibration or test cell is equivalent in accuracy to measurement of 
the equivalent pollutant concentration in air over the entire 
monitoring path of an open path analyzer. Each concentration standard 
must be selected such that it produces an ``effective concentration'' 
equivalent to a specified ambient concentration over the monitoring 
path. As noted previously, effective concentration is defined as the 
actual concentration of the pollutant in the test cell multiplied by 
the ratio of the optical measurement path length of the test cell to 
the optical measurement path length of the atmospheric monitoring path. 
The effective concentrations specified for the precision and accuracy 
tests for open path analyzers would be the same as the test 
concentrations currently specified in these procedures for point 
analyzers.
    Ideally, precision and accuracy assessments should test a 
monitoring instrument in its normal monitoring configuration. 
Therefore, the proposed test procedures require that the test or 
calibration cell containing the test pollutant concentration standard 
be inserted into the actual atmospheric measurement beam of the open 
path analyzer. The resulting test measurement of the pollutant 
concentration would thus be the sum of the test concentration in the 
cell and the pollutant concentration in the atmosphere, because the 
measurement beam would pass through both the test cell and the 
atmospheric monitoring path. Accordingly, a correction for the 
atmospheric concentration is required to obtain the true test result. 
In the proposed procedures, the atmospheric pollutant concentration 
would be measured immediately before and again immediately after the 
precision or accuracy test, and the average of these two measurements 
would be subtracted from the test concentration measurement to produce 
a ``corrected concentration,'' which would be reported as the test 
result.
    The corrected concentration reported for a precision or accuracy 
test may not be accurate if the atmospheric pollutant concentration 
changes during the test. When the ambient concentration is variable, 
the average of the pre- and post-test measurements may not be an 
accurate representation of the ambient pollutant concentration during 
the test. The proposed test procedures recommend that these tests 
should be carried out, if possible, during periods when the atmospheric 
pollutant concentration is low and steady. The lower the atmospheric 
pollutant concentration, the steadier the concentration is likely to be 
and the better the pre- and post-test measurements will represent the 
actual atmospheric concentration during the test measurement. Further, 
the procedures propose that if the pre- and post-test measurements of 
the atmospheric concentration differ by more that 20 percent of the 
effective concentration of the test standard, the test result would be 
discarded and the test repeated.
    It is recognized that the proposed tests for precision and accuracy 
for open path analyzers, as well as the existing tests for point 
analyzers, are described in very general terms, and that additional, 
more detailed information and guidance is usually necessary for an 
analyzer operator to carry out these tests properly. Accordingly, 
section 3 of appendix A is proposed to be amended by adding an explicit 
indication that supplemental information and guidance to assist the 
analyst in conducting these tests may be available in the publication, 
``Quality Assurance Handbook for Air Pollution Measurement Systems, 
Volume II'' (EPA-600/4-77-027a, identified as Reference 3 at the end of 
Appendix A), or in the operation or instruction manual associated with 
the particular monitor being used.
    The proposed techniques for precision and accuracy assessment of 
open path analyzers are based largely on consultations with the 
manufacturer, along with EPA tests, of the differential optical 
absorption spectrometer that is currently under consideration by EPA 
for possible designation as equivalent methods under 40 CFR part 53. 
However, it is desirable that the techniques be generic in nature, if 
possible, so that they would be applicable to other types of open path 
monitoring instruments as well. In addition, for some types of open 
path instruments or for some installations or configurations, there may 
be technical reasons why the proposed techniques for precision and 
accuracy assessment may not be feasible, appropriate, or advisable. The 
procedures, as currently proposed, allow for the use of an alternate 
local light source or an alternate optical path that does not include 
the normal atmospheric monitoring path, if such alternate configuration 
is permitted by the operation or instruction manual associated with the 
analyzer. Since the analyzer operation or instruction manual would be 
subject to approval as part of the requirements for EPA designation of 
an open path analyzer as an equivalent method, EPA would thereby have 
control over the alternate configurations that would be allowable for 
the precision and accuracy assessment tests.
    In view of these issues regarding the precision and accuracy 
assessment techniques, EPA specifically solicits comments on: (1) The 
suitability of the proposed techniques; (2) the advisability of a 
technique that requires correction of the test result for the 
atmospheric pollutant concentration versus a technique that does not 
require that correction but does not test the normal atmospheric 
measurement components and configuration; (3) the proposed technique 
for correcting test measurements for the atmospheric pollutant 
concentration, if required, and the 20 percent limit on the difference 
between the pre- and post-test measurements of the atmospheric 
concentration; and (4) whether the proposed techniques are sufficiently 
generic in nature to apply to various other types of open path 
analyzers that might be applicable to SLAMS monitoring, or how the 
techniques could be made more generic.

C. Appendix B--Quality Assurance Requirements for Prevention of 
Significant Deterioration (PSD) Air Monitoring

    Appendix B sets forth both general quality assurance requirements 
for PSD monitoring as well as specific procedures for assessing the 
quality of the monitoring data obtained in PSD monitoring networks. The 
amendments and procedures proposed for Appendix B to extend the 
existing requirements to open path analyzers are essentially identical 
to the changes proposed for Appendix A.

D. Appendix E--Probe and Path Siting Criteria for Ambient Air Quality 
Monitoring

    This proposal would amend Appendix E by adding new siting criteria 
applicable to open path analyzers for monitoring of SO2, O3, 
NO2, CO, and O3 precursors (defined in the PAMS program as 
volatile organic compounds, oxides of nitrogen, and selected 
carbonyls). Because of the substantial similarity in the siting 
criteria for SO2, O3, and NO2 (both the existing 
criteria for point monitors and proposed new criteria for open path 
analyzers), the siting requirements for these three pollutants are 
proposed to be combined, consolidated, and set forth in section 2 of 
appendix E. The existing criteria for SO2, O3, and NO2 
in sections 3, 5, and 6 would be deleted, and those sections would be 
reserved. As noted below, the criteria for CO monitoring are somewhat 
different, so they would be retained in a separate section 4. Siting 
criteria for measuring O3 and its precursors as part of a PAMS 
network are included in section 10. In all cases, the new open path 
provisions would be incorporated into the existing provisions, as 
appropriate.
    The proposed new open path siting requirements largely parallel the 
existing requirements for point analyzers, with the revised provisions 
applicable to either a ``probe'' (for point analyzers), a ``monitoring 
path'' (for open path analyzers), or both, as appropriate. Accordingly, 
criteria for the monitoring path of an open path analyzer are proposed 
for horizontal and vertical placement, spacing from minor sources, 
spacing from obstructions, spacing from trees, and spacing from 
roadways. The open path requirements would apply to most of the 
monitoring path--generally 80 or 90 percent--but not to the entire 
monitoring path, to allow some needed flexibility in siting open path 
analyzers. For example, using the proposed 80 percent requirement, a 
monitoring path may be sited across uneven terrain, where up to 20 
percent of the monitoring path may not fall within the proposed 3 to 15 
meter specification for height above ground.
    In addition to the criteria common to both point and open path 
analyzers mentioned above, two new provisions, applicable only to open 
path analyzers, would limit the maximum length of the monitoring path 
and the cumulative interferences on the path. The maximum monitoring 
path length limit would help to ensure that open path monitoring data 
represent the air volume that they are intended to measure according to 
the monitoring objectives of the spatial scale identified for the site. 
Similarly, the limit for the cumulative interferences on the monitoring 
path would control the total amount of interferences from minor 
sources, roadways, obstructions, and other factors that might unduly 
influence the monitoring data collected by an open path analyzer. This 
limit is necessary because a long monitoring path presents a much 
greater opportunity to be affected by multiple interferences. It is 
also recognized that State or local air monitoring agencies may 
encounter difficulties in locating atmospheric monitoring equipment due 
to vandalism, scarcity of available sites, and other considerations; 
therefore, certain provisions are included in both the existing and the 
proposed new provisions of the regulation to accommodate these 
difficulties.
    In the consolidation of current sections 3, 5, and 6 to section 2, 
Tables 2 and 3, which list the minimum separation distance between 
O3 and NO2 stations and nearby roadways, would be combined 
and redesignated as Table 1. As a result, Table 1 (in section 3), Table 
4 (in section 7), Table 5 (in section 10), and Table 6 (in section 12) 
would be renumbered as tables 2, 3, 4, and 5, respectively. Finally, 
the summary of all the general siting requirements in renumbered Table 
5 would be modified to include the new criteria for monitoring paths.

