[Federal Register Volume 88, Number 196 (Thursday, October 12, 2023)]
[Rules and Regulations]
[Pages 70595-70602]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-22531]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 50
[EPA-HQ-OAR-2022-0007; FRL-9344-02-OAR]
RIN 2060-AV63
Reference Measurement Principle and Calibration Procedure for the
Measurement of Ozone in the Atmosphere (Chemiluminescence Method)
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: The Environmental Protection Agency (EPA) is finalizing an
update to the current ozone absorption cross-section to the recommended
consensus-based cross-section value of 1.1329x10-17 cm\2\
molecule-1 or 304.39 atm-1 cm-1, with
an uncertainty of 0.94 atm-1 cm-1. The new value
is 1.2% lower than the current value of 308 atm-1
cm-1 and reduces the uncertainty in the value to 0.31%. The
adoption of this updated ozone absorption cross-section could result in
increases in measured ozone concentrations but given the existing
sources of potential variability in monitoring data, it is unlikely
that there will be any consistent measurable and predictable effect on
reported data. The EPA is also updating the dates of publication for
two references associated with the updated cross-section value, adding
a new reference, and making a technical correction to move three
figures inadvertently placed in section 6.0 References to a new section
7.0 Figures.
DATES: This final rule is effective on November 13, 2023.
ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2022-0007. All documents in the docket are
listed on the https://www.regulations.gov website. Although listed in
the index, some information is not publicly available, e.g., CBI or
other information whose disclosure is restricted by statute. Certain
other material, such as copyrighted material, is not placed on the
internet and will be publicly available only in hard copy form.
Publicly available docket materials are available electronically
through https://www.regulations.gov.
FOR FURTHER INFORMATION CONTACT: Ms. Joann Rice, Office of Air Quality
Planning and Standards, Air Quality Assessment Division, Ambient Air
Monitoring Group (C304-06), Environmental Protection Agency, Research
Triangle Park, North Carolina 27711; telephone number: (919) 541-3372;
email address: [email protected].
SUPPLEMENTARY INFORMATION:
Organization of this document. The information in this preamble is
organized as follows:
Table of Contents
I. Background
Comments on the Proposed Rule
II. Statutory and Executive Orders Reviews
A. Executive Order 12866: Regulatory Planning and Review and
Executive Order 14094: Modernizing Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132: Federalism
F. Executive Order 13175: Consultation and Coordination With
Indian Tribal Governments
G. Executive Order 13045: Protection of Children From
Environmental Health Risks and Safety Risks
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
I. National Technology Transfer and Advancement Act (NTTAA)
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
K. Congressional Review Act (CRA)
I. Background
In 1961, the ozone absorption cross-section was measured to be
1.1476 x10-17 cm\2\ molecule-1 or 308.3
atmosphere (atm)-1 centimeter (cm)-1 with a
reported relative standard uncertainty of 1.4% (Hearn, 1961).\1\ In the
1980s, the National Institute of Standards and Technology (NIST), in
collaboration with the EPA, developed the Standard Reference Photometer
(SRP), which is the international standard for the measurement of
ozone. The SRP is based on ultraviolet (UV) photometry and uses this
cross-section value as the reference value for UV ozone measurements.
To establish and maintain traceability, the readings of an ozone
analyzer are compared to a NIST-made ozone SRP through a hierarchy of
standards. Efforts to improve the accuracy of the ozone absorption
cross-section have continued over several years during which rigorous
assessment of the bias and uncertainty in the value became a high
priority.
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\1\ Hearn A.G. (1961). Absorption of ozone in ultra-violet and
visible regions of spectrum, Proc. Phys. Soc. 78 932, DOI: 10.1088/
0370-1328/78/5/340.
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The Gas Analysis Working Group of the Consultive Committee for
Metrology in Chemistry and Biology (CCQM-GAWG) of the Bureau of Weights
and Measures in France (BIPM) convened a task group in 2016 to review
all published measurements of the ozone cross-section since 1950. This
task group was also charged with recommending a consensus-based cross-
section value and associated uncertainty for adoption in measurements
of ozone concentrations by standard UV photometric instruments,
including the SRP. (Hodges et al., 2019).\2\
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\2\ Hodges, J.T., Viallon, J., Brewer, P.J., Drouin, B.J.,
Gorshelev, V., Janssen, C., Lee, S., Possolo, A., Smith, M.A.H.,
Walden, and Wielgosz, R.I. (2019). Recommendation of a consensus
value of the ozone absorption cross-section at 253.65 nm based on a
literature review, Metrologia, 56, 034001. https://doi.org/10.1088/1681-7575/ab0bdd.
