[Federal Register Volume 87, Number 225 (Wednesday, November 23, 2022)]
[Rules and Regulations]
[Pages 72312-72357]
[FR Doc No: 2022-25134]

Vol. 87

Wednesday,

No. 225

November 23, 2022

Part III

Environmental Protection Agency

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40 CFR Parts 9, 87, 1030, et al.

Control of Air Pollution From Aircraft Engines: Emission Standards and
Test Procedures; Final Rule

Federal Register / Vol. 87, No. 225 / Wednesday, November 23, 2022 /
Rules and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 9, 87, 1030, and 1031

[EPA-HQ-OAR-2019-0660; FRL-7558-02-OAR]
RIN 2060-AU69

Control of Air Pollution From Aircraft Engines: Emission
Standards and Test Procedures

AGENCY: Environmental Protection Agency (EPA)

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is finalizing
particulate matter (PM) emission standards and test procedures
applicable to certain classes of engines used by civil subsonic jet
airplanes (engines with rated output of greater than 26.7 kilonewtons
(kN)) to replace the existing smoke standard for those engines. The EPA
is adopting these standards under our authority in the Clean Air Act
(CAA). These standards and test procedures are equivalent to the engine
standards adopted by the United Nations' International Civil Aviation
Organization (ICAO) in 2017 and 2020 and will apply to both new type
design aircraft engines and in-production aircraft engines. The EPA, as
well as the U.S. Federal Aviation Administration (FAA), actively
participated in the ICAO proceedings in which the ICAO requirements
were developed. These standards reflect the importance of the control
of PM emissions and U.S. efforts to secure the highest practicable
degree of uniformity in aviation regulations and standards.
Additionally, the EPA is migrating, modernizing, and streamlining the
existing regulations into a new part in the Code of Federal
Regulations. As part of this update, the EPA is also aligning with ICAO
by applying the smoke number standards to engines less than or equal to
26.7 kilonewtons rated output used on supersonic airplanes.

DATES: This final rule is effective on December 23, 2022. The
incorporation by reference of certain material listed in this rule is
approved by the Director of the Federal Register as of December 23,
2022.

ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-OAR-2019-0660. All documents in the docket are
listed on the www.regulations.gov website. Although listed in the
index, some information is not publicly available, e.g., confidential
business information 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 either electronically through www.regulations.gov or in hard
copy at the EPA Docket Center, WJC West Building, Room 3334, 1301
Constitution Ave. NW, Washington, DC. The Docket Center's hours of
operations are 8:30 a.m.-4:30 p.m., Monday-Friday (except Federal
Holidays). For further information on the EPA Docket Center services
and the current status, see: https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Bryan Manning, Office of
Transportation and Air Quality, Assessment and Standards Division
(ASD), Environmental Protection Agency, 2000 Traverwood Drive, Ann
Arbor, MI 48105; telephone number:<PHONE_NUMBER>; email address:
[email protected].

SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information
    A. Does this action apply to me?
    B. Executive Summary
    C. EPA Future Work on Aircraft Engine PM Standards Beyond the
Scope of This Final Rule
    D. Judicial Review, Administrative Reconsideration, and
Severability
II. Introduction: Context for This Action
    A. The EPA Statutory Authority and Responsibilities Under the
Clean Air Act
    B. The Role of the United States in International Aircraft
Agreements
    C. The Relationship Between the EPA's Regulation of Aircraft
Engine Emissions and International Standards
III. Particulate Matter Impacts on Air Quality and Health
    A. Background on Particulate Matter
    B. Health Effects of Particulate Matter
    C. Environmental Effects of Particulate Matter
    D. Near-Source Impacts on Air Quality and Public Health
    E. Contribution of Aircraft Emissions to PM in Selected Areas
    F. Other Pollutants Emitted by Aircraft
    G. Environmental Justice
IV. Details of the Rule
    A. PM Mass Standards for Aircraft Engines
    B. PM Number Standards for Aircraft Engines
    C. PM Mass Concentration Standard for Aircraft Engines
    D. Test and Measurement Procedures
    E. Annual Reporting Requirement
    F. Response to Key Comments
V. Aggregate PM Inventory Methodology and Impacts
    A. Aircraft Engine PM Emissions Modeling Methodologies
    B. PM Emission Inventory
    C. Projected Reductions in PM Emissions
VI. Technological Feasibility and Economic Impacts
    A. Market Considerations
    B. Conceptual Framework for Technology
    C. Technological Feasibility
    D. Costs Associated With the Rule
    E. Summary of Benefits and Costs
VII. Technical Amendments
    A. Migration of Regulatory Text to New Part
    B. Deletion of Unnecessary Provisions
    C. Other Technical Amendments and Minor Changes
VIII. Statutory Authority and Executive Order 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
    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) and
1 CFR Part 51
    J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations
    K. Congressional Review Act

I. General Information

A. Does this action apply to me?

    This action will potentially affect companies that design and/or
manufacture civil subsonic jet aircraft engines with a rated output of
greater than 26.7 kN and those that design and/or manufacture civil jet
engines with a rated output at or below 26.7 kN for use on supersonic
airplanes. These potentially affected entities include the following:

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                                                        Examples of
            Category              NAICS code \a\   potentially affected
                                                         entities
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Industry.......................          336412   Manufacturers of new
                                                   aircraft engines.
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\a\ North American Industry Classification System (NAICS).

    This table lists the types of entities that the EPA is now aware
could potentially be affected by this action. Other types of entities
not listed in the table could also be regulated. To determine whether
your activities are regulated by this action, you should carefully
examine the relevant applicability criteria in 40 CFR parts 87, 1030,
and 1031. If you have any questions regarding the applicability of this
action to a particular entity, consult the person listed in the
preceding FOR FURTHER INFORMATION CONTACT section.
    For consistency purposes across the U.S. Code of Federal
Regulations (CFR), common definitions for the words ``airplane,''
``aircraft,'' ``aircraft engine,'' and ``civil aircraft'' are found at
14 CFR 1.1 and are used as appropriate throughout this new regulation
under 40 CFR parts 87, 1030, and 1031.