IV. Comments and the Public Docket

    The EPA welcomes comments on all aspects of this proposed 
rulemaking, specifically: (a) The appropriateness of using open path 
(long-path) analyzers to measure CO, O3, SO2, NO2, and/
or O3 precursors (defined in the PAMS program as volatile organic 
compounds, oxides of nitrogen, and selected carbonyls); (b) the ability 
of a monitoring agency to use an open path analyzer in a manner 
consistent with these siting criteria; (c) using open path analyzers to 
measure CO in microscale scenarios; (d) the precision and accuracy 
assessment techniques as described in the proposed Appendix A and 
Appendix B regulations; (e) using open path analyzers to measure 
SO2 in source-oriented ambient air monitoring networks, 
particularly in micro- and middle-scale applications; and (f) all 
available and relevant study information on the comparability of open 
path and point ambient air monitoring. All comments, with the exception 
of proprietary information, should be directed to the EPA Air Docket 
Section, Docket No. A-93-44.
    Those who wish to submit proprietary information for consideration 
should clearly separate such information from other comments by:
     Labeling proprietary information ``Confidential Business 
Information,'' and;
     Sending proprietary information directly to the contact 
person listed (see FOR FURTHER INFORMATION CONTACT) and not to the 
public docket.
    This will help ensure that proprietary information is not 
inadvertently placed in the docket. If a commenter wants the EPA to use 
a submission labeled as confidential business information as part of 
the basis for the final rule, then a nonconfidential version of the 
document, which summarizes the key data or information, should be sent 
to the docket.
    Information covered by a claim of confidentiality will be disclosed 
by the EPA only to the extent allowed and by the procedures set forth 
in 40 CFR part 2. If no claim of confidentiality accompanies the 
submission when it is received by the EPA, the submission may be made 
available to the public without notifying the commenters.

V. Administrative Requirements

A. Administrative Designation

Executive Order 12866
    Under Executive Order 12866 (58 FR 51735 (October 4, 1993)) the 
Agency must determine whether the regulatory action is ``significant'' 
and therefore subject to Office of Management and Budget (OMB) review 
and the requirements of the Executive Order. The Order defines 
``significant regulatory action'' as one 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 or recipients 
thereof; or
    (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.
    It has been determined that this rule is not a ``significant 
regulatory action'' under the terms of Executive Order 12866 and is 
therefore not subject to OMB review.

B. Reporting and Recordkeeping Requirements

    All of the information collection requirements contained in part 58 
have been approved by the OMB under the Paperwork Reduction Act of 
1980, 44 U.S.C. 3501 et seq., and have been assigned OMB Control Number 
2060-0084. This proposed amendment to Part 58 does not add any new 
information collection requirements.

C. Regulatory Flexibility Act

    Pursuant to section 605(b) of the Regulatory Flexibility Act, 5 
U.S.C. 605(b), the Administrator certifies that this rule will not have 
a significant economic impact on a substantial number of small 
entities. This rulemaking package does not impose any additional 
requirements on small entities, rather, it is this proposal's intent to 
provide all entities with the option to choose the most suitable 
ambient air method for their particular application. This proposal 
provides the appropriate siting and quality assurance criteria for a 
new ambient air monitoring technology (open path analyzers) as they are 
used in various applications. All of the criteria listed in this 
rulemaking package parallel existing requirements and vary only as 
necessary due to technological differences between measurement 
techniques. It is possible that a beneficial impact may be encountered 
by some small entities that use this new technology in certain 
scenarios.

List of Subjects in 40 CFR Part 58

    Air pollution control, Ambient air monitoring, Ambient air 
monitoring networks and siting criteria, Intergovernmental relations, 
National ambient air monitoring program, Quality assurance 
requirements, Reporting and recordkeeping requirements, State and local 
agency ambient air monitoring programs.

    Dated: August 4, 1994.
Carol M. Browner,
Administrator.

    For reasons set forth in the preamble, title 40, chapter I, part 58 
of the Code of Federal Regulations is proposed to be amended as 
follows:

PART 58--[AMENDED]

    1. The authority citation for part 58 continues to read as follows:

    Authority: 42 U.S.C. 7410, 7601(a), 7613, and 7619.

    2. In Sec. 58.1, the following definitions are added:


Sec. 58.1  Definitions.

* * * * *
    (z) Point analyzer is an automated analytical method that measures 
pollutant concentration in an ambient air sample extracted from the 
atmosphere at a specific inlet probe point and that has been designated 
as a reference or equivalent method in accordance with part 53 of this 
chapter.
    (aa) Probe is the actual inlet where an air sample is extracted 
from the atmosphere for delivery to a sampler or point analyzer for 
pollutant analysis.
    (bb) Open path analyzer is an automated analytical method that 
measures the average atmospheric pollutant concentration in situ along 
one or more monitoring paths having a monitoring path length of 5 
meters or more and that has been designated as a reference or 
equivalent method under the provisions of part 53 of this chapter.
    (cc) Monitoring path for an open path analyzer is the actual path 
in space over which the pollutant concentration is measured and 
averaged.
    (dd) Monitoring path length of an open path analyzer is the length 
of the monitoring path in the atmosphere over which the average 
pollutant concentration measurement is determined. See also, ``optical 
measurement path length.''
    (ee) Optical measurement path length is the actual length of the 
optical beam over which measurement of the pollutant is determined. 
Generally, the optical measurement path length is:
    (1) Equal to the monitoring path length for a (bistatic) system 
having transmitter and receiver at opposite ends of the monitoring 
path;
    (2) Equal to twice the monitoring path length for a (monostatic) 
system having a transmitter and receiver at one end of the monitoring 
path and a mirror or retroreflector at the other end; or
    (3) Equal to some multiple of the monitoring path length for more 
complex systems having multiple passes of the measurement beam through 
the monitoring path.
    (ff) Effective concentration pertains to testing an open path 
analyzer with a high-concentration calibration or audit standard gas 
contained in a short test cell inserted into the optical measurement 
beam of the instrument. Effective concentration is the equivalent 
ambient-level concentration that would produce the same spectral 
absorbance over the actual atmospheric monitoring path length as 
produced by the high-concentration gas in the short test cell. 
Quantitatively, effective concentration is equal to the actual 
concentration of the gas standard in the test cell multiplied by the 
ratio of the path length of the test cell to the actual atmospheric 
monitoring path length.
    (gg) Corrected concentration pertains to the result of an accuracy 
or precision assessment test of an open path analyzer in which a high-
concentration test or audit standard gas contained in a short test cell 
is inserted into the optical measurement beam of the instrument. When 
the pollutant concentration measured by the analyzer in such a test 
includes both the pollutant concentration in the test cell and the 
concentration in the atmosphere, the atmospheric pollutant 
concentration must be subtracted from the test measurement to obtain 
the corrected concentration test result. The corrected concentration is 
equal to the measured concentration minus the average of the 
atmospheric pollutant concentrations measured (without the test cell) 
immediately before and immediately after the test.
    (hh) Monitor is a generic term for an instrument, sampler, 
analyzer, or other device that measures or assists in the measurement 
of atmospheric air pollutants and is acceptable for use in ambient air 
surveillance under the provisions of appendix C to this part, including 
both point and open path analyzers that have been designated as 
reference or equivalent methods under part 53 of this chapter and air 
samplers that are specified as part of a manual method that has been 
designated as a reference or equivalent method under part 53 of this 
chapter.