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After publication in Hodges et al., 2019, the CCQM-GAWG \3\
convened an international group of stakeholders in October 2020 to
discuss adopting and implementing a globally coordinated change in the
cross-section value for surface ozone monitoring. This group,
representing several international and national metrology institutes,
NIST, and environmental agencies including EPA, agreed to adopt and
implement the new cross-section value as it represents a more accurate
value with less
[[Page 70596]]
uncertainty and is an advancement and improvement in the UV photometer
measurement method.
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\3\ https://www.bipm.org/en/committees/cc/ccqm/wg/ccqm-gawg-ozone-tg.
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40 CFR part 50, appendix D, ``Reference Measurement Principle and
Calibration Procedure for the Measurement of Ozone in the Atmosphere,''
currently provides EPA's ozone calibration procedure with a stated
value of 308 4 atm-1 cm-1. This
final action updates the ozone absorption cross-section to align with
the BIPM CCQM-GAWG's updated international cross-section value of
304.39 atm-1 cm-1 with an uncertainty of 0.94
atm-1 cm-1 at standard temperature and pressure
of 0 [deg]C and 1 atmosphere. The EPA agrees that the new cross-section
value results in an improvement in the accuracy of surface ozone
monitoring measurements by reducing uncertainty and is finalizing the
change in appendix D of part 50 to this more accurate consensus value.
The updated value reduces the uncertainty to 0.31% from the current
1.4%. The value is also 1.2% lower than the current value of 308
atmosphere atm-1 cm-1, a change that could result
in increases in measured ozone concentrations. However, there are
several factors that EPA believes make it unlikely that this change
will have a measurable, predictable influence on any particular set of
ozone monitoring data.
Design values, the metric used to compare ambient ozone
concentrations measured at a monitor to the National Ambient Air
Quality Standard (NAAQS) to determine compliance, are determined using
the data reporting, data handling, and computation procedures provided
in 40 CFR part 50, appendix U, ``Interpretation of the Primary and
Secondary National Ambient Air Quality Standards for Ozone.''
Multiple factors can contribute to variability in monitoring data
and ultimately design values, including, but not limited to, the
precision of the monitoring method, the acceptance criteria for
Standard Reference Photometer (SRP) calibration and verification, the
acceptance criterion for bench and field standards used to calibrate
ozone monitors in the field, how agencies perform calibration and
adjust analyzer response, the precision and bias acceptance criteria in
EPA's Quality Assurance (QA) Handbook,\4\ data handling and computation
procedures in Appendix U, and meteorology.
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\4\ Quality Assurance Handbook for Air Pollution Measurement
Systems, Volume II, EPA-454/B-17-001, Jan. 2017, available at:
https://www.epa.gov/sites/default/files/2020-10/documents/final_handbook_document_1_17.pdf.
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The inherent precision (variability) of the measurements from
analyzers used to measure ozone is about 1 ppb, or 0.001 ppm. The variability in the measurement in either the
positive or negative direction should be considered relative to the
change in monitoring data due to the new cross-section value.
When the new cross-section value is implemented, all SRPs
maintained by BIPM, NIST, and the EPA will be updated to incorporate
the new value. The update will be achieved through software/firmware
modification and will not require any hardware changes. The EPA is
planning to update all Agency's SRPs simultaneously, instead of through
a phased approach, to minimize disruption of the SRP network. To
establish and maintain traceability, the readings of an ozone analyzer
are compared through a hierarchy of standards to a NIST ozone SRP. The
process of using NIST-traceable standards to verify the ozone
concentrations is implemented for all regulatory network ozone
analyzers used for comparison to the NAAQS. There are 12 SRPs within
the EPA's network: three at EPA's Office of Research and Development
(ORD) and nine at various EPA Regional offices and the California Air
Resources Board (CARB). One of ORD's SRPs is sent to NIST to be re-
verified against the NIST SRP annually. That SRP serves as the
reference for the two other ORD SRPs. Each SRP in the U.S. is re-
verified against one of ORD's three SRPs annually. Under normal
verification operations, implementing the ozone standards traceability
process for the entire SRP network could take 2 or more years starting
from when the SRP software/firmware is updated. During this time, the
implementation progress and monitoring data collected with the new
cross-section will need to be tracked.