B. Executive Summary

1. Summary of the Major Provisions of the Regulatory Action
    The EPA is regulating PM emissions from certain aircraft engines
through the adoption of domestic PM regulations that match the ICAO PM
standards, which will be implemented and enforced in the United States.
The covered engines are subsonic turbofan and turbojet aircraft engines
with rated output (maximum thrust available for takeoff) of greater
than 26.7 kN. These aircraft engines are used by civil subsonic jet
airplanes generally for the purpose of commercial passenger and freight
aircraft, as well as larger business jets. The EPA is adopting three
different forms of PM standards: a PM mass standard in milligrams per
kilonewton (mg/kN), a PM number standard in number of particles per
kilonewton (#/kN), and a PM mass concentration standard in micrograms
per cubic meter ([micro]g/m\3\). The applicable dates and coverage of
these standards vary, as described in the following paragraphs, and
more fully in sections IV.A, IV.B, and IV.C respectively.
    First, the EPA is finalizing PM engine emission standards, in the
form of both PM mass (mg/kN) and PM number (#/kN), for both new type
design and in-production covered engines. The standards for in-
production engines apply to those engines that are manufactured on or
after January 1, 2023. The standards for new type designs apply to
those engines whose initial type certification application is submitted
on or after January 1, 2023. The in-production standards have different
emission levels limits than the standards for new type designs. The
different emission limits for new type designs and in-production
engines depend on the rated output of the engines. Compliance with the
PM mass and number standards will be done in accordance with the
standard landing and take-off (LTO) test cycle, which is currently used
for demonstrating compliance with gaseous emission standards (oxides of
nitrogen (NOX), hydrocarbons (HC), and carbon monoxide (CO)
standards) for the covered engines.
    Second, the EPA is adopting a PM engine emission standard in the
form of maximum mass concentration ([micro]g/m\3\) for covered engines
manufactured on or after January 1, 2023.\1\ Compliance with the PM
mass concentration standard will be done using the same test data that
is developed to demonstrate compliance with the LTO-based PM mass and
number standards. The PM mass concentration standard applies to the
highest concentration of PM measured across the engine operating thrust
range, not just at one of the four LTO thrust settings.
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    \1\ The implementation date for ICAO's PM maximum mass
concentration standards is on or after January 1, 2020. The PM
maximum mass concentration standards finalized in this action will
have an implementation date of January 1, 2023 (instead of January
1, 2020).
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    The PM mass concentration standard was developed by ICAO to
provide, through a PM mass measurement, the equivalent smoke opacity or
visibility control as afforded by the existing smoke number standard
for the covered engines. Thus, the EPA is no longer applying the
existing smoke number standard for new engines that will be subject to
the PM mass concentration standard after January 1, 2023, but the EPA
is maintaining smoke number standards for new engines not covered by
the PM mass concentration standard (e.g., in-production aircraft
turbofan and turbojet engines with rated output less than or equal to
26.7 kN) and for engines already manufactured. This approach will
essentially change the existing standard for covered engines from being
based on a smoke measurement to a PM measurement.
    Third, the EPA is finalizing testing and measurement procedures for
the PM emission standards and various updates to the existing gaseous
exhaust emissions test procedures. These test procedure provisions will
implement the recent additions and amendments to the ICAO's
regulations, which are codified in ICAO Annex 16, Volume II. As we have
historically done, we are incorporating these test procedure additions
and amendments to the ICAO Annex 16, Volume II into our regulations by
reference.
    The aircraft engine PM standards, test procedures and associated
regulatory requirements are equivalent to the international PM
standards and test procedures adopted by ICAO in 2017 and 2020 and
promulgated in Annex 16, Volume II.\2\ The United States and other
member States of ICAO, as well as the world's aircraft engine
manufacturers and other interested stakeholders, participated in the
deliberations leading up to ICAO's adoption of the international
aircraft engine PM emission standards.
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    \2\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017. Available at https://www.icao.int/publications/catalogue/cat_2022_en.pdf (last accessed
October 31, 2022). The ICAO Annex 16 Volume II is found on page 17
of the ICAO Products & Services Catalog, English Edition of the 2022
catalog, and it is copyright protected; Order No. AN16-2. The ICAO
Annex 16, Volume II, Fourth Edition, includes Amendment 10 of
January 1, 2021. Amendment 10 is also found on page 17 of this ICAO
catalog, and it is copyright protected; Order No. AN 16-2/E/12.
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    In addition to the PM standards just discussed, the EPA is
migrating most of the existing aircraft engine emissions regulations
from 40 CFR part 87 to a new 40 CFR part 1031, and all the aircraft
engine standards and requirements are specified in this new 40 CFR part
1031. Along with this migration, the EPA is restructuring the
regulations to allow for better ease of use and allow for more
efficient future updates. The EPA is also deleting some unnecessary
definitions and regulatory provisions. Finally, the EPA is adopting
several other minor technical amendments to the regulations, including
applying smoke number standards to engines of less than or equal to
26.7 kilonewtons (kN) rated output used in supersonic airplanes.
2. Purpose of the Regulatory Action
    In developing these standards, the EPA took into consideration the
Agency's legal authority and the explicit requirements under CAA
section 231, including those relating to safety, noise, lead time and
costs. The EPA further considered the importance of controlling PM
emissions, international harmonization of aviation requirements, and
the international nature of the aircraft industry and air travel. In
addition, the EPA gave significant weight to the United States' treaty
obligations under the Chicago Convention, as discussed in Section II.B,
in determining the need for and appropriate levels of PM standards.
These considerations led the EPA to conclude that adopting standards
for PM emissions from certain classes of

covered aircraft engines that are equivalent in scope, stringency, and
effective date to the PM standards adopted by ICAO are appropriate at
this time.
    One of the core functions of ICAO is to adopt Standards and
Recommended Practices on a wide range of aviation-related matters,
including aircraft emissions. As a member State of ICAO, the United
States actively participates in the development of new environmental
standards, within ICAO's Committee on Aviation Environmental Protection
(CAEP), including the PM standards adopted by ICAO in both 2017 and
2020. Due to the international nature of the aviation industry, there
is an advantage to working within ICAO to secure the highest
practicable degree of uniformity in international aviation regulations
and standards. Uniformity in international aviation regulations and
standards is a goal of the Chicago Convention, because it ensures that
passengers and the public can expect similar levels of protection for
safety and human health and the environment regardless of manufacturer,
airline, or point of origin of a flight. Further, it helps reduce
barriers in the global aviation market, benefiting both U.S. aircraft
engine manufacturers and consumers.
    When developing new emission standards, ICAO/CAEP seeks to capture
the technological advances made in the control of emissions through the
adoption of anti-backsliding standards reflecting the current state of
technology. The PM standards that the EPA is adopting were developed
using this approach. Thus, the adoption of these aviation standards
into U.S. law will simultaneously prevent aircraft engine PM levels
from increasing beyond their current levels, align U.S. domestic
standards with the ICAO standards for international harmonization, and
meet the United States' treaty obligations under the Chicago
Convention.
    These standards will also allow U.S. manufacturers of covered
aircraft engines to remain competitive in the global marketplace (as
described in Section IV). In the absence of U.S. standards implementing
the ICAO aircraft engine PM emission standards, U.S. civil aircraft
engine manufacturers could be forced to seek PM emissions certification
from an aviation certification authority of another country (not the
FAA) to market and operate their aircraft engines internationally. U.S.
manufacturers could be at a significant disadvantage if the United
States fails to adopt standards that are at least as stringent as the
ICAO standards for PM emissions. The ICAO aircraft engine PM emission
standards have been adopted by other ICAO member states that certify
aircraft engines.\3\ The action to adopt in the U.S. PM standards that
match the ICAO standards will help ensure international consistency and
acceptance of U.S.-manufactured engines worldwide.
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    \3\ Aside from the FAA in the United States, the only other
civil aviation authorities that routinely certify airplane engines
are Transport Canada and the European Union Aviation Safety Agency,
both of which have already adopted the ICAO airplane engine
particulate matter emission standards.
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3. Environmental Justice
    The EPA defines environmental justice as the fair treatment and
meaningful involvement of all people regardless of race, color,
national origin, or income with respect to the development,
implementation, and enforcement of environmental laws, regulations, and
policies. Section III.G discusses the potential environmental justice
concerns associated with exposure to aircraft PM near airports.
    Studies have reported that many communities in close proximity to
airports are disproportionately represented by people of color and low-
income populations (as described in Section III.G). Separate from this
rulemaking, the EPA is conducting an analysis of communities residing
near airports where jet aircraft operate to more fully understand
disproportionately high and adverse human health or environmental
effects on people of color, low-income populations, and/or Indigenous
peoples. The results of this analysis could help inform additional
policies to reduce pollution in communities living in close proximity
to airports.
    As described in Section V.C, while newer aircraft engines typically
have significantly lower emissions than existing aircraft engines, the
standards in this final rule are technology-following to align with
ICAO's standards and are not expected to, in and of themselves, result
in further reductions in PM from these engines. Therefore, we do not
anticipate the standards to result in an improvement in air quality for
those who live near airports where these aircraft operate.

C. EPA Future Work on Aircraft Engine PM Standards Beyond the Scope of
This Final Rule

    While the EPA believes that adopting PM standards that match those
developed and adopted by ICAO is the proper course of action in this
final rule, the EPA views the standards adopted in this action as just
one appropriate step in our efforts to control PM emissions from
aircraft engines. Consistent with our statutory authority, which
directs the EPA to issue, and permits the EPA to revise, standards
``from time to time,'' CAA section 231(a)(2)(A) and (a)(3), after
consultation with the FAA (CAA section 231(a)(2)(B)(i)), the EPA views
our regulation of aircraft PM emissions as a long-term process, with
the potential for successive standards of increasing stringency. Future
stringencies may include technology-forcing standards, where
appropriate, provided that such standards do not significantly increase
noise and adversely affect safety in accordance with CAA section
231(a)(2)(B)(ii). The EPA intends to continue to assess available
emission control technologies and associated lead times, so that if the
EPA were to pursue more stringent standards in the future, the EPA
would provide the necessary time to permit the development and
application of the requisite technology--giving appropriate
consideration to the cost of compliance within such period.
    The EPA continues to believe that ICAO is the most appropriate
venue in which to undertake such work. To that end, the U.S. delegation
to ICAO/CAEP, with significant input from EPA, developed a position
paper to the CAEP/12 meeting in February 2022.\4\ In this paper, the
United States proposed several topics for CAEP to consider for future
work on emissions items. Among the U.S. proposals was a call to update
the PM standards beyond those already adopted by CAEP that would
reflect best available technologies for future, to-be-developed,
standards. The United States also proposed work to develop an updated
metric to improve the effectiveness of future NOX emission
standards, as well as an integrated standards-setting process to
simultaneously update both PM and NOX standards for aircraft
engines given the strong interdependency between engine NOX
and PM levels.\5\ The EPA also advocated for improved modeling
techniques that would better reflect the costs and emission reductions
and better inform decision making around proposed CAEP emission
standard levels.
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    \4\ U.S. EPA, Mueller, J. Memorandum to Docket ID No. EPA-HQ-
OAR-2019-0660, ``United States Position Papers to CAEP/12 Meeting,''
August 19, 2022.
    \5\ In this context, the metric is the form of the standard (in
this case, mass of pollutant per unit of thrust), as well as the
form of the regulatory limit line and any correlating parameters
included. In the case of aircraft engine NOX, the
regulatory limit line is a function of engine overall pressure
ratio.