Appendix A [Amended]

    3. Appendix A is amended as follows:
    a. The fourth paragraph of section 3 introductory text is revised.
    b. Section 3.1 is revised.
    c. The text preceding the table in the second paragraph, and the 
seventh, and eighth paragraphs of Sec. 3.2 are revised; and a new 
paragraph is added between the seventh and eighth paragraphs.
    d. Table A-1 is revised.

Appendix A--Quality Assurance Requirements for State and Local Air 
Monitoring Stations (SLAMS)

* * * * *

3. Data Quality Assessment Requirements

* * * * *
    Assessment results shall be reported as specified in section 4. 
Concentration and flow standards must be as specified in Secs. 2.3 
or 3.4. In addition, working standards and equipment used for 
accuracy audits must not be the same standards and equipment used 
for routine calibration. Additional information and guidance in the 
technical aspects of conducting these tests may be found in 
Reference 3 or in the operation or instruction manual associated 
with the analyzer or sampler. Concentration measurements reported 
from analyzers or analytical systems (indicated concentrations) 
should be based on stable readings and must be derived by means of 
the same calibration curve and data processing system used to obtain 
the routine air monitoring data (see Reference 1 and Reference 3, 
section 2.0.9.1.3(d)). Table A-1 provides a summary of the minimum 
data quality assessment requirements, which are described in more 
detail in the following sections.

3.1  Precision of Automated Methods

    A one-point precision check must be carried out at least once every 
2 weeks on each automated analyzer used to measure SO2, NO2, 
O3, and CO. The precision check is made by challenging the 
analyzer with a precision check gas of known concentration (effective 
concentration for open path analyzers) between 0.08 and 0.10 ppm for 
SO2, NO2, and O3 analyzers, and between 8 and 10 ppm for 
CO analyzers. To check the precision of SLAMS analyzers operating on 
ranges higher than 0 to 1.0 ppm SO2, NO2, and O3, or 0 
to 100 ppm for CO, use precision check gases of appropriately higher 
concentration as approved by the appropriate Regional Administrator or 
the Regional Administrator's designee. However, the results of 
precision checks at concentration levels other than those specified 
above need not be reported to the EPA. The standards from which 
precision check test concentrations are obtained must meet the 
specifications of Sec. 2.3.
    Except for certain CO analyzers described below, point analyzers 
must operate in their normal sampling mode during the precision 
check, and the test atmosphere must pass through all filters, 
scrubbers, conditioners, and other components used during normal 
ambient sampling and as much of the ambient air inlet system as is 
practicable. If permitted by the associated operation or instruction 
manual, a CO point analyzer may be temporarily modified during the 
precision check to reduce vent or purge flows, or the test 
atmosphere may enter the analyzer at a point other than the normal 
sample inlet, provided that the analyzer's response is not likely to 
be altered by these deviations from the normal operational mode.
    If a precision check is made in conjunction with a zero or span 
adjustment, it must be made prior to such zero or span adjustments. 
Randomization of the precision check with respect to time of day, 
day of week, and routine service and adjustments is encouraged where 
possible.
    Open path analyzers are tested by inserting a test cell 
containing a precision check gas concentration into the optical 
measurement beam of the instrument. If possible, the normally used 
transmitter, receiver, and, as appropriate, reflecting devices 
should be used during the test, and the normal monitoring 
configuration of the instrument should be altered as little as 
possible to accommodate the test cell for the test. However, if 
permitted by the associated operation or instruction manual, an 
alternate local light source or an alternate optical path that does 
not include the normal atmospheric monitoring path may be used. The 
actual concentration of the precision check gas in the test cell 
must be selected to produce an ``effective concentration'' in the 
range specified above. Generally, the precision test concentration 
measurement will be the sum of the atmospheric pollutant 
concentration and the precision test concentration. If so, the 
result must be corrected to remove the atmospheric concentration 
contribution. The ``corrected concentration'' is obtained by 
subtracting the average of the atmospheric concentrations measured 
by the instrument immediately before and immediately after the 
precision check test from the precision test concentration 
measurement. If the difference between these before and after 
measurements is greater than 20 percent of the effective 
concentration of the test gas, discard the test result and repeat 
the test. If possible, open path analyzers should be tested during 
periods when the atmospheric pollutant concentrations are relatively 
low and steady.
    Report the actual concentration (effective concentration for 
open path analyzers) of the precision check gas and the 
corresponding concentration measurement (corrected concentration, if 
applicable, for open path analyzers) indicated by the analyzer. The 
percent differences between these concentrations are used to assess 
the precision of the monitoring data as described in Sec. 5.1.

