Document ID: EPA-HQ-OAR-2022-0007-0001
Agency: epa
Document Type: Proposed Rule
Title: Reference Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere (Chemiluminescence Method)
Posted Date: 2023-02-24T05:00Z

[Federal Register Volume 88, Number 37 (Friday, February 24, 2023)]
[Proposed Rules]
[Pages 11835-11842]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-03578]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 50

[EPA-HQ-OAR-2022-0007; FRL 9344-01-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: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to 
update 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 would be any consistent 
measurable and predictable effect on reported data. The EPA is also 
proposing to update the dates of publication for two references, add a 
new reference for the updated cross-section value, and move the figures 
inadvertently placed in Section 6.0 References to a new Section 7.0 
Figures.

DATES: Comments must be received on or before March 27, 2023.
    Public hearing: If requested by March 1, 2023, the EPA will hold a 
virtual public hearing on March 17, 2023. Please refer to the 
SUPPLEMENTARY INFORMATION section for additional information on the 
public hearing.

ADDRESSES: 
    Comments. You may send your comments, identified by Docket ID No. 
EPA-HQ-OAR-2022-0007, by any of the following methods:
     Federal eRulemaking Portal:https://www.regulations.gov/ 
(our preferred method). Follow the online instructions for submitting 
comments.
     Email: [email protected]. Include Docket ID No. EPA-
HQ-OAR-2022-0007 in the subject line of the message.
     Mail: U.S. Environmental Protection Agency, EPA Docket 
Center, Air and Radiation Docket, Mail Code 28221T, 1200 Pennsylvania 
Avenue NW, Washington, DC 20460.
     Hand Delivery or Courier (by scheduled appointment only): 
EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution 
Avenue NW, Washington, DC 20004. The Docket Center's hours of 
operations are 8:30 a.m.--4:30 p.m., Monday-Friday (except Federal 
Holidays).
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the ``Public Participation'' 
heading of the SUPPLEMENTARY INFORMATION section of this document.

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: The supplementary information in this 
preamble is organized as follows:

I. Public Participation
    A. Written Comments
    B. Participation in Virtual Public Hearing
II. Background and Proposal
III. Statutory and Executive Orders Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism

[[Page 11836]]

    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

I. Public Participation

A. Written Comments

    Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2022-
0007, at https://www.regulations.gov (our preferred method), or the 
other methods identified in the ADDRESSES section. Once submitted, 
comments cannot be edited or removed from the docket. The EPA may 
publish any comment received to its public docket. Do not submit to 
EPA's docket at https://www.regulations.gov any information you 
consider to be Confidential Business Information (CBI), Proprietary 
Business Information (PBI), or other information whose disclosure is 
restricted by statute. Multimedia submissions (audio, video, etc.) must 
be accompanied by a written comment. The written comment is considered 
the official comment and should include discussion of all points you 
wish to make. The EPA will generally not consider comments or comment 
contents located outside of the primary submission (i.e., on the web, 
cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the 
full EPA public comment policy; information about CBI, PBI, or 
multimedia submissions; and general guidance on making effective 
comments.

B. Participation in Virtual Public Hearing

    The EPA will begin pre-registering speakers for the hearing upon 
publication of this document in the Federal Register. To register to 
speak at the virtual hearing, please contact Ms. Joann Rice at (919) 
541-3372 or [email protected]. The last day to pre-register to speak 
at the hearing will be March 10, 2023. On March 16, 2023, the EPA will 
post a general agenda for the hearing that will list pre-registered 
speakers in approximate order at: https://www.epa.gov/amtic.
    The EPA will make every effort to follow the schedule as closely as 
possible on the day of the hearing; however, please plan for the 
hearings to run either ahead of schedule or behind schedule.
    The EPA encourages commenters to provide the EPA with a copy of 
their oral testimony electronically by emailing it to 
[email protected]. The EPA also recommends submitting the text of your 
oral comments as written comments to the rulemaking docket.
    The EPA may ask clarifying questions during the oral presentations 
but will not respond to the presentations at that time. Written 
statements and supporting information submitted during the comment 
period will be considered with the same weight as oral comments and 
supporting information presented at the public hearing.
    Please note that any updates made to any aspect of the hearing are 
posted online at https://www.epa.gov/amtic. While the EPA expects the 
hearing to go forward as set forth above, please monitor our website or 
contact Ms. Joann Rice at (919) 541-3372 or [email protected] to 
determine if there are any updates. The EPA does not intend to publish 
a document in the Federal Register announcing updates.