The acceptance criteria used in comparing the SRPs (Level 1
standards) to each other is a slope of 1.00 0.01 (or 1%)
and an intercept 0.00 1 ppb. Field and bench standards
(Level 2 standard) used to calibrate ozone analyzers in the field have
acceptance criteria for the slope of 1.00 0.03 (or 3%) and
an intercept of 0 3 ppb. The 1.2% change in cross-section
value is well within the 3% acceptance for Level 2 standards.
The goal for annual measurement uncertainty for ozone in 40 CFR
part 58, ``Ambient Air Quality Surveillance,'' is an upper 90 percent
confidence limit for the coefficient of variation of 7% for precision
and for bias an upper 95 percent confidence limit of 7%. Bias and
precision estimates are determined using data obtained from the
comparison of the ozone analyzer response to one-point Quality Control
(QC) checks using a Level 2 calibration standard. The 1.2% change in
cross-section value is well within the bias and precision goal of 7%.
Data reported to the EPA's Air Quality System by state, local, and
tribal monitoring agencies is used to assess bias and precision. The
2021 national average precision for all ozone analyzers in the U.S. is
2.3% and the national average bias is 1.6%.\5\ The 1.2% change is,
therefore, within the national precision and less than the national
bias.
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\5\ Data obtained on 9/1/2022 from EPA's Ozone Data Quality
Dashboard: https://sti-r-shiny.shinyapps.io/ozone_dashboard/.
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The QA Handbook, Volume II, Appendix D Validation Template \6\ also
specifies critical criteria for monitoring organizations to maintain
the integrity and evaluate the quality of the data collected by the
analyzer. The critical criteria are a one-point QC check (every 14 days
at a minimum) < 7.1% difference or < 1.5 ppb
difference, whichever is greater; zero drift < 3.1 ppb
(over a 24-hour period) or < 5.1 ppb (>24 hours and up to
14 days); and span check drift over a 14-day period of < 7.1%. Any change to monitoring data due to the new cross-section
is also well within the 7.1% acceptance criteria. Monitoring
organizations may manually adjust the analyzer response while others
may institute automated adjustment through use of a data acquisition or
data handling system. Automated adjustments to the ozone analyzer data
are not recommended because the monitoring agency may not know if the
standard being used for monitor comparison, or the analyzer, has
degraded or drifted.
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\6\ Appendix D, Measurement Quality Objectives and Validation
Templates: https://www.epa.gov/sites/default/files/2020-10/documents/app_d_validation_template_version_03_2017_for_amtic_rev_1.pdf.
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Ozone analyzers are calibrated or verified every 182 days if one-
point zero and span checks are performed every 14 days, and every 365
days if one-point zero and span checks are done daily. The acceptance
criteria for multi-point calibration are all points < 2.1%
or <= 1.5 ppb difference of the best fit straight line,
whichever is greater, and a slope of 1 0.05 or 5%. The
1.2% change is also well within this acceptance criteria for ozone
monitor calibration.
Ozone design values are computed as the 3-year average of the
annual 4th highest daily maximum 8-hour value
[[Page 70597]]
measured at each monitoring site. Appendix U provides for three levels
of truncation for the hourly, daily 8-hour maximum, and design value
calculations. Hourly averaged ozone monitoring data are to be reported
in ppm to the third decimal place, with additional digits to the right
truncated (e.g., 0.070 ppm). In assessing how and if the updated cross-
section value may affect ozone design values, it is important to note
that other factors, including meteorology, can also influence design
values. The effects of meteorology on hourly ozone concentrations can
contribute to an increase or decrease in design values for a site
because formation of ozone is heavily dependent on meteorological
conditions. Interannual meteorological variations are known to affect
daily and seasonal average ozone concentrations. Therefore, while we do
not have reason to believe this proposal will significantly increase
design values, meteorology would be a confounding factor in determining
the effect on 3-year design values.
Taking these factors into consideration, the EPA believes it is
unlikely that the cross-section change will have a measurable,
predictable influence on any given ozone design value or monitoring
data set.
Because the EPA believes that adoption of the new cross-section
will improve the accuracy of measured ozone values and is unlikely to
have a measurable, predictable influence on any given monitor or design
value, the EPA is finalizing its proposal to revise the current ozone
absorption cross-section to the recommended international consensus-
based cross-section value of 304.39 atm-1 cm-1,
with an uncertainty of 0.94 atm-1 cm-1.
Ozone analyzers are traceable to a NIST standard reference UV-based
photometer with a specified ozone UV absorption cross-section value.