3.2  Accuracy of Automated Methods

* * * * *
    The audit is made by challenging the analyzer with at least one 
audit gas of known concentration (effective concentration for open 
path analyzers) from each of the following ranges that fall within 
the measurement range of the analyzer being audited:
* * * * *
    For point analyzers, the audit shall be carried out by allowing 
the analyzer to analyze the audit test atmosphere in its normal 
sampling mode such that the test atmosphere passes through all 
filters, scrubbers, conditioners, and other sample inlet components 
used during normal ambient sampling and as much of the ambient air 
inlet system as is practicable. The exception given in Sec. 3.1 for 
certain CO analyzers does not apply for audits.
    Open path analyzers are audited by inserting a test cell 
containing the various audit gas concentrations into the optical 
measurement beam of the instrument. If possible, the normally used 
transmitter, receiver, and, as appropriate, reflecting devices 
should be used during the audit, and the normal monitoring 
configuration of the instrument should be modified as little as 
possible to accommodate the test cell for the audit. However, if 
permitted by the associated operation or instruction manual, an 
alternate local light source or an alternate optical path that does 
not include the normal atmospheric monitoring path may be used. The 
actual concentrations of the audit gas in the test cell must be 
selected to produce ``effective concentrations'' in the ranges 
specified in this Sec. 3.2. Generally, each audit concentration 
measurement result will be the sum of the atmospheric pollutant 
concentration and the audit test concentration. If so, the result 
must be corrected to remove the atmospheric concentration 
contribution. The ``corrected concentration'' is obtained by 
subtracting the average of the atmospheric concentration measured by 
the instrument immediately before and immediately after the audit 
test (or preferably before and after each audit concentration level) 
from the audit concentration measurement. If the difference between 
the before and after measurements is greater than 20 percent of the 
effective concentration of the test gas standard, discard the test 
result for that concentration level and repeat the test for that 
level. If possible, open path analyzers should be audited during 
periods when the atmospheric pollutant concentrations are relatively 
low and steady.
    Report both the audit test concentrations (effective 
concentrations for open path analyzers) and the corresponding 
concentration measurements (corrected concentrations, if applicable, 
for open path analyzers) indicated or produced by the analyzer being 
tested. The percent differences between these concentrations are 
used to assess the accuracy of the monitoring data as described in 
Sec. 5.2.
* * * * *

                                Table A-1.--Minimum Data Assessment Requirements                                
----------------------------------------------------------------------------------------------------------------
       Method            Assessment method          Coverage           Minimum frequency     Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:                                                                                                      
    Automated Methods  Response check at      Each analyzer........  Once per 2 weeks.....  Actual              
     for SO2, NO2,      concentration                                                        concentration\2\   
     O3, and CO.        between .08 & .10                                                    and measured       
                        ppm (8 & 10 ppm for                                                  concentration.\3\  
                        CO)\2\.                                                                                 
    Manual methods     Collocated samplers..  1 site for 1-5 sites;  Once per week........  Two concentration   
     including lead.                           2 sites for 6-20                              measurements.      
                                               sites; 3 sites > 20                                              
                                               sites; (sites with                                               
                                               highest conc.).                                                  
Accuracy:                                                                                                       
    Automated Methods  Response check at:     1. Each analyzer. 2.   1. Once per year. 2.   Actual              
     for SO2, NO2,      .03-.08 ppm,12 .15-    25% of analyzers (at   Each calendar          concentration\2\   
     O3, and CO.        .20 ppm;12 .35-.45     least 1).              quarter.               and measured       
                        ppm;12 .80-.90                                                       (indicated)        
                        ppm;12 (if                                                           concentration\3\   
                        applicable).                                                         for each level.    
    Manual methods     Check of analytical    Analytical system....  Each day samples are   Actual concentration
     for SO2 and NO2.   procedures with                               analyzed, at least     and measured       
                        audit standard                                twice per quarter.     (indicated)        
                        solutions.                                                           concentration for  
                                                                                             each audit         
                                                                                             solution.          
    TSP, PM-10.......  Check of sampler flow  1. Each sampler. 2.    1. Once per year. 2.   Actual flow rate and
                        rate.                  25% of samplers (at    Each calendar          flow rate indicated
                                               least 1).              quarter.               by the sampler.    
    Lead.............  1. Check sample flow   1. Each sampler. 2.    1. Include with TSP.   1. Same as for TSP. 
                        rate as for TSP. 2.    Analytical system.     2. Each quarter.       2. Actual          
                        Check analytical                                                     concentration &    
                        system with Pb audit                                                 measured           
                        strips.                                                              (indicated)        
                                                                                             concentration of   
                                                                                             audit samples      
                                                                                             (g Pb/    
                                                                                             strip).            
----------------------------------------------------------------------------------------------------------------
\1\Concentration times 100 for CO.                                                                              
\2\Effective concentration for open path analyzers.                                                             
\3\Corrected concentration, if applicable, for open path analyzers.                                             

* * * * *

Appendix B [Amended]

    4. Appendix B is amended as follows:
    a. The first paragraph of section is revised.
    b. Section 3.1 is revised.
    c. The text preceding the table in the first paragraph, and the 
third, and fourth paragraphs of section 3.2 are revised; and a new 
paragraph is added between the third and fourth paragraphs.
    d. Table B-1 is revised.

Appendix B--Quality Assurance Requirements for Prevention of 
Significant Deterioration (PSD) Air Monitoring

* * * * *

3. Data Quality Assessment Requirements

    All ambient monitoring methods or analyzers used in PSD 
monitoring shall be tested periodically, as described in this 
section 3, to quantitatively assess the quality of the data being 
routinely collected. The results of these tests shall be reported as 
specified in section 6. Concentration standards used for the tests 
must be as specified in section Sec. 2.3. Additional information and 
guidance in the technical aspects of conducting these tests may be 
found in Reference 3 or in the operation or instruction manual 
associated with the analyzer or sampler. Concentration measurements 
reported from analyzers or analytical systems must be derived by 
means of the same calibration curve and data processing system used 
to obtain the routine air monitoring data. Table B-1 provides a 
summary of the minimum data quality assessment requirements, which 
are described in more detail in the following sections.

3.1  Precision of Automated Methods

    A one-point precision check must be carried out at least once 
every 2 weeks on each automated analyzer used to measure SO2, 
NO2, O3, and CO. The precision check is made by 
challenging the analyzer with a precision check gas of known 
concentration (effective concentration for open path analyzers) 
between 0.08 and 0.10 ppm for SO2, NO2, and O3 
analyzers, and between 8 and 10 ppm for CO analyzers. The standards 
from which precision check test concentrations are obtained must 
meet the specifications of section 2.3. Except for certain CO 
analyzers described below, point analyzers must operate in their 
normal sampling mode during the precision check, and the test 
atmosphere must pass through all filters, scrubbers, conditioners 
and other components used during normal ambient sampling and as much 
of the ambient air inlet system as is practicable. If permitted by 
the associated operation or instruction manual, a CO point analyzer 
may be temporarily modified during the precision check to reduce 
vent or purge flows, or the test atmosphere may enter the analyzer 
at a point other than the normal sample inlet, provided that the 
analyzer's response is not likely to be altered by these deviations 
from the normal operational mode.
    Open path analyzers are tested by inserting a test cell 
containing a precision check gas concentration into the optical 
measurement beam of the instrument. If possible, the normally used 
transmitter, receiver, and, as appropriate, reflecting devices 
should be used during the test, and the normal monitoring 
configuration of the instrument should be altered as little as 
possible to accommodate the test cell for the test. However, if 
permitted by the associated operation or instruction manual, an 
alternate local light source or an alternate optical path that does 
not include the normal atmospheric monitoring path may be used. The 
actual concentration of the precision check gas in the test cell 
must be selected to produce an ``effective concentration'' in the 
range specified above. Generally, the precision test concentration 
measurement will be the sum of the atmospheric pollutant 
concentration and the precision test concentration. If so, the 
result must be corrected to remove the atmospheric concentration 
contribution. The ``corrected concentration'' is obtained by 
subtracting the average of the atmospheric concentrations measured 
by the instrument immediately before and immediately after the 
precision check test from the precision test concentration 
measurement. If the difference between these before and after 
measurements is greater than 20 percent of the effective 
concentration of the test gas, discard the test result and repeat 
the test. If possible, open path analyzers should be tested during 
periods when the atmospheric pollutant concentrations are relatively 
low and steady.
    If a precision check is made in conjunction with a zero or span 
adjustment, it must be made prior to such zero or span adjustment. 
The difference between the actual concentration (effective 
concentration for open path analyzers) of the precision check gas 
and the corresponding concentration measurement (corrected 
concentration, if applicable, for open path analyzers) indicated by 
the analyzer is used to assess the precision of the monitoring data 
as described in 4.1. Report data only from automated analyzers that 
are approved for use in the PSD network.