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    CAEP did not accept the U.S. request to work on updated aircraft
engine NOX and PM standards during the current CAEP/13 cycle
due to concerns that the resources needed for such work would
negatively impact efforts to update the international airplane
CO2 and noise standards. However, work on an improved
NOX metric was approved and is underway this CAEP cycle,
with an understanding that it is laying the groundwork for a potential
update of the NOX and PM standards during the next CAEP
cycle.\6\ Further, improving the cost and emission reduction modeling
methodology has been agreed to as a work item for this CAEP cycle. The
EPA is actively working within CAEP on both these efforts, and the EPA
will continue to advocate for efforts in CAEP that will result in the
development of future PM emission standards which reflect best
available technologies.
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    \6\ ICAO, 2022: Committee on Aviation Environmental Protection
(CAEP), Report of the Twelfth Meeting, Montreal, February 7-17,
2022, Doc 10176, CAEP/12.
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D. Judicial Review, Administrative Reconsideration, and Severability

    This final action is ``nationally applicable'' within the meaning
of CAA section 307(b)(1) because it is expressly listed in the section
(i.e., ``any standard under section [231] of this title''). Under CAA
section 307(b)(1), petitions for judicial review of this action must be
filed in the U.S. Court of Appeals for the District of Columbia Circuit
within 60 days from the date this final action is published in the
Federal Register. Filing a petition for reconsideration by the
Administrator of this final action does not affect the finality of the
action for the purposes of judicial review, nor does it extend the time
within which a petition for judicial review must be filed and shall not
postpone the effectiveness of such rule or action. Under CAA section
307(b)(2), the requirements established by this final rule may not be
challenged separately in any civil or criminal proceedings brought by
the EPA to enforce the requirements.
    CAA section 307(d)(7)(B) further provides that only an objection to
a rule or procedure which was raised with reasonable specificity during
the period for public comment (including any public hearing) may be
raised during judicial review. This section also provides a mechanism
for the EPA to reconsider the rule if the person raising an objection
can demonstrate to the Administrator that it was impracticable to raise
such objection within the period for public comment or if the grounds
for such objection arose after the period for public comment (but
within the time specified for judicial review) and if such objection is
of central relevance to the outcome of the rule. Any person seeking to
make such a demonstration should submit a Petition for Reconsideration
to the Office of the Administrator, U.S. EPA, Room 3000, WJC South
Building, 1200 Pennsylvania Ave. NW, Washington, DC 20460, with a copy
to both the person listed in the FOR FURTHER INFORMATION CONTACT
section, and the Associate General Counsel for the Air and Radiation
Law Office, Office of General Counsel (Mail Code 2344A), U.S. EPA, 1200
Pennsylvania Ave. NW, Washington, DC 20460. In addition, the EPA
requests that an electronic copy of the Petition for Reconsideration
also be sent to the person listed in the FOR FURTHER INFORMATION
CONTACT section.
    The following portions of this rulemaking are mutually severable
from each other: (1) the PM mass concentration standard in Section
IV.C; (2) the PM mass and number standards in sections IV.A and IV.B;
(3) the test and measurement procedures in Section IV.D; (4) the
reporting requirements in Section IV.E; (5) those changes to 40 CFR
parts 87 and 1031 described in Section VII that are not intended solely
to implement the new PM standards; and (6) the changes to 40 CFR part
1030 described in Section VII.C.\7\ The PM mass concentration standard
and the PM mass and number standards serve different purposes, as
described in more detail in Section IV. The reporting requirements
(including those for PM) in Section IV.E predate this final rule as
they were established by a prior Information Collection Request and are
simply being added to the CFR in this action for the convenience of the
entity required to provide a production report. Similarly, while the
test and measurement procedures in Section IV.D will be used in
determining compliance with the new PM standards, they are not
dependent on the PM standards, and they are also required to be used to
comply with the reporting requirements separate from the actual PM
standards. The regulatory migration and other technical amendments in
Section VII are not related to the implementation of the new PM
standards. If any of the portions of this rule the EPA has identified
as mutually severable from each other are vacated by a reviewing court,
the EPA intends for the portions of this rule which are not vacated by
a reviewing court to remain effective, and would only take action to
remove the portions of the rule which are vacated from the CFR, leaving
the other portions of the rule in effect.\8\ Finally, if a reviewing
court were to vacate the PM mass concentration standard in Section
IV.C, the EPA intends to reinstate the smoke number standard contained
in 40 CFR 1031.60(a)(5) for engines with a rated output of greater than
26.7 kN, such that the smoke number standard would go back into effect
for those engines.
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    \7\ Certain portions may also be internally severable.
    \8\ The EPA considers those sections of regulatory text which
are included only to implement the new PM standards to all be within
40 CFR part 1031. Specifically, the regulatory text solely related
to implementing the PM mass concentration standard is contained in
Sec. Sec.  1031.30(a)(2)(ii), 1031.60(a)(6), and 1031.130(c)(1)(v),
as well as the phrase ``before January 1, 2023'' in Sec.
1031.60(a)(5), while the regulatory text solely related to
implementing the PM mass and number standards is contained in
Sec. Sec.  1031.30(a)(2)(iii) and (iv), 1031.60(b), and
1031.130(c)(1)(vi) and (vii). All other regulatory changes are
severable from the PM standards and are intended to remain in effect
if any of the PM standards were to be set aside by a reviewing
court.
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II. Introduction: Context for This Action

    The EPA has been regulating PM emissions from aircraft engines
since the 1970s when the first smoke number standards were adopted.
This section provides context for the final rule, which adopts three PM
standards for aircraft engines (a PM mass standard, a PM number
standard, and a PM mass concentration standard). This section includes
a description of the EPA's statutory authority, the U.S. role in ICAO
and developing international emission standards, and the relationship
between the U.S. standards and the ICAO international standards.

A. The EPA's Statutory Authority and Responsibilities Under the Clean
Air Act

    CAA section 231(a)(2)(A) directs the Administrator of the EPA to,
from time to time, propose aircraft engine emission standards
applicable to the emission of any air pollutant from classes of
aircraft engines which in his or her judgment causes or contributes to
air pollution that may reasonably be anticipated to endanger public
health or welfare.\9\ CAA section 231(a)(2)(B) directs the EPA to
consult with the Administrator of the Federal Aviation Administration
(FAA) on such standards, and it prohibits the EPA from changing
aircraft emission standards if such a change would significantly
increase noise and adversely affect safety.\10\ CAA section 231(a)(3)
provides that after we provide notice and an opportunity for a public
hearing on standards, the Administrator shall issue such standards
``with such modifications as he deems