The absorption cross-section value stated this appendix (304.39
atm-1 cm-1 0.94 atm-1
cm-1) will be implemented January 1, 2025, with an
additional year for state, local, and tribal monitoring agencies to
complete implementation, to January 1, 2026. Until January 1, 2025, the
previous ozone absorption cross-section value (308 4
atm-1 cm-1) will be used. After January 1, 2025,
both cross-section values, 304.39 0.94 atm-1
cm-1 and 308 4 atm-1
cm-1, may be used. After January 1, 2026, only the cross-
section value of 304.39 0.94 atm-1
cm-1 may be used. EPA recognizes the challenges, complexity,
and time it will take to develop guidance and complete implementation
of the updated cross-section value and is, therefore, delaying the
proposed implementation start date of January 1, 2024, until January 1,
2025, with an additional year (to January 1, 2026) to complete
implementation.
The EPA is including an additional published reference for the
research done to support the cross-section change in 40 CFR part 50,
appendix D, section 6.0 References: Hodges, J.T., Viallon, J., Brewer,
P.J., Drouin, B.J., Gorshelev, V., Janssen, C., Lee, S., Possolo, A.,
Smith, M.A.H., Walden, and Wielgosz, R.I., ``Recommendation of a
consensus value of the ozone absorption cross-section at 253.65 nm
based on a literature review,'' Metrologia, 56 (2019) 034001, https://doi.org/10.1088/1681-7575/ab0bdd. The EPA is also changing the
publication dates of two existing references associated with the
updated cross-section value in 40 CFR part 50, appendix D, section 6.0
References.
Comments on the Proposed Rule
On February 24, 2023, the EPA proposed to update the current ozone
absorption cross-section (88 FR 11835) and solicited comment on the
proposed update. The EPA received two comments by the close of the
public comment period on March 27, 2023. One commenter expressed
concern that the proposed target date of January 1, 2024, provides
insufficient time to implement the new cross-section value and noted
that monitoring equipment that is no longer supported by manufacturers
would require monitoring agencies to purchase new ozone monitoring
equipment.
In further consideration of global implementation of the updated
cross-section value, the international task group leading
implementation and the EPA recognize the challenges, complexity, and
time it will take to implement the updated value and are accordingly
delaying the implementation start date from January 2024 until January
2025 with an additional year (to January 2026) to complete
implementation. Regarding the assertion that some monitoring agencies
will be required to purchase new equipment, existing equipment will be
adjusted by firmware updates if available. Where firmware updates are
not available for certain monitors, those monitors may instead be
calibrated against ozone transfer standards, which are calibrated
directly back to a Standard Reference Photometer (SRP) using the
updated cross-section value. Therefore, the purchase of new equipment
should not be required.
A second comment on the proposed cross-section value assumed that
the percentage increase in monitoring data would be 0.00086 ppm at the
current level of the standard (0.070 ppm). The commenter noted that, if
that increase had been applied to the health studies upon which the
current NAAQS is based, ``a NAAQS closer to 71 ppb very well could have
been chosen based on the monitoring data.'' The commenter also noted
that under the current ozone reconsideration, the Clean Air Science
Advisory Committee (CASAC) and EPA ``must'' consider the ozone cross-
section change on monitoring data and health effect studies and, if not
considered, the NAAQS may be ``artificially lowered'' or more
stringent.
The EPA disagrees that this change will make the NAAQS ozone
standard more stringent. As described in the proposed action, at the
current level of the standard (0.070 ppm), 0.00086 ppm is within the
current precision of the measurement method which is +/- 0.001 ppm.
Moreover, when viewed in conjunction with the current monitor
calibration acceptance criteria \7\, the use of truncation conventions
for the ozone hourly, daily 8-hour maximum, and design value
calculations, and other unpredictable factors, EPA disagrees with the
commenter's suggestion that the change will result in any consistent
measurable and predictable effect on reported data. This inherent
measurement variability is already included in the measurements that
have been and are being used in health effects research studies related
to the ozone NAAQS. The CASAC is aware of this action, which is
required to bring the U.S. into alignment with international monitoring
standards.
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\7\ See QA Handbook, Vol. II, App. D, Measurement Quality
Objectives and Validation Templates, available at https://www.epa.gov/sites/default/files/2020-10/documents/app_d_validation_template_version_03_2017_for_amtic_rev_1.pdf.
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No other comments were received. The EPA is finalizing this action
as proposed.