3.2  Accuracy of Automated Methods

    Each sampling quarter audit each analyzer that monitors for 
SO2, NO2, O3, or CO at least once. The audit is made 
by challenging the analyzer with at least one audit gas of known 
concentration (effective concentration for open path analyzers) from 
each of the following ranges that fall within the measurement range 
of the analyzer being audited: * * *
    For point analyzers, the audit shall be carried out by allowing 
the analyzer to analyze the audit test atmosphere in the same manner 
as described for precision checks in Sec. 3.1. The exception given 
in Sec. 3.1 for certain CO analyzers does not apply for audits.
    Open path analyzers are audited by inserting a test cell 
containing an audit gas concentration into the optical measurement 
beam of the instrument. If possible, the normally used transmitter, 
receiver, and, as appropriate, reflecting devices should be used 
during the audit, and the normal monitoring configuration of the 
instrument should be modified as little as possible to accommodate 
the test cell for the audit. However, if permitted by the associated 
operation or instruction manual, an alternate local light source or 
an alternate optical path that does not include the normal 
atmospheric monitoring path may be used. The actual concentrations 
of the audit gas in the test cell must be selected to produce 
``effective concentrations'' in the range specified in this section 
3.2. Generally, each audit concentration measurement result will be 
the sum of the atmospheric pollutant concentration and the audit 
test concentration. If so, the result must be corrected to remove 
the atmospheric concentration contribution. The ``corrected 
concentration'' is obtained by subtracting the average of the 
atmospheric concentrations measured by the instrument immediately 
before and immediately after the audit test (or preferably before 
and after each audit concentration level) from the audit 
concentration measurement. If the difference between these before 
and after measurements is greater than 20 percent of the effective 
concentration of the test gas standards, discard the test result for 
that concentration level and repeat the test for that level. If 
possible, open path analyzers should be audited during periods when 
the atmospheric pollutant concentrations are relatively low and 
steady.
    The differences between the actual concentrations (effective 
concentrations for open path analyzers) of the audit test gas and 
the corresponding concentration measurements (corrected 
concentrations, if applicable, for open path analyzers) indicated by 
the analyzer are used to assess the accuracy of the monitoring data 
as described in Sec. 4.2. Report data only from automated analyzers 
that are approved for use in the PSD network.
* * * * *

                              Table B-1.--Minimum PSD Data Assessment Requirements                              
----------------------------------------------------------------------------------------------------------------
       Method            Assessment method          Coverage               Frequency         Parameters reported
----------------------------------------------------------------------------------------------------------------
Precision:                                                                                                      
    Automated Methods  Response check at      Each analyzer........  Once per 2 weeks.....  Actual              
     for SO2, NO2,      concentration                                                        concentration\2\   
     O3, and CO.        between .08 and .10                                                  and measured       
                        ppm (8 and 10 ppm                                                    concentration.\3\  
                        for CO)\2\.                                                                             
    TSP, PM10, Lead..  Collocated samplers..  Highest concentration  Once per week or       Two concentration   
                                               site in monitoring     every 3rd day for      measurements.      
                                               network.               continuous sampling.                      
Accuracy:                                                                                                       
    Automated Methods  Response check at:     Each analyzer........  Once per sampling      Actual              
     for SO2, NO2,      .03-.08 ppm;\1\\2\                            quarter.               concentration\2\   
     O3, and CO.        .15-.20 ppm;\1\\2\                                                   and measured       
                        .35-.45 ppm;\1\\2\                                                   (indicated)        
                        .80-.90 ppm;\1\\2\                                                   concentration\3\   
                        (if applicable).                                                     for each level.    
    TSP, PM10........  Sampler flow check...  Each sampler.........  Once per sampling      Actual flow rate and
                                                                      quarter.               flow rate indicated
                                                                                             by the sampler.    
    Lead.............  1. Sample flow rate    1. Each sampler. 2.    1. Once/quarter. 2.    1. Same as for TSP. 
                        check. 2. Check        Analytical system.     Each quarter Pb        2. Actual          
                        analytical system                             samples are analyzed.  concentration and  
                        with Pb audit strips.                                                measured           
                                                                                             concentration of   
                                                                                             audit samples      
                                                                                             (g Pb/    
                                                                                             strip).            
----------------------------------------------------------------------------------------------------------------
\1\Concentration shown times 100 for CO.                                                                        
\2\Effective concentration for open path analyzers.                                                             
\3\Corrected concentration, if applicable, for open path analyzers.                                             

* * * * *

Appendix E [Amended]

    5. Appendix E is amended as follows:
    a. The title of appendix E is revised.
    b. Section 1 is revised.
    c. Section 2 is added and sections 3, 5, and 6 are removed and 
reserved.
    d. Section 4 is revised.
    e. In section 7 table 3 is removed and table 4 is redesignated as 
table 3.
    f. The first paragraph of section 9 is revised.
    g. Section 10 is revised.
    h. Section 12 is revised.

Appendix E--Probe and Monitoring Path Siting Criteria for Ambient Air 
Quality Monitoring

1. Introduction

    This appendix contains specific location criteria applicable to 
ambient air quality monitoring probes and monitoring paths after the 
general station siting has been selected based on the monitoring 
objectives and spatial scale of representation discussed in Appendix 
D of this part. Adherence to these siting criteria is necessary to 
ensure the uniform collection of compatible and comparable air 
quality data.
    The probe and monitoring path siting criteria discussed below 
must be followed to the maximum extent possible. It is recognized 
that there may be situations where some deviation from the siting 
criteria may be necessary. In any such case, the reasons must be 
thoroughly documented in a written request for a waiver that 
describes how and why the proposed siting deviates from the 
criteria. This documentation should help to avoid later questions 
about the validity of the resulting monitoring data. Conditions 
under which EPA would consider an application for waiver from these 
siting criteria are discussed in section 11 of this appendix.
    The spatial scales of representation used in this appendix, 
i.e., micro, middle, neighborhood, urban, and regional, are defined 
and discussed in Appendix D of this part. The pollutant-specific 
probe and monitoring path siting criteria generally apply to all 
spatial scales except where noted otherwise. Specific siting 
criteria that are phrased with a ``must'' are defined as 
requirements and exceptions must be approved through the waiver 
provisions. However, siting criteria that are phrased with a 
``should'' are defined as goals to meet for consistency but are not 
requirements.
* * * * *