appropriate.'' \11\ In addition, under CAA section 231(b) the EPA is
required to ensure, in consultation with the U.S. Department of
Transportation (DOT), that the effective date of any standard provides
the necessary time to permit the development and application of the
requisite technology, giving appropriate consideration to the cost of
compliance within such period.\12\
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    \9\ 42 U.S.C. 7571(a)(2)(A).
    \10\ 42 U.S.C. 7571(a)(2)(B)(i)-(ii).
    \11\ 42 U.S.C. 7571(a)(3).
    \12\ 42 U.S.C. 7571(b).
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    Consistent with its longstanding approach \13\ and the District of
Columbia (D.C.) Circuit precedent,\14\ the EPA interprets its authority
under CAA section 231 as providing the Administrator wide discretion in
determining what standards are appropriate, after consideration of the
statute and other relevant factors, such as applicable international
standards. While the statutory language of CAA section 231 is not
identical to other provisions of Title II of the CAA that direct the
EPA to establish technology-based standards for various types of mobile
sources, the EPA interprets its authority under CAA section 231 to be
similar to those provisions that authorize us to identify a reasonable
balance of specified emissions reduction, cost, safety, noise, and
other factors.\15\ However, we are not compelled under CAA section 231
to obtain the ``greatest degree of emission reduction achievable'' as
per CAA sections 202(a)(3)(A) and 213(a)(3). The EPA does not interpret
the Act as requiring the agency to give subordinate status to other
factors such as cost, safety, and noise in determining what standards
are reasonable for aircraft engines.\16\ Rather, the EPA has great
flexibility under CAA section 231 in determining what standard is most
reasonable for aircraft engines. Moreover, in light of the U.S.
ratification of the Chicago Convention, EPA has historically given
significant weight to uniformity with international requirements as a
factor in setting aircraft engine standards. The fact that most
airplanes already meet the standards does not in itself mean that the
standards are inappropriate, provided the agency has a reasonable basis
after considering all the relevant factors. By the same token, a
technology-forcing standard would not be precluded by CAA section 231,
in light of the forward-looking language of CAA section 231(b).\17\
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    \13\ See 70 FR 69664, 69676 (November 17, 2005); 86 FR 2136,
2157 (January 11, 2021).
    \14\ The U.S. Court of Appeals for the D.C. Circuit has held
that CAA section 231 confers an unusually ``broad'' degree of
discretion on EPA to ``weigh various factors'' and adopt aircraft
engine emission standards as the Agency determines are reasonable.
Nat'l Ass'n of Clean Air Agencies v. EPA, 489 F.3d 1221, 1229-30
(D.C. Cir. 2007).
    \15\ See, e.g., Husqvarna AB v. EPA, 254 F.3d 195 (D.C. Cir.
2001) (upholding the EPA's promulgation of technology-based
standards for small non-road engines under CAA section 213(a)(3)).
    \16\ Cf. Sierra Club v. EPA, 325 F.3d 374, 378-380 (D.C. Cir.
2003) (holding that even a Clean Air Act provision requiring the
``greatest emission reduction achievable'' did not bind the Agency
to weigh ``pure technological capability'' to the exclusion of other
factors like cost, lead time, safety nor ``resolve how [the EPA]
should weigh all these factors'').
    \17\ See 38 FR19088 (July 17, 1973); 41 FR 34722 (August 16,
1976); see also NACAA, 489 F.3d at 1229-30.
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    Thus, as in past rulemakings, the EPA notes its authority under the
CAA to issue reasonable aircraft engine standards with either
technology-following or technology-forcing results, provided that, in
either scenario, the Agency has a reasonable basis after considering
all the relevant factors for setting the standard.\18\ Once the EPA
adopts standards, CAA section 232 then directs the Secretary of
Transportation to prescribe regulations to ensure compliance with the
EPA's standards.\19\ Finally, CAA section 233 vests the authority to
promulgate emission standards for aircraft or aircraft engines only in
the Federal Government. States are preempted from adopting or enforcing
any standard respecting aircraft or aircraft engine emissions unless
such standard is identical to the EPA's standards.\20\
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    \18\ See 70 FR 69664, 69676 (November 17, 2005); 86 FR 2136,
2139-2140 (January 11, 2021).
    \19\ 42 U.S.C. 7572.
    \20\ 42 U.S.C. 7573.
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B. The Role of the United States in International Aircraft Agreements

    The Convention on International Civil Aviation (commonly known as
the Chicago Convention) was signed in 1944 at the Diplomatic Conference
held in Chicago. It was ratified by the United States on August 9,
1946. The Chicago Convention establishes the legal framework for the
development of international civil aviation. The primary objective is
``that international civil aviation may be developed in a safe and
orderly manner and that international air transport services may be
established on the basis of equality of opportunity and operated
soundly and economically.'' \21\ In 1947, ICAO was established, and
later in that same year, ICAO became a specialized agency of the United
Nations (UN). ICAO sets international standards for aviation safety,
security, efficiency, capacity, and environmental protection and serves
as the forum for cooperation in all fields of international civil
aviation. ICAO works with the Chicago Convention's member States and
global aviation organizations to develop international Standards and
Recommended Practices (SARPs), which member States reference when
developing their domestic civil aviation regulations. The United States
is one of 193 currently participating ICAO member
States.22 23 ICAO standards are not self-implementing. They
must first be adopted into domestic law to be legally binding in any
member State.
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    \21\ ICAO, 2006: Convention on International Civil Aviation,
Ninth Edition, Document 7300/9. Available at: http://www.icao.int/publications/Documents/7300_9ed.pdf (last accessed October 31,
2022).
    \22\ Members of ICAO's Assembly are generally termed member
States or contracting States.
    \23\ There are currently 193 contracting States (member States)
according to ICAO's website. The list of ICAO member States is
available in the docket for this rulemaking under document
identification number EPA-HQ-OAR-2019-0660-0011.
---------------------------------------------------------------------------

    In the interest of global harmonization and international air
commerce, the Chicago Convention urges its member States to
``collaborate in securing the highest practicable degree of uniformity
in regulations, standards, procedures and organization in relation to
aircraft, [. . .] in all matters which such uniformity will facilitate
and improve air navigation.'' \24\ The Chicago Convention also
recognizes that member States may adopt national standards that are
more or less stringent than those agreed upon by ICAO or standards that
are different in character or that comply with the ICAO standards by
other means. Any member State that finds it impracticable to comply in
all respects with any international standard or procedure, or that
determines it is necessary to adopt regulations or practices differing
in any particular respect from those established by an international
standard, is required to give notification to ICAO of the differences
between its own practice and that established by the international
standard.\25\
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    \24\ ICAO, 2006: Convention on International Civil Aviation,
Article 37, Ninth Edition, Document 7300/9.
    \25\ Id.
---------------------------------------------------------------------------

    ICAO's work on the environment focuses primarily on those problems
that benefit most from a common and coordinated approach on a worldwide
basis, namely aircraft noise and engine emissions. SARPs for the
certification of aircraft noise and aircraft engine emissions are
covered by Annex 16 of the Chicago Convention. To continue to address
aviation environmental issues, in 2004, ICAO established three
environmental goals: (1) limit or reduce the number of people affected
by significant aircraft noise; (2) limit or reduce the impact of
aviation emissions

on local air quality; and (3) limit or reduce the impact of aviation
greenhouse gas (GHG) emissions on the global climate.
    The Chicago Convention has a number of other features that govern
international commerce. First, member States that wish to use aircraft
in international transportation must adopt emission standards that are
at least as stringent as ICAO's standards if they want to ensure
recognition of their airworthiness certificates by other member States.
Member States may ban the use of any aircraft within their airspace
that does not meet ICAO standards.\26\ Second, the Chicago Convention
indicates that member States are required to recognize the
airworthiness certificates issued or rendered valid by the contracting
State in which the aircraft is registered provided the requirements
under which the certificates were issued are equal to or above ICAO's
minimum standards.\27\ Third, to ensure that international commerce is
not unreasonably constrained, a member State that cannot meet or deems
it necessary to adopt regulations differing from the international
standard is obligated to notify ICAO of the differences between its
domestic regulations and ICAO standards.\28\
---------------------------------------------------------------------------

    \26\ Id., Article 33.
    \27\ Id.
    \28\ Id., Article 38.
---------------------------------------------------------------------------