II. Background and Proposal

    In 1961, the ozone absorption cross-section was measured to be 
1.1476 x10-\17\ cm\2\ molecule-\1\ or 308.3 
atm-\1\ cm-\1\ with a reported relative standard 
uncertainty of 1.4% (Hearn, 1961). 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 through a 
hierarchy of standards to a NIST-made ozone SRP. Efforts to improve the 
accuracy of the ozone absorption cross-section have continued over 
several years and rigorous assessment of the bias and uncertainty in 
the value became a high priority.
    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 to be adopted in standard UV 
photometric instruments, including the SRP, for measurements of ozone 
concentrations (Hodges et al., 2019).
    After publication in Hodges et al., 2019, the CCQM-GAWG \1\ 
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 uncertainty and is an advancement and improvement in 
the UV photometer measurement method.
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    \1\ 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 atmosphere atm-\1\ 
cm-\1\. The proposed revision would change the ozone 
absorption cross-section and amend relevant references to align 
internationally with the BIPM CCQM-GAWG's updated 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 would result in an improvement in the accuracy of 
surface ozone monitoring measurements by reducing uncertainty and is 
seeking comment on our proposed change from the UV absorption cross-
section value in Appendix D of Part 50 to this more accurate consensus 
value.
    The new value would reduce the uncertainty to 0.31% from the 
current 1.4%. The new value would also be 1.2% lower than the current 
value, a change that could result in increases in measured ozone 
concentrations. However, there are several factors that EPA believes 
would make it unlikely that this change would 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

[[Page 11837]]

Ambient Air Quality Standards for Ozone.''
    Multiple factors can contribute to variability in monitoring data, 
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,\2\ data handling and computation procedures in Appendix U, 
and meteorology.
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    \2\ 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 would be achieved through software/firmware 
modification and would not require any hardware changes. The EPA is 
proposing to modify the EPA SRPs simultaneously, versus 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 two 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 would 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 measurement uncertainty for ozone in 40 CFR part 58, 
``Ambient Air Quality Surveillance,'' for an annual measurement 
uncertainty 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%.\3\ The 1.2% change is, therefore, within the national precision 
and less than the national bias.
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    \3\ 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 \4\ 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 and 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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    \4\ 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 is 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 
calibration.
    Design values are the 3-year average of the annual 4th highest 
daily maximum 8-hour value measured at each monitoring site. If the 
proposed cross-section value is timely adopted, design values for 2026 
will have all three years (2024-2026) of monitoring data generated with 
the new cross-section value. Design values for 2024 will have one year 
based on the new value, and design values for 2025 will have two years 
of monitoring data generated with the new value. 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 this proposed change 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 of 
today's proposal on 3-year design values.
    Taking these factors into consideration, EPA believes it is 
unlikely that the proposed 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 
would improve the accuracy of measured

[[Page 11838]]

ozone values, but would be unlikely to have a measurable, predictable 
influence on any given monitor or design value, the EPA supports and 
proposes 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\.

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 13563: Improving Regulation and Regulatory Review

    This action is not a significant regulatory action and was, 
therefore, not submitted to the Office of Management and Budget (OMB) 
for review.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA. This action proposes to revise 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 proposed action would update 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 proposes updates to 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.

References

Hearn A. G. (1961). Absorption of ozone in ultra-violet and visible 
regions of spectrum Proc. Phys. Soc. 78 932-40
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.

List of Subjects 40 CFR Part 50

    Environmental protection, Air pollution control, Ozone.

Michael S. Regan,
Administrator.

    For the reasons set forth in the preamble, the EPA proposes to 
amend 40 CFR part 50 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. In Section 4.0, revising paragraphs 4.1 and 4.5.3.10;
0
b. In Section 6.0, revising references 12 and 14, removing figures 1, 2 
and 3, adding reference 15; and
0
c. Adding new Section 7.0.
    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)

* * * * *

[[Page 11839]]

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,
[GRAPHIC] [TIFF OMITTED] TP24FE23.098

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] TP24FE23.099

    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.
* * * * *
    4.5.3.10. Calculate the O3 concentration from equation 
4. An average of several determinations will provide better precision.
[GRAPHIC] [TIFF OMITTED] TP24FE23.100

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

* * * * *
12. Transfer Standards for Calibration of Ambient Air Monitoring 
Analyzers for Ozone, EPA publication number EPA-454/B-22-003, December 
2022.
* * * * *
14. QA Handbook for Air Pollution Measurement Systems--Volume II. 
Ambient Air Quality Monitoring Program. EPA-454/B-17-001, January 2017.
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.]

[[Page 11840]]

7.0 Figures
[GRAPHIC] [TIFF OMITTED] TP24FE23.101

Figure 1 of Section 7 to Appendix D of Part 50--Gas-phase 
chemiluminescence analyzer schematic diagram, where PMT means 
photomultiplier tube.

[[Page 11841]]

[GRAPHIC] [TIFF OMITTED] TP24FE23.102

Figure 2 of Section 7 to Appendix D of Part 50--Schematic diagram of a 
typical UV photometric calibration system.

[[Page 11842]]

[GRAPHIC] [TIFF OMITTED] TP24FE23.103

Figure 3 of Section 7 to Appendix D of Part 50--Schematic diagram of a 
typical UV photometric calibration system (Option 1).

[FR Doc. 2023-03578 Filed 2-23-23; 8:45 am]
BILLING CODE 6560-50-P