II. Statutory and Executive Orders Reviews
Additional information about these statutes and Executive Orders
can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 14094: Modernizing Regulatory Review
This action is not a significant regulatory action as defined by
Executive Order 12866, as amended by
[[Page 70598]]
Executive Order 14094 and was, therefore, not subject to a requirement
for Executive Order 12866 review.
B. Paperwork Reduction Act (PRA)
This action does not impose an information collection burden under
the PRA. This action revises the ozone absorption cross-section and
revise and amend relevant references. It does not contain any
information collection activities.
C. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. In
making this determination, the EPA concludes that the impact of concern
for this rule is any significant adverse economic impact on small
entities and that the agency is certifying that this rule will not have
a significant economic impact on a substantial number of small entities
if the rule has no net burden on the small entities subject to the
rule. This action updates the ozone absorption cross-section value for
surface ozone monitoring under 40 CFR part 50, and we anticipate that
there will be minimal costs associated with this change. We have,
therefore, concluded that this action will have no net regulatory
burden for all directly regulated small entities.
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538 and does not significantly or uniquely affect
small governments. This action imposes no enforceable duty on any
state, local, or tribal governments, or the private sector.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have tribal implications as specified in
Executive Order 13175. This action updates a reference measurement
principle and calibration procedure for the measurement of ambient
ozone under 40 CFR part 50. Thus, Executive Order 13175 does not apply
to this action.
G. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
The EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that the EPA has reason to believe may disproportionately affect
children, per the definition of ``covered regulatory action'' in
section 2-202 of the Executive Order. This action is not subject to
Executive Order 13045 because it does not concern an environmental
health risk or safety risk.
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
This action is not subject to Executive Order 13211, because it is
not a significant regulatory action under Executive Order 12866.
I. National Technology Transfer and Advancement Act (NTTAA)
This rulemaking involves technical standards. The EPA used
voluntary consensus standards in the preparation of this measurement
principle and procedure; it is the benchmark against which all ambient
ozone monitoring methods are compared. This action is simply updating
the reference measurement principle in light of updated information.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
Executive Order 12898 (59 FR 7629, Feb.16, 1994) directs Federal
agencies, to the greatest extent practicable and permitted by law, to
make environmental justice part of their mission by identifying and
addressing, as appropriate, disproportionately high and adverse human
health or environmental effects of their programs, policies, and
activities on minority populations (people of color) and low-income
populations.
The EPA believes that this type of action does not concern human
health or environmental conditions and, therefore, cannot be evaluated
with respect to potentially disproportionate and adverse effects on
people of color, low-income populations and/or indigenous peoples. This
regulatory action is an update to a previously promulgated analytical
method and does not have any impact on human health or the environment.
K. Congressional Review Act (CRA)
This action is subject to the CRA, and the EPA will submit a rule
report to each house of the Congress and to the Comptroller General of
the United States. This action is not a ``major rule'' as defined by 5
U.S.C. 804(2).
List of Subjects in 40 CFR Part 50
Environmental protection, Air pollution control, Ozone.
Michael S. Regan,
Administrator.
For the reasons set forth in the preamble, the EPA amends title 40,
chapter I of the Code of Federal Regulations as follows:
PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY
STANDARDS
0
1. The authority citation for part 50 continues to read as follows:
Authority: 42 U.S.C. 7401, et seq.
0
2. Amend appendix D to part 50 by:
0
a. Revising sections 2.2, 4.1 and 4.5.3.10;
0
b. Revising references 13. and 14. in section 6.0;
0
c. Removing figures 1., 2., and 3. in section 6.0;
0
d. Adding reference 15 in section 6.0; and
0
e. Adding section ``7.0 Figures.''.
The revisions and addition read as follows:
Appendix D to Part 50--Reference Measurement Principle and Calibration
Procedure for the Measurement of Ozone in the Atmosphere
(Chemiluminescence Method)
* * * * *
2.0 Measurement Principle.
* * * * *
2.2 The measurement system is calibrated by referencing the
instrumental chemiluminescence measurements to certified O3
standard concentrations generated in a dynamic flow system and assayed
by ultraviolet (UV) photometry to be traceable to a National Institute
of Standards and Technology (NIST) standard reference photometer for
O3 (see section 4, Calibration Procedure, below) with a
specified ozone absorption cross-section value. The absorption cross-
section value stated in section 4.1 and section 4.5.3.10 of this
appendix (304.39 atm-1 cm-1 0.94
atm-1 cm-1) will be implemented January 1, 2025,
with an additional year to complete implementation (January 1, 2026).