2. Sulfur Dioxide (SO2), Ozone (O3), and Nitrogen Dioxide 
(NO2)

    Additional information on SO2, NO2, and O3 
monitor siting criteria may be found in references 11 and 13.
    2.1  Horizontal and Vertical Placement. The probe or at least 80 
percent of the monitoring path must be located between 3 and 15 
meters above ground level. The probe or at least 90 percent of the 
monitoring path must be at least 1 meter vertically or horizontally 
away from any supporting structure, walls, parapets, penthouses, 
etc., and away from dusty or dirty areas. If the probe or a 
significant portion of the monitoring path is located near the side 
of a building, then it should be located on the windward side of the 
building relative to the prevailing wind direction during the season 
of highest concentration potential for the pollutant being measured.
    2.2  Spacing from Minor Sources (applicable to SO2 and 
O3 monitoring only). Local minor sources of SO2 can cause 
inappropriately high concentrations of SO2 in the vicinity of 
probes and monitoring paths for SO2. Similarly, local sources 
of nitric oxide (NO) and ozone-reactive hydrocarbons can have a 
scavenging effect causing unrepresentatively low concentrations of 
O3 in the vicinity of probes and monitoring paths for O3. 
To minimize these potential interferences, the probe or at least 90 
percent of the monitoring path must be away from furnace or 
incineration flues or other minor sources of SO2 or NO, 
particularly for open path analyzers because of their potential for 
greater exposure over the area covered by the monitoring path. The 
separation distance should take into account the height of the 
flues, type of waste or fuel burned, and the sulfur content of the 
fuel. It is acceptable, however, to monitor for SO2 near a 
point source of SO2 when the objective is to assess the effect 
of this source on the represented population.
    2.3  Spacing from Obstructions. Buildings and other obstacles 
may possibly scavenge SO2, O3, or NO2. To avoid this 
interference, the probe or at least 90 percent of the monitoring 
path must have unrestricted airflow and be located away from 
obstacles so that the distance from the probe or monitoring path is 
at least twice the height that the obstacle protrudes above the 
probe or monitoring path. Generally, a probe or monitoring path 
located near or along a vertical wall is undesirable because air 
moving along the wall may be subject to possible removal mechanisms. 
A probe must have unrestricted airflow in an arc of at least 270 
degrees around the inlet probe, or 180 degrees if the probe is on 
the side of a building. This arc must include the predominant wind 
direction for the season of greatest pollutant concentration 
potential. A sampling station having a probe located closer to an 
obstacle than this criterion allows should be classified as middle 
scale rather than neighborhood or urban scale, since the 
measurements from such a station would more closely represent the 
middle scale. A monitoring path must be clear of all trees, brush, 
buildings, plumes, dust, or other optical obstructions, including 
potential obstructions that may move due to wind, human activity, 
growth of vegetation, etc. Temporary optical obstructions, such as 
rain, particles, fog, or snow, should be considered when siting an 
open path analyzer. Any of these temporary obstructions that are of 
sufficient density to obscure the light beam will affect the ability 
of the open path analyzer to continuously measure pollutant 
concentrations.
    2.4  Spacing from Trees. Trees can provide surfaces for 
SO2, O3, or NO2 adsorption or reactions and obstruct 
wind flow. To reduce this possible interference, the probe or at 
least 90 percent of the monitoring path should be 20 meters or more 
from the drip line of trees. If a tree or trees could be considered 
an obstacle, the probe or 90 percent of the monitoring path must 
meet the distance requirements of 2.3 and be at least 10 meters from 
the drip line of the tree or trees. Since the scavenging effect of 
trees is greater for O3 than for other criteria pollutants, 
strong consideration of this effect must be given to locating an 
O3 probe or monitoring path to avoid this problem.
    2.5  Spacing from Roadways (applicable to O3 and NO2 
only). In siting an O3 analyzer, it is important to minimize 
destructive interferences from sources of NO, since NO readily 
reacts with O3. In siting NO2 analyzers for neighborhood 
and urban scale monitoring, it is important to minimize 
interferences from automotive sources. Table 1 provides the required 
minimum separation distances between a roadway and a probe and 
between a roadway and at least 90 percent of a monitoring path for 
various ranges of daily roadway traffic. A sampling station having a 
point analyzer probe located closer to a roadway than allowed by the 
Table 1 requirements should be classified as middle scale rather 
than neighborhood or urban scale, since the measurements from such a 
station would more closely represent the middle scale. The 
monitoring path of an open path analyzer must not cross over a 
roadway with an average daily traffic count of 10,000 vehicles per 
day or more. In calculating the percentage of a monitoring path over 
or near a roadway, one must consider the entire segment of the 
monitoring path in the area of potential atmospheric interference 
from automobile emissions. Therefore, this calculation must include 
the length of the monitoring path over the roadway plus any segments 
of the monitoring path that lie in the area between the roadway and 
the minimum separation distance, as determined from Table 1. The sum 
of these distances must not be greater than 10 percent of the total 
monitoring path length.

  Table 1.--Minimum Separation Distance Between Roadways and Probes or  
 Monitoring Paths for Monitoring Neighborhood--and Urban-Scale Ozone and
                            Nitrogen Dioxide                            
------------------------------------------------------------------------
                                                               Minimum  
                                                             separation 
      Roadway average daily traffic, vehicles per day       distance\1\,
                                                               meters   
------------------------------------------------------------------------
10,000.........................................           10 
15,000....................................................           20 
20,000....................................................           30 
40,000....................................................           50 
70,000....................................................          100 
110,000........................................          250 
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for 
  intermediate traffic counts should be interpolated from the table     
  values based on the actual traffic count.                             

    2.6  Cumulative Interferences on a Monitoring Path. The 
cumulative length or portion of a monitoring path that is affected 
by minor sources, obstructions, trees, or roadways must not exceed 
10 percent of the total monitoring path length.
    2.7  Maximum Monitoring Path Length. The monitoring path length 
must not exceed 1 kilometer for analyzers in neighborhood, urban, or 
regional scale. For middle scale monitoring sites, the monitoring 
path length must not exceed 300 meters. In areas subject to frequent 
periods of dust, fog, rain, or snow, consideration should be given 
to a shortened monitoring path length to minimize loss of monitoring 
data due to these temporary optical obstructions. For certain 
ambient air monitoring scenarios using open path analyzers, shorter 
path lengths may be needed in order to ensure that the monitoring 
station meets the objectives and spatial scales defined for SLAMS in 
Appendix D. Therefore, the Regional Administrator or the Regional 
Administrator's designee may require shorter path lengths, as needed 
on an individual basis, to ensure that the SLAMS meet the Appendix D 
requirements. Likewise, the Administrator or the Administrator's 
designee may specify the maximum path length used at monitoring 
stations designated as NAMS or PAMS as needed on an individual 
basis.
* * * * *