    ICAO's Committee on Aviation Environmental Protection (CAEP), which
consists of members and observers from States as well as
intergovernmental and non-governmental organizations representing the
aviation industry and environmental interests, undertakes ICAO's
technical work in the environmental field. The Committee is responsible
for evaluating, researching, and recommending measures to the ICAO
Council that address the environmental impacts of international civil
aviation. CAEP's terms of reference indicate that ``CAEP's assessments
and proposals are pursued taking into account: technical feasibility;
environmental benefit; economic reasonableness; interdependencies of
measures (for example, among others, measures taken to minimize noise
and emissions); developments in other fields; and international and
national programs.'' \29\ The ICAO Council reviews and adopts the
recommendations made by CAEP. It then reports to the ICAO Assembly, the
highest body of the organization, where the main policies on aviation
environmental protection are adopted and translated into Assembly
Resolutions. If ICAO adopts a CAEP proposal for a new environmental
standard, it then becomes part of ICAO standards and recommended
practices (Annex 16 to the Chicago Convention).30 31
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    \29\ ICAO: CAEP Terms of Reference. A copy of the CAEP Terms of
reference is available in the docket for this rulemaking under
document identification number EPA-HQ-OAR-2019-0660-0006.
    \30\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017. The ICAO Annex 16 Volume
II is found on page 17 of the ICAO Products & Services English
Edition of the 2022 catalog, and it is copyright protected; Order
No. AN16-2. The ICAO Annex 16, Volume II, Fourth Edition, includes
Amendment 10 of January 1, 2021. Amendment 10 is also found on page
17 of this ICAO catalog, and it is copyright protected; Order No. AN
16-2/E/12.
    \31\ CAEP develops new emission standards based on an assessment
of the technical feasibility, cost, and environmental benefit of
potential requirements.
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    The FAA plays an active role in ICAO/CAEP, including serving as the
representative (member) of the United States at annual ICAO/CAEP
Steering Group meetings, as well as the ICAO/CAEP triennial meetings,
and contributing technical expertise to CAEP's working groups. The EPA
serves as an advisor to the U.S. member at the annual ICAO/CAEP
Steering Group and triennial ICAO/CAEP meetings, while also
contributing technical expertise to CAEP's working groups and assisting
and advising the FAA on aviation emissions, technology, and
environmental policy matters. In turn, the FAA assists and advises the
EPA on aviation environmental issues, technology, and airworthiness
certification matters.
    CAEP's predecessor at ICAO, the Committee on Aircraft Engine
Emissions (CAEE), adopted the first international SARPs for aircraft
engine emissions which were proposed in 1981.\32\ These standards
limited aircraft engine emissions of HC, CO, and NOX. The
1981 standards applied to newly manufactured engines, which are those
engines manufactured after the effective date of the regulations--also
referred to as in-production engines. In 1993, ICAO adopted a CAEP/2
proposal to tighten the original NOX standard by 20 percent
and amend the test procedures.\33\ These 1993 standards applied both to
newly certificated turbofan engines (those engine models that received
their initial type certificate after the effective date of the
regulations, also referred to as new type design engines) and to in-
production engines; the standards had different effective dates for
newly certificated engines and in-production engines. In 1995, CAEP/3
recommended a further tightening of the NOX standards by 16
percent and additional test procedure amendments, but in 1997 the ICAO
Council rejected this stringency proposal and approved only the test
procedure amendments. At the CAEP/4 meeting in 1998, the Committee
adopted a similar 16 percent NOX reduction proposal, which
ICAO approved in 1998. Unlike the CAEP/2 standards, the CAEP/4
standards applied only to new type design engines after December 31,
2003, and not to in-production engines, leaving the CAEP/2 standards
applicable to in-production engines. In 2004, CAEP/6 recommended a 12
percent NOX reduction, which ICAO approved in
2005.34 35 The CAEP/6 standards applied to new engine
designs certificated after December 31, 2007, again leaving the CAEP/2
standards in place for in-production engines before January 1, 2013. In
2010, CAEP/8 recommended a further tightening of the NOX
standards by 15 percent for new engine designs certificated after
December 31, 2013.36 37 The Committee also recommended that
the CAEP/6 standards be applied to in-production engines on or after
January 1, 2013, which cut off the production of CAEP/2 and CAEP/4
compliant engines with the exception of spare engines; ICAO adopted
these as standards in 2011.\38\
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    \32\ ICAO, 2017: Aircraft Engine Emissions: Foreword,
International Standards and Recommended Practices, Environmental
Protection, Annex 16, Volume II, Fourth Edition, July 2017. The ICAO
Annex 16, Volume II, Fourth Edition, includes Amendment 10 of
January 1, 2021.
    \33\ CAEP conducts its work triennially. Each 3-year work cycle
is numbered sequentially, and that identifier is used to
differentiate the results from one CAEP meeting to another by
convention. The first technical meeting on aircraft emission
standards was CAEP's predecessor, i.e., CAEE. The first meeting of
CAEP, therefore, is referred to as CAEP/2.
    \34\ CAEP/5 did not address new aircraft engine emission
standards.
    \35\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017. The ICAO Annex 16, Volume
II, Fourth Edition, includes Amendment 10 of January 1, 2021.
    \36\ CAEP/7 did not address new aircraft engine emission
standards.
    \37\ ICAO, 2010: Committee on Aviation Environmental Protection
(CAEP), Report of the Eighth Meeting, Montreal, February 1-12, 2010,
CAEP/8-WP/80. Available in Docket EPA-HQ-OAR-2010-0687.
    \38\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017, Amendment 10. CAEP/8
corresponds to Amendment 7 effective on July 18, 2011. The ICAO
Annex 16, Volume II, Fourth Edition, includes Amendment 10 of
January 1, 2021.
---------------------------------------------------------------------------

    At the CAEP/10 meeting in 2016, the Committee agreed to the first
airplane

carbon dioxide (CO2) emission standards, which ICAO approved
in 2017. The CAEP/10 CO2 standards apply to new type design
airplanes for which the application for a type certificate will be
submitted on or after January 1, 2020, some modified in-production
airplanes on or after January 1, 2023, and all applicable in-production
airplanes manufactured on or after January 1, 2028.
    At the CAEP/10 and CAEP/11 meetings in 2016 and 2019, the Committee
agreed to three different forms of international PM standards for
aircraft engines. Maximum PM mass concentration standards were agreed
to at CAEP/10, and PM mass and number standards were agreed to at CAEP/
11. ICAO adopted the PM maximum mass concentration standards in 2017
and the PM mass and number standards in 2020. The CAEP/10 PM standards
apply to in-production engines on or after January 1, 2020, and the
CAEP/11 PM standards apply to new-type and in-production engines on or
after January 1, 2023. In addition to CAEP/10 agreeing to a maximum PM
mass concentration standard, CAEP/10 adopted a reporting requirement
where aircraft engine manufacturers were required to provide PM mass
concentration, PM mass, and PM number emissions data--and other related
parameters--by January 1, 2020 for in-production engines.\39\
---------------------------------------------------------------------------

    \39\ More specifically, the international PM maximum mass
concentration standard applies to all turbofan and turbojet engines
of a type or model, and their derivative versions, with a rated
output greater than 26.7 kN and whose date of manufacture of the
individual engine is on or after January 1, 2020 (or those engines
manufactured on or after January 1, 2020).
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C. The Relationship Between the EPA's Regulation of Aircraft Engine
Emissions and International Standards

    Domestically, as required by the CAA, the EPA has been engaged in
reducing harmful air pollution from aircraft engines for over 40 years,
regulating gaseous exhaust emissions, smoke, and fuel venting from
engines.\40\ We have periodically revised these regulations.\41\ The
EPA's actions to regulate certain pollutants emitted from aircraft
engines come directly from the authority in CAA section 231, and we
have aligned the U.S. emission requirements with those adopted by ICAO.
As described in Section II.B, the ICAO/CAEP terms of reference includes
technical feasibility.\42\ Technical feasibility has been interpreted
by CAEP as technology demonstrated to be safe and airworthy and
available for application over a sufficient range of newly certificated
aircraft.\43\ This interpretation resulted in all previous ICAO
emission standards, and the EPA's standards reflecting them, being
anti-backsliding standards (i.e., the standards would not reduce
aircraft PM emissions below current engine emission levels), which are
technology-following.
---------------------------------------------------------------------------

    \40\ Emission Standards and Test Procedures for Aircraft; Final
Rule, 38 FR 19088 (July 17, 1973).
    \41\ The following are the most recent EPA rulemakings that
revised these regulations. Control of Air Pollution from Aircraft
and Aircraft Engines; Emission Standards and Test Procedures; Final
Rule, 62 FR 25355 (May 8, 1997); Control of Air Pollution from
Aircraft and Aircraft Engines; Emission Standards and Test
Procedures; Final Rule, 70 FR 69664 (November 17, 2005); Control of
Air Pollution from Aircraft and Aircraft Engines; Emission Standards
and Test Procedures; Final Rule, 77 FR 36342 (June 18, 2012);
Control of Air Pollution From Airplanes and Airplane Engines: GHG
Emission Standards and Test Procedures; Final Rule, 86 FR 2136
(January 11, 2021).
    \42\ ICAO: CAEP Terms of Reference. Available in the docket for
this rulemaking under document identification number EPA-HQ-OAR-
2019-0660-0006.
    \43\ ICAO, 2019: Report of the Eleventh Meeting, Montreal, 4-15
February 2019, Committee on Aviation Environmental Protection,
Document 10126, CAEP/11. It is found on page 27 of the English
Edition of the ICAO Products & Services 2022 Catalog and is
copyright protected: Order No. 10126. The statement on technological
feasibility is located in Appendix C of Agenda Item 3 of this report
(see page 3C-4, paragraph 2.2).
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    For many years the EPA has regulated aircraft engine PM emissions
with smoke number standards.\44\ Since setting the original smoke
number standards in 1973, the EPA has periodically revised these
standards. The EPA amended its smoke standards to align with ICAO's
smoke standards in 1982 \45\ and again in 1984.\46\ Additionally, the
EPA has amended the test procedures for measuring smoke emissions \47\
and modified the effective dates and compliance schedule for smoke
emission standards periodically.\48\ Now, we are adopting three
different forms of aircraft engine PM standards: a PM mass
concentration standard ([mu]g/m\3\), a PM mass standard (mg/kN), and PM
number standard (#/kN). These aircraft engine PM emission standards are
a different way of regulating and/or measuring \49\ aircraft engine PM
emissions in comparison to smoke number emission standards.
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    \44\ See 40 CFR 87.1 (July 1, 2021). ``Smoke means the matter in
exhaust emissions that obscures the transmission of light, as
measured by the test procedures specified in subpart G of this
part.'' ``Smoke number means a dimensionless value quantifying smoke
emission as calculated according to ICAO Annex 16.''
    \45\ Control of Air Pollution From Aircraft and Aircraft
Engines; Emission Standards and Test Procedures, Final Rule, 47 FR
58462 (December 30, 1982).
    \46\ Control of Air Pollution From Aircraft and Aircraft
Engines; Smoke Emission Standard, Final Rule, 49 FR 31873 (August 9,
1984) (bifurcating EPA's smoke standard for new engines into two
regimes--one for engines with rated output less than 26.7
kilonewtons and one for engines with rated output equal to or
greater than 26.7 kilonewtons).
    \47\ 62 FR 25356 (harmonizing EPA procedures with recent
amendments to ICAO test procedures); 70 FR 69664 (same); 77 FR
36342.
    \48\ Amendment to Standards, Final Rule, 43 FR 12614 (March 24,
1978) (setting back by two years the effective date for all gaseous
emission standards for newly manufactured aircraft and aircraft gas
turbine engines); Control of Air Pollution from Aircraft and
Aircraft Engines; Extension of Compliance Date for Emission
Standards Applicable to JT3D Engines, Final Rule, 44 FR 64266
(November 6, 1979) (extending the final compliance date for smoke
emission standards applicable to the JT3D aircraft engines by
roughly 3.5 years); Control of Air Pollution from Aircraft;
Amendment to Standards, Final Rule, 45 FR 86946, (December 31, 1980)
(setting back by two years the effective date for all gaseous
emission standards which would otherwise have been effective on
January 1,1981, for aircraft gas turbine engines); Control of Air
Pollution from Aircraft and Aircraft Engines, Final Rule, 46 FR 2044
(January 8, 1981) (extending the applicability of the temporary
exemption provision of the standards for smoke and fuel venting
emissions from some in-use aircraft engines); Control of Air
Pollution From Aircraft and Aircraft Engines; Smoke Emission
Standard, Final Rule, 48 FR 46481 (October 12, 1983) (staying the
smoke regulations for new turbojet and turbofan engines rated below
26.7 kN thrust).
    \49\ Also, as described in Section IV.D, the final PM standards
employ a different method for measuring aircraft engine PM emissions
compared to the historical smoke number emission standards.
---------------------------------------------------------------------------