Until January 1, 2025, the previous ozone absorption cross-section
value, 308 4
[[Page 70599]]
atm-1 cm-1, will be used. After January 1, 2025,
both cross-section values, 304.39 0.94 atm-1
cm-1 and 308 4 atm-1
cm-1, may be used. After January 1, 2026, only the cross-
section value of 304.39 0.94 atm-1
cm-1 may be used.
* * * * *
4.0 Calibration Procedure.
4.1 Principle. The calibration procedure is based on the
photometric assay of O3 concentrations in a dynamic flow
system. The concentration of O3 in an absorption cell is
determined from a measurement of the amount of 254 nm light absorbed by
the sample. This determination requires knowledge of (1) the absorption
coefficient ([alpha]) of O3 at 254 nm, (2) the optical path
length (l) through the sample, (3) the transmittance of the sample at a
nominal wavelength of 254 nm, and (4) the temperature (T) and pressure
(P) of the sample. The transmittance is defined as the ratio I/
I0, where I is the intensity of light which passes through
the cell and is sensed by the detector when the cell contains an
O3 sample, and I0 is the intensity of light which
passes through the cell and is sensed by the detector when the cell
contains zero air. It is assumed that all conditions of the system,
except for the contents of the absorption cell, are identical during
measurement of I and I0. The quantities defined above are
related by the Beer-Lambert absorption law,
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR12OC23.000
Where:
[alpha] = absorption coefficient of O3 at 254 nm = 304.39
atm-1 cm-1, with an uncertainty of 0.94
atm-1 cm-1 at 0 [deg]C and 1 atm.
1, 2, 3, 4, 5, 6, 7, 15
c = O3 concentration in atmospheres, and
l = optical path length in cm.
A stable O3 generator is used to produce O3
concentrations over the required calibration concentration range. Each
O3 concentration is determined from the measurement of the
transmittance (I/I0) of the sample at 254 nm with a
photometer of path length l and calculated from the equation,
[GRAPHIC] [TIFF OMITTED] TR12OC23.001
The calculated O3 concentrations must be corrected for
O3 losses, which may occur in the photometer, and for the
temperature and pressure of the sample.
* * * * *
4.5 Procedure.
* * * * *
4.5.3.10. Calculate the O3 concentration from equation
4. An average of several determinations will provide better precision.
[GRAPHIC] [TIFF OMITTED] TR12OC23.002
Where:
[O3]OUT = O3 concentration, ppm
[alpha] = absorption coefficient of O3 at 254 nm = 304.39
atm-1 cm-1 at 0 [deg]C and 1 atm
l = optical path length, cm
T = sample temperature, K
P = sample pressure, torr
L = correction factor for O3 losses from 4.5.2.5 = (1-
fraction of O3 lost).
Note: Some commercial photometers may automatically evaluate all
or part of equation 4. It is the operator's responsibility to verify
that all of the information required for equation 4 is obtained,
either automatically by the photometer or manually. For
``automatic'' photometers which evaluate the first term of equation
4 based on a linear approximation, a manual correction may be
required, particularly at higher O3 levels. See the photometer
instruction manual and Reference 13 for guidance.
* * * * *
6.0 References.
* * * * *
13. Technical Assistance Document for the Calibration of Ambient
Ozone Monitors, EPA publication number EPA-454/B-22-003, January 2023.
14. QA Handbook for Air Pollution Measurement Systems--Volume II.
Ambient Air Quality Monitoring Program. EPA-454/B-17-001, January 2017.
[[Page 70600]]
15. Hodges, J.T., Viallon, J., Brewer, P.J., Drouin, B.J.,
Gorshelev, V., Janssen, C., Lee, S., Possolo, A., Smith, M.A.H.,
Walden, and Wielgosz, R.I., Recommendation of a consensus value of the
ozone absorption cross-section at 253.65 nm based on a literature
review, Metrologia, 56 (2019) 034001. [Available at https://doi.org/10.1088/1681-7575/ab0bdd.]
7.0 Figures.
[GRAPHIC] [TIFF OMITTED] TR12OC23.003
Figure 1. Gas-phase chemiluminescence analyzer schematic diagram, where
PMT means photomultiplier tube.
[[Page 70601]]
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Figure 2. Schematic diagram of a typical UV photometric calibration
system.
[[Page 70602]]
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Figure 3. Schematic diagram of a typical UV photometric calibration
system (Option 1).
[FR Doc. 2023-22531 Filed 10-11-23; 8:45 am]
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