4. Carbon Monoxide (CO)

    Open path analyzers may be used to measure CO for only middle or 
neighborhood scale measurement applications if the open path 
analyzer is designated as a SLAMS. Additional information on CO 
monitor siting criteria may be found in reference 12.
    4.1  Horizontal and Vertical Placement. Because of the 
importance of measuring population exposure to CO concentrations, 
air should be sampled at average breathing heights. However, 
practical factors require that the inlet probe be higher. The 
required height of the inlet probe for CO monitoring is therefore 
3\1/2\ meter for a microscale site, which is a 
compromise between representative breathing height and prevention of 
vandalism. The recommended 1 meter range of heights is also a 
compromise to some extent. For consistency and comparability, it 
would be desirable to have all inlets at exactly the same height, 
but practical considerations often prevent this. Some reasonable 
range must be specified and 1 meter provides adequate leeway to meet 
most requirements.
    For the middle and neighborhood scale stations, the vertical 
concentration gradients are not as great as for the microscale 
station. This is because the diffusion from roads is greater and the 
concentrations would represent larger areas than for the microscale. 
Therefore, the probe or at least 80 percent of the monitoring path 
must be located between 3 and 15 meters above ground level for 
middle and neighborhood scale stations. The probe or at least 90 
percent of the monitoring path must be at least 1 meter vertically 
or horizontally away from any supporting structure, walls, parapets, 
penthouses, etc., and away from dusty or dirty areas. If the probe 
or a significant portion of the monitoring path is located near the 
side of a building, then it should be located on the windward side 
of the building relative to both the prevailing wind direction 
during the season of highest concentration potential and the 
location of sources of interest, i.e., roadways.
    4.2  Spacing from Obstructions. Buildings and other obstacles 
may restrict airflow around a probe or monitoring path. To avoid 
this interference, the probe or at least 90 percent of the 
monitoring path must have unrestricted airflow and be located away 
from obstacles so that the distance from the probe or monitoring 
path is at least twice the height that the obstacle protrudes above 
the probe or monitoring path. A probe or monitoring path located 
near or along a vertical wall is undesirable because air moving 
along the wall may be subject to possible removal mechanisms. A 
probe must have unrestricted airflow in an arc of at least 270 
degrees around the inlet probe, or 180 degrees if the probe is on 
the side of a building. This arc must include the predominant wind 
direction for the season of greatest pollutant concentration 
potential. A monitoring path must be clear of all trees, brush, 
buildings, plumes, dust, or other optical obstructions, including 
potential obstructions that may move due to wind, human activity, 
growth of vegetation, etc. Temporary optical obstructions, such as 
rain, particles, fog, or snow, should be considered when siting an 
open path analyzer. Any of these temporary obstructions that are of 
sufficient density to obscure the light beam will affect the ability 
of the open path analyzer to continuously measure pollutant 
concentrations.
    4.3  Spacing from Roadways. Street canyon and traffic corridor 
stations (microscale) are intended to provide a measurement of the 
influence of the immediate source on the pollution exposure of the 
population. In order to provide some reasonable consistency and 
comparability in the air quality data from microscale stations, a 
minimum distance of 2 meters and a maximum distance of 10 meters 
from the edge of the nearest traffic lane must be maintained for 
these CO monitoring inlet probes. This should give consistency to 
the data, yet still allow flexibility of finding suitable locations.
    Street canyon/corridor (microscale) inlet probes must be located 
at least 10 meters from an intersection and preferably at a midblock 
location. Midblock locations are preferable to intersection 
locations because intersections represent a much smaller portion of 
downtown space than do the streets between them. Pedestrian exposure 
is probably also greater in street canyon/corridors than at 
intersections. Also, the practical difficulty of positioning 
sampling inlets is less at midblock locations than at the 
intersection. However, the final siting of the monitor must meet the 
objectives and intent of appendix D, sections 2.4, 3, 3.3, and 
appendix E, section 4.
    In determining the minimum separation between a neighborhood 
scale monitoring station and a specific line source, the presumption 
is made that measurements should not be unduly influenced by any one 
roadway. Computations were made to determine the separation 
distance, and table 2 provides the required minimum separation 
distance between roadways and a probe or 90 percent of a monitoring 
path. Probes or monitoring paths that are located closer to roads 
than this criterion allows should not be classified as a 
neighborhood scale, since the measurements from such a station would 
closely represent the middle scale. Therefore, stations not meeting 
this criterion should be classified as middle scale. 

  Table 2.--Minimum Separation Distance Between Roadways and Probes or  
   Monitoring Paths for Monitoring Neighborhood Scale Carbon Monoxide   
------------------------------------------------------------------------
                                                               Minimum  
                                                              separation
                                                             distance\1\
                                                              for probes
      Roadway average daily traffic, vehicles per day        or 90% of a
                                                              monitoring
                                                                path,   
                                                               meters   
------------------------------------------------------------------------
10,000..........................................          10 
15,000.....................................................          25 
20,000.....................................................          45 
30,000.....................................................          80 
40,000.....................................................         115 
50,000.....................................................         135 
60,000..........................................         150 
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for 
  intermediate traffic counts should be interpolated from the table     
  values based on the actual traffic count.                             

    4.4 Spacing from Trees and Other Considerations. Since CO is 
relatively nonreactive, the major factor concerning trees is as 
obstructions to normal wind flow patterns. For middle and 
neighborhood scale stations, trees should not be located between the 
major sources of CO, usually vehicles on a heavily traveled road, 
and the monitor. The probe or at least 90 percent of the monitoring 
path must be 10 meters or more from the drip line of trees which are 
between the probe or monitoring path and the road and which extend 
at least 5 meters above the probe or monitoring path. For microscale 
stations, no trees or shrubs should be located between the probe and 
the roadway.
    4.5  Cumulative Interferences on a Monitoring Path. The 
cumulative length or portion of a monitoring path that is affected 
by obstructions, trees, or roadways must not exceed 10 percent of 
the total monitoring path length.
    4.6  Maximum Monitoring Path Length. The monitoring path length 
must not exceed 1 kilometer for analyzers used for neighborhood 
scale monitoring applications, or 300 meters for middle scale 
monitoring applications. In areas subject to frequent periods of 
dust, fog, rain, or snow, consideration should be given to a 
shortened monitoring path length to minimize loss of monitoring data 
due to these temporary optical obstructions. For certain ambient air 
monitoring scenarios using open path analyzers, shorter path lengths 
may be needed in order to ensure that the monitoring station meets 
the objectives and spatial scales defined for SLAMS in Appendix D. 
Therefore, the Regional Administrator or the Regional 
Administrator's designee may require shorter path lengths, as needed 
on an individual basis, to ensure that the SLAMS meet the Appendix D 
requirements. Likewise, the Administrator or the Administrator's 
designee may specify the maximum path length used at monitoring 
stations designated as NAMS or PAMS as needed on an individual 
basis.
* * * * *

9. Probe Material and Pollutant Sample Residence Time

    For the reactive gases, SO2, NO2, and O3, special 
probe material must be used for point analyzers. Studies20-24 
have been conducted to determine the suitability of materials such 
as polypropylene, polyethylene, polyvinylchloride, Tygon, aluminum, 
brass, stainless steel, copper, pyrex glass and teflon for use as 
intake sampling lines. Of the above materials, only pyrex glass and 
teflon have been found to be acceptable for use as intake sampling 
lines for all the reactive gaseous pollutants. Furthermore, EPA\25\ 
has specified borosilicate glass or FEP teflon as the only 
acceptable probe materials for delivering test atmospheres in the 
determination of reference or equivalent methods. Therefore, 
borosilicate glass, FEP teflon, or their equivalent must be used for 
existing and new NAMS or SLAMS.
* * * * *