    Internationally, the EPA and the FAA have worked within the
standard-setting process of ICAO (CAEP and its predecessor, CAEE) since
the 1970s to help establish international emission standards and
related requirements, which individual member States adopt into
domestic law and regulations. Historically, under this approach,
international emission standards have first been adopted by ICAO, and
subsequently the EPA has initiated rulemakings under CAA section 231 to
establish domestic standards that are harmonized with ICAO's standards.
After the EPA promulgates aircraft engine emission standards, CAA
section 232 requires the FAA to issue regulations to ensure compliance
with the EPA aircraft engine emission standards when certificating
aircraft pursuant to its authority under title 49 of the U.S. Code.
This rulemaking will continue this historical rulemaking approach.
    The EPA and FAA worked from 2009 to 2019 within the ICAO/CAEP
standard-setting process on the development of the three different
forms of international aircraft engine PM emission standards (a PM mass
concentration standard, a PM mass standard, and a PM particle number
standard). In this action, we are adopting PM standards equivalent to
ICAO's three different forms of aircraft engine PM emission standards.
Adoption of these standards will meet

the United States' obligations under the Chicago Convention and will
also help ensure global acceptance of FAA airworthiness certification.
    In December 2018, the EPA issued an information collection request
(ICR) that matches the CAEP/10 PM reporting requirements described in
Section II.B.\50\ In addition to the PM standards, this rulemaking
codifies the reporting requirements implemented by this 2018 EPA ICR
into the EPA regulations, as described in Section IV.E. Also, in a
similar time frame as this rulemaking, the EPA will be renewing this
ICR (the ICR needs to be renewed triennially).
---------------------------------------------------------------------------

    \50\ Information Collection Request Submitted to OMB for Review
and Approval; Comment Request; Aircraft Engines--Supplemental
Information Related to Exhaust Emissions (Renewal), 83 FR 44621
(August 31, 2018). U.S. EPA, Aircraft Engines--Supplemental
Information Related to Exhaust Emissions (Renewal), OMB Control
Number 2060-0680, ICR Reference Number<PHONE_NUMBER>-08, December 17,
2018.
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III. Particulate Matter Impacts on Air Quality and Health

A. Background on Particulate Matter

    Particulate matter (PM) is a highly complex mixture of solid
particles and liquid droplets distributed among numerous atmospheric
gases which interact with solid and liquid phases. Particles range in
size from those smaller than 1 nanometer (10-9 meter) to
over 100 micrometers ([micro]m, or 10-6 meter) in diameter.
For reference, a typical strand of human hair is 70 [mu]m in diameter
and a grain of salt is about 100 [mu]m. Atmospheric particles can be
grouped into several classes according to their aerodynamic and
physical sizes. Generally, the three broad classes of particles include
ultrafine particles (UFPs, generally considered as particulates with a
diameter less than or equal to 0.1 [mu]m (typically based on physical
size, thermal diffusivity or electrical mobility)), ``fine'' particles
(PM2.5; particles with a nominal mean aerodynamic diameter
less than or equal to 2.5 [mu]m), and ``thoracic'' particles
(PM10; particles with a nominal mean aerodynamic diameter
less than or equal to 10 [mu]m). Particles that fall within the size
range between PM2.5 and PM10, are referred to as
``thoracic coarse particles'' (PM10-2.5, particles with a
nominal mean aerodynamic diameter less than or equal to 10 [mu]m and
greater than 2.5 [mu]m).
    Particles span many sizes and shapes and may consist of hundreds of
different chemicals. Particles are emitted directly from sources and
are also formed through atmospheric chemical reactions between PM
precursors; the former are often referred to as ``primary'' particles,
and the latter as ``secondary'' particles. Particle concentration and
composition varies by time of year and location, and, in addition to
differences in source emissions, is affected by several weather-related
factors, such as temperature, clouds, humidity, and wind. Ambient
levels of PM are also impacted by particles' ability to shift between
solid/liquid and gaseous phases, which is influenced by concentration,
meteorology, and especially temperature.
    Fine particles are produced primarily by combustion processes and
by transformations of gaseous emissions (e.g., sulfur oxides
(SOX), NOX and volatile organic compounds (VOCs))
in the atmosphere. The chemical and physical properties of
PM2.5 may vary greatly with time, region, meteorology, and
source category. Thus, PM2.5 may include a complex mixture
of different components including sulfates, nitrates, organic
compounds, elemental carbon, and metal compounds. These particles can
remain in the atmosphere for days to weeks and travel through the
atmosphere hundreds to thousands of kilometers.
    Particulate matter is comprised of both volatile and non-volatile
PM. PM emitted from the engine is known as non-volatile PM (nvPM), and
PM formed from transformation of an engine's gaseous emissions are
defined as volatile PM.\51\ Because of the difficulty in measuring
volatile PM, which is formed in the engine's exhaust plume and is
significantly influenced by ambient conditions, the EPA is adopting
standards only for the emission of nvPM.
---------------------------------------------------------------------------

    \51\ ICAO 2019 Environmental Report. This document is available
in the docket for this rulemaking under document identification
number EPA-HQ-OAR-2019-0660-0022. See pages 98, 100, and 101 for a
description of non-volatile PM and volatile PM.
    ``During the combustion of hydrocarbon-based fuels, aircraft
engines generate gaseous and particulate matter (PM) emissions. At
the engine exhaust, particulate emissions consist mainly of
ultrafine soot or black carbon emissions. These particles, referred
to as ``non-volatile'' PM (nvPM), are present at high temperatures,
in the engine exhaust. Compared to conventional diesel engines, gas
turbine engines emit non-volatile particles of smaller mean
diameter. Their characteristic size ranges roughly from 15 to 60
nanometers. . . . These particles are invisible to the human eye and
are ultrafine.'' (page 98.)
    ``Additionally, gaseous emissions from engines can also condense
to produce new particles (i.e., volatile particulate matter--vPM) or
coat the emitted soot particles. Gaseous emissions species react
chemically with ambient chemical constituents in the atmosphere to
produce the so-called secondary particulate matter. Volatile
particulate matter is dependent on these gaseous precursor
emissions. While these precursors are controlled by gaseous
emissions certification and the fuel composition (e.g., sulfur
content) for aircraft gas turbine engines, the volatile particulate
matter is also dependent on the ambient air background
composition.'' (pages 100 and 101.)
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B. Health Effects of Particulate Matter

    Scientific studies show exposure to ambient PM is associated with a
broad range of health effects. These health effects are discussed in
detail in the U.S. EPA's Integrated Science Assessment for Particulate
Matter (PM ISA), which was finalized in December 2019 (2019 PM ISA),
with a more targeted evaluation of studies published since the
literature cutoff date of the 2019 PM ISA in the Supplement to the
Integrated Science Assessment for PM (Supplement).52 53
Further discussion of PM-related health effects can also be found in
the 2022 Policy Assessment for the review of the PM National Ambient
Air Quality Standards (NAAQS).54 55
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    \52\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \53\ U.S. EPA. Supplement to the 2019 Integrated Science
Assessment for Particulate Matter (Final Report, 2022). U.S.
Environmental Protection Agency, Washington, DC, EPA/600/R-22/028,
2022.
    \54\ U.S. EPA. Policy Assessment for the Reconsideration of the
National Ambient Air Quality Standards for Particulate Matter (Final
Report, 2022). U.S. Environmental Protection Agency, Washington, DC,
EPA-452/R-22-004, 2022.
    \55\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
---------------------------------------------------------------------------

    The 2019 PM ISA concludes that human exposures to ambient
PM2.5 are associated with a number of adverse health effects
and characterizes the weight of evidence for broad health categories
(e.g., cardiovascular effects, respiratory effects, etc.).\56\ The 2019
PM ISA additionally notes that stratified analyses (i.e., analyses that
directly compare PM-related health effects across groups) provide
strong evidence for racial and ethnic differences in PM2.5
exposures and in PM2.5-related health risk. Recent studies
evaluated in the Supplement support the conclusion of the 2019 PM ISA
with respect to disparities in both PM2.5 exposure and
health risk by race and ethnicity and provide additional support for

disparities for lower socioeconomic status populations. As described in
Section III.D, concentrations of PM increase with proximity to an
airport. Further, studies described in Section III.G report that many
communities in close proximity to airports are disproportionately
represented by people of color and low-income populations.
---------------------------------------------------------------------------

    \56\ The causal framework draws upon the assessment and
integration of evidence from across epidemiological, controlled
human exposure, and toxicological studies, and the related
uncertainties that ultimately influence our understanding of the
evidence. This framework employs a five-level hierarchy that
classifies the overall weight of evidence and causality using the
following categorizations: causal relationship, likely to be causal
relationship, suggestive of a causal relationship, inadequate to
infer a causal relationship, and not likely to be a causal
relationship (U.S. EPA. (2009). Integrated Science Assessment for
Particulate Matter (Final Report). U.S. Environmental Protection
Agency, Washington, DC, EPA/600/R-08/139F, Table 1-3).
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    The EPA has concluded that recent evidence in combination with
evidence evaluated in the 2009 PM ISA supports a ``causal
relationship'' between both long- and short-term exposures to
PM2.5 and mortality and cardiovascular effects and a
``likely to be causal relationship'' between long- and short-term
PM2.5 exposures and respiratory effects.\57\ Additionally,
recent experimental and epidemiologic studies provide evidence
supporting a ``likely to be causal relationship'' between long-term
PM2.5 exposure and nervous system effects, and long-term
PM2.5 exposure and cancer. Because of remaining
uncertainties and limitations in the evidence base, the EPA determined
a ``suggestive of, but not sufficient to infer, a causal relationship''
for long-term PM2.5 exposure and reproductive and
developmental effects (i.e., male/female reproduction and fertility;
pregnancy and birth outcomes), long- and short-term exposures and
metabolic effects, and short-term exposure and nervous system effects.
---------------------------------------------------------------------------

    \57\ Short term exposures are usually defined as less than 24
hours duration.
---------------------------------------------------------------------------

    More detailed information on the health effects of PM can be found
in a memorandum to the docket.\58\ The EPA is reconsidering a 2020
decision to retain the PM NAAQS.\59\
---------------------------------------------------------------------------

    \58\ U.S. EPA, Cook, R. Memorandum to Docket EPA-HQ-OAR-2019-
0660, ``Health and environmental effects of non-GHG pollutants
emitted by turbine engine aircraft--final rule version,'' August 11,
2022.
    \59\ Id., p. 6.
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C. Environmental Effects of Particulate Matter

    Environmental effects that can result from particulate matter
emissions include visibility degradation, plant and ecosystem effects,
deposition effects, and materials damage and soiling. These effects are
briefly summarized here and discussed in more detail in the memo to the
docket cited in Section III.B.
    PM2.5 emissions also adversely impact visibility.\60\ In
the Clean Air Act Amendments of 1977, Congress recognized visibility's
value to society by establishing a national goal to protect national
parks and wilderness areas from visibility impairment caused by manmade
pollution.\61\ In 1999, the EPA finalized the regional haze program to
protect the visibility in Mandatory Class I Federal areas.\62\ There
are 156 national parks, forests and wilderness areas categorized as
Mandatory Class I Federal areas.\63\ These areas are defined in CAA
section 162 as those national parks exceeding 6,000 acres, wilderness
areas and memorial parks exceeding 5,000 acres, and all international
parks which were in existence on August 7, 1977. The EPA has also
concluded that PM2.5 causes adverse effects on visibility in
other areas that are not targeted by the Regional Haze Rule, such as
urban areas, depending on PM2.5 concentrations and other
factors such as dry chemical composition and relative humidity (i.e.,
an indicator of the water composition of the particles). The secondary
(welfare-based) PM NAAQS provide protection against visibility effects.
In recent PM NAAQS reviews, EPA evaluated a target level of protection
for visibility impairment that is expected to be met through attainment
of the existing secondary PM standards.\64\
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    \60\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
    \61\ See CAA section 169(a).
    \62\ Regional Haze Regulations; Final Rule, 64 FR 35714 (July 1,
1999).
    \63\ National Ambient Air Quality Standards for Particulate
Matter; Final Rule, 62 FR 38652 (July 18, 1997).
    \64\ Cook, op. cit., p. 6.
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1. Deposition of Metallic and Organic Constituents of PM
    Several significant ecological effects are associated with
deposition of chemical constituents of ambient PM such as metals and
organics.\65\ Like all internal combustion engines, turbine engines
covered by this rule may emit trace amounts of metals due to fuel
contamination or engine wear. Ecological effects of PM include direct
effects to metabolic processes of plant foliage; contribution to total
metal loading resulting in alteration of soil biogeochemistry and
microbiology, plant and animal growth and reproduction; and
contribution to total organics loading resulting in bioaccumulation and
biomagnification.\66\
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    \65\ U.S. EPA. 2018. Integrated Science Assessment (ISA) for
Oxides of Nitrogen, Oxides of Sulfur and Particulate Matter
Ecological Criteria Second External Review Draft). EPA-600-R-18-097.
Washington, DC. December.
    \66\ U.S. EPA. Integrated Science Assessment (ISA) for
Particulate Matter (Final Report, 2019). U.S. Environmental
Protection Agency, Washington, DC, EPA/600/R-19/188, 2019.
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2. Materials Damage and Soiling
    Deposition of PM is associated with both physical damage (materials
damage effects) and impaired aesthetic qualities (soiling effects). Wet
and dry deposition of PM can physically affect materials, adding to the
effects of natural weathering processes, by potentially promoting or
accelerating the corrosion of metals, by degrading paints and by
deteriorating building materials such as stone, concrete and
marble.\67\
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    \67\ U.S. Environmental Protection Agency (U.S. EPA). 2018.
Integrated Science Assessment (ISA) for Oxides of Nitrogen, Oxides
of Sulfur and Particulate Matter Ecological Criteria Second External
Review Draft). EPA-600-R-18-097. Washington, DC. December.
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D. Near-Source Impacts on Air Quality and Public Health

    Airport activity can adversely impact air quality in the vicinity
of airports. Furthermore, these adverse impacts may disproportionately
impact sensitive subpopulations. A recent study by Yim et al (2015)
assessed global, regional, and local health impacts of civil aviation
emissions, using modeling tools that address environmental impacts at
different spatial scales.\68\ The study attributed approximately 16,000
premature deaths per year globally to global aviation emissions, with
87 percent attributable to PM2.5. The study concludes that
about a third of these mortalities are attributable to PM2.5
exposures within 20 kilometers of an airport. Another study focused on
the continental United States estimated 210 deaths per year
attributable to PM2.5 from aircraft activity at
airports.\69\ While there are considerable uncertainties associated
with such estimates, these results suggest that in addition to the
contributions of PM2.5 emissions to regional air quality,
impacts on public health of these emissions in the vicinity of airports
are an important public health concern.
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    \68\ Yim, S.H.L., Lee, G.L., Lee, I.H., Allrogen, F., Ashok, A.,
Caiazzo, F., Eatham, S.D., Malina, R., Barrett, S.R.H. 2015. Global,
regional, and local health impacts of civil aviation emissions.
Environ. Res. Lett. 10: 034001.
    \69\ Brunelle-Yeung, E., Masek, T., Rojo, J., Levy, J.,
Arunachalam, S., Miller, S., Barrett, S., Kuhn, S., Waitz, I. 2014.
Assessing the impact of aviation environmental policies on public
health. Transport Policy 34: 21-28.
---------------------------------------------------------------------------

    A significant body of research has addressed pollutant levels and
potential health effects in the vicinity of airports. Much of this
research was synthesized in a 2015 report published by the Airport
Cooperative Research Program (ACRP), conducted by the Transportation
Research Board.\70\ The

report concluded that PM2.5 concentrations in and around
airports vary considerably, ranging from ``relatively low levels to
those that are close to the NAAQS, and in some cases, exceeding the
standards.'' \71\
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    \70\ Kim, B., Nakada, K., Wayson, R., Christie, S., Paling, C.,
Bennett, M., Raper, D., Raps, V., Levy, J., Roof, C. 2015.
Understanding Airport Air Quality and Public Health Studies Related
to Airports. Airport Cooperative Research Program, ACRP Report 135.
    \71\ Id.
---------------------------------------------------------------------------

    Furthermore, the report states that ``existing studies indicate
that ultrafine particle concentrations are highly elevated at an
airport (i.e., near a runway) with particle counts that can be orders
of magnitude higher than background with some persistence many meters
downwind (e.g., 600 m).'' \72\ Finally, the report concludes that
PM2.5 dominates overall health risks posed by airport
emissions.\73\ Moreover, one recently published study concluded that
emissions from aircraft play an etiologic role in pre-term births,
independent of noise and traffic-related air pollution exposures.\74\
---------------------------------------------------------------------------

    \72\ Id. at 40.
    \73\ Id. at 41.
    \74\ Wing, S.E., Larson, T.V., Hudda, N., Boonyarattaphan, S.,
Fruin, S., Ritz, B. 2020. Preterm birth among infants exposed to in
utero ultrafine particles from aircraft emissions. Environ. Health
Perspect. 128(4).
---------------------------------------------------------------------------

    Since the publication of the 2015 ACRP literature review, a number
of studies conducted in the United States have been published which
concluded that ultrafine particle number concentrations were elevated
downwind of commercial airports, and that proximity to an airport also
increased particle number concentrations within residences. Hudda et
al. investigated ultrafine particle number concentrations (PNC) inside
and outside 16 residences in the Boston metropolitan area. They found
elevated outdoor PNC within several kilometers of the airport. They
also found that aviation-related PNC infiltrated indoors and resulted
in significantly higher indoor PNC.\75\ In another study in the
vicinity of Logan airport, Hudda et al. analyzed PNC impacts of
aviation activities.\76\ They found that, at sites 4.0 and 7.3 km from
the airport, average PNCs were 2 and 1.33-fold higher, respectively,
when winds were from the direction of the airport compared to other
directions, indicating that aviation impacts on PNC extend many
kilometers downwind of Logan airport. Stacey (2019) conducted a
literature survey and concluded that the literature consistently
reports that particle numbers close to airports are significantly
higher than locations distant and upwind of airports, and that the
particle size distribution is different from traditional road traffic,
with more extremely fine particles.\77\ Similar findings have been
published from European studies.78 79 80 81 82 83 Results of
a monitoring study of communities near Seattle-Tacoma International
Airport also found higher levels of ultrafine PM near the airport, and
an impacted area larger than at near-roadway sites.\84\ The PM
associated with aircraft landing activity was also smaller in size,
with lower black carbon concentrations than near-roadway samples. As
discussed in Section III.B, PM2.5 exposures are associated
with a number of serious, adverse health effects. Further, the PM
attributable to aircraft emissions has been associated with potential
adverse health impacts.85 86 For example, He et al. (2018)
found that particle composition, size distribution and internalized
amount of particles near airports all contributed to promotion of
reactive organic species in bronchial epithelial cells.
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    \75\ Hudda, N., Simon, N.C., Zamore, W., Durant, J.L. 2018.
Aviation-related impacts on ultrafine number concentrations outside
and inside residences near an airport. Environ. Sci. Technol. 52:
pp. 1765-1772.
    \76\ Hudda, N., Simon, M.C., Zamore, W., Brugge, D., Durant,
J.L. 2016. Aviation emissions impact ultrafine particle
concentrations in the greater Boston area. Environ. Sci. Technol.
50: pp. 8514-8521.
    \77\ Stacey, B. 2019. Measurement of ultrafine particles at
airports: A review. Atmos. Environ. 198: pp. 463-477.
    \78\ Masiol M., Harrison R.M. Quantification of air quality
impacts of London Heathrow Airport (UK) from 2005 to 2012. Atmos
Environ 2017; 116:308-19.
    \79\ Keuken, M.P., Moerman, M., Zandveld, P., Henzing, J.S.,
Hoek, G., 2015. Total and size-resolved particle number and black
carbon concentrations in urban areas near Schiphol airport (the
Netherlands). Atmos. Environ. 104: pp. 132-142.
    \80\ Pirhadi, M., Mousavi, A., Sowlat, M.H., Janssen, N.A.H.,
Cassee, F.R., Sioutas, C., 2020. Relative contributions of a major
international airport activities and other urban sources to the
particle number concentrations (PNCs) at a nearby monitoring site.
Environ. Pollut, 260: 114027.
    \81\ Stacey, B., Harrison, R.M., Pope, F., 2020. Evaluation of
ultrafine particle concentrations and size distributions at London
Heathrow Airport. Atmos. Environ., 222: 117148.
    \82\ Ungeheuer, F., Pinxteren, D., Vogel, A. 2021.
Identification and source attribution of organic compounds in
ultrafine particles near Frankfurt International Airport. Atmos.
Chem. Phys. 21: pp. 3763-3775.
    \83\ Zhang, X., Karl, M. Zhang, L. Wang, J., 2020. Influence of
Aviation Emission on the Particle Number Concentration near Zurich
Airport. Environ. Sci. Technol. 54: pp. 14161-14171.
    \84\ University of Washington. 2019. Mobile Observations of
Ultrafine Particles: The Mov-UP study report.
    \85\ Habre. R., Zhou, H., Eckel, S., Enebish, T., Fruin, S.,
Bastain, T., Rappaport, E. Gilliland, F. 2018. Short-term effects of
airport-associated ultrafine particle exposure on lung function and
inflammation in adults with asthma. Environment International 118:
pp. 48-59.
    \86\ He, R.-W., Shirmohammadi, F., Gerlofs-Nijland, M.E.,
Sioutas, C., & Cassee, F.R. 2018. Pro-inflammatory responses to PM
(0.25) from airport and urban traffic emissions. The Science of the
total environment, 640-641, pp. 997-100.
---------------------------------------------------------------------------

    Because of these potential impacts, a systematic literature review
was recently conducted to identify peer-reviewed literature on air
quality near commercial airports and assess the quality of the
studies.\87\ The systematic review identified seventy studies for
evaluation. These studies consistently showed that particulate matter,
in the form of UFP, is elevated in and around airports. Furthermore,
many studies showed elevated levels of black carbon, criteria
pollutants, and polycyclic aromatic hydrocarbons as well. Finally, the
systematic review, while not focused on health effects, identified a
limited number of references reporting adverse health effects impacts,
including increased rates of premature death, pre-term births,
decreased lung function, oxidative deoxyribonucleic acid (DNA) damage
and childhood leukemia. As indicated in the proposal, more research is
needed linking particle size distributions to specific airport
activities, and proximity to airports, characterizing relationships
between different pollutants, evaluating long-term impacts, and
improving our understanding of health effects.
---------------------------------------------------------------------------

    \87\ Riley, K., Cook, R., Carr, E., Manning, B. 2021. A
Systematic Review of The Impact of Commercial Aircraft Activity on
Air Quality Near Airports. City and Environment Interactions,
100066.
---------------------------------------------------------------------------

    A systematic review of health effects associated with exposure to
jet engine emissions in the vicinity of airports was also recently
published.\88\ This study concluded that literature on health effects
was sparse, but jet engine emissions have physicochemical properties
similar to diesel exhaust particles, and that exposure to jet engine
emissions is associated with similar adverse health effects as exposure
to diesel exhaust particles and other traffic emissions. A 2010
systematic review by the Health Effects Institute (HEI) concluded that
evidence was sufficient to support a causal relationship between
exposure to traffic-related air pollution and exacerbation of asthma
among children, and suggestive of a causal relationship for childhood