10. Photochemical Assessment Monitoring Stations (PAMS)

    10.1  Horizontal and Vertical Placement. The probe or at least 
80 percent of the monitoring path must be located 3 to 15 meters 
above ground level. This range provides a practical compromise for 
finding suitable sites for the multi-pollutant PAMS. The probe or at 
least 90 percent of the monitoring path must be at least 1 meter 
vertically or horizontally away from any supporting structure, 
walls, parapets, penthouses, etc., and away from dusty or dirty 
areas.
    10.2  Spacing from Obstructions. The probe or at least 90 
percent of the monitoring path must be located away from obstacles 
and buildings such that the distance between the obstacles and the 
probe or monitoring path is at least twice the height that the 
obstacle protrudes above the probe or monitoring path. There must be 
unrestricted airflow in an arc of at least 270 deg. around the probe 
inlet. Additionally, the predominant wind direction for the period 
of greatest pollutant concentration (as described for each site in 
section 4.2 of Appendix D) must be included in the 270 deg. arc. If 
the probe is located on the side of the building, 180 deg. clearance 
is required. A monitoring path must be clear of all trees, brush, 
buildings, plumes, dust, or other optical obstructions, including 
potential obstructions that may move due to wind, human activity, 
growth of vegetation, etc. Temporary optical obstructions, such as 
rain, particles, fog, or snow, should be considered when siting an 
open path analyzer. Any of these temporary obstructions that are of 
sufficient density to obscure the light beam will affect the ability 
of the open path analyzer to continuously measure pollutant 
concentrations.
    10.3  Spacing from Roadways. It is important in the probe and 
monitoring path siting process to minimize destructive interferences 
from sources of NO since NO readily reacts with O3. Table 4 
below provides the required minimum separation distances between 
roadways and PAMS (excluding upper air measuring stations):

         Table 4.--Separation Distance Between PAMS and Roadways        
                     [Edge of Nearest Traffic Lane]                     
------------------------------------------------------------------------
                                                                Minimum 
                                                              separation
                                                               distance 
                                                                between 
      Roadway average daily traffic, vehicles per day          roadways 
                                                                  and   
                                                               stations 
                                                                  in    
                                                               meters\1\
------------------------------------------------------------------------
<10,000.....................................................         >10
15,000......................................................          20
20,000......................................................          30
40,000......................................................          50
70,000......................................................         100
>110,000....................................................        250 
------------------------------------------------------------------------
\1\Distance from the edge of the nearest traffic lane. The distance for 
  intermediate traffic counts should be interpolated from the table     
  based on the actual traffic flow.                                     

    10.4  Spacing from Trees. Trees can provide surfaces for 
adsorption and/or reactions to occur and can obstruct normal wind 
flow patterns. To minimize these effects at PAMS, the probe or at 
least 90 percent of the monitoring path should be placed at least 20 
meters from the drip line of trees. Since the scavenging effect of 
trees is greater for O3 than for the other criteria pollutants, 
strong consideration of this effect must be given in locating the 
PAMS probe or monitoring path to avoid this problem. Therefore, the 
probe or at least 90 percent of the monitoring path must be at least 
10 meters from the drip line of trees that are located between the 
urban city core area and the probe or monitoring path along the 
appropriate wind direction.
* * * * *

12. Summary

    Table 5 presents a summary of the general requirements for probe 
and monitoring path siting criteria with respect to distances and 
heights. It is apparent from Table 5 that different elevation 
distances above the ground are shown for the various pollutants. The 
discussion in the text for each of the pollutants described reasons 
for elevating the monitor, probe, or monitoring path. The 
differences in the specified range of heights are based on the 
vertical concentration gradients. For CO, the gradients in the 
vertical direction are very large for the microscale, so a small 
range of heights has been used. The upper limit of 15 meters was 
specified for consistency between pollutants and to allow the use of 
a single manifold or monitoring path for monitoring more than one 
pollutant.

                                             Table 5.--Summary of Probe and Monitoring Path Siting Criteria                                             
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                  Horizontal and                                                        
                                                       Height from ground to  vertical distance from                                                    
                          Scale [maximum monitoring       probe or 80% of     supporting structuresB    Distance from trees to    Distance from roadways
       Pollutant            path length, meters]         monitoring pathA       to probe or 90% of    probe or 90% of monitoring  to probe or monitoring
                                                             (meters)            monitoring pathA           pathA (meters)            pathA (meters)    
                                                                                     (meters)                                                           
--------------------------------------------------------------------------------------------------------------------------------------------------------
SO2 CDEF...............  Middle [300m] Neighborhood,  3-15..................  >1....................  >10.......................  N/A.                  
                          Urban, and Regional [1km].                                                                                                    
CO DEG.................  Micro, Middle [300m],        30.5, 3-15  >1....................  >10.......................  2-10, See Table 1 for 
                          Neighborhood [1km].                                                                                      middle and           
                                                                                                                                   neighborhood scales. 
O3CDE..................  Middle [300m],               3-15..................  >1....................  >10.......................  See Table 2 for all   
                          Neighborhood, Urban, and                                                                                 scales.              
                          Regional [1km].                                                                                                               
Ozone precursors (for    Neighborhood and Urban [1    3-15..................  >1....................  >10.......................  See Table 4 for all   
 PAMS)CDE.                km].                                                                                                     scales.              
NO2CDE.................  Middle [300m], Neighborhood  3-15..................  >1....................  >10.......................  See Table 2 for all   
                          and Urban [1km].                                                                                         scales.              
PbCDEFH................  Micro; Middle,               2-7 (Micro), 2-15 (All  >2 (All scales,         >10 (All scales)..........  5-15 (Micro), See     
                          Neighborhood, Urban and      other scales).          horizontal distance                                 Table 3 for all other
                          Regional.                                            only).                                              scales.              
PM-10CDEFH.............  Micro; Middle,               2-7 (Micro), 2-15 (All  >2 (All scales,         >10 (All scales)..........  2-10 (Micro), See     
                          Neighborhood, Urban and      other scales).          horizontal distance                                 Figure 2 for all     
                          Regional.                                            only).                                              other scales.        
--------------------------------------------------------------------------------------------------------------------------------------------------------
A Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring and all applicable scales for monitoring SO2,
  O3, O3 precursors, and NO2.                                                                                                                           
B When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.                       
N/A--Not applicable.                                                                                                                                    
C Should be >20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act as an obstruction.                     
D Distance from sampler, probe, or 90% of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes     
  above the sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text).                          
E Must have unrestricted airflow 270 deg. around the probe or sampler; 180 deg. if the probe is on the side of a building.                              
F The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is dependent 
  on the height of the minor source's emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur, ash, or   
  lead content). This criterion is designed to avoid undue influences from minor sources.                                                               
G For microscale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at a midblock location.                    
H For collocated Pb and PM-10 samplers, a 2-4 meter separation distance between collocated samplers must be met.                                        

* * * * *
[FR Doc. 94-20042 Filed 8-17-94; 8:45 am]
BILLING CODE 6560-50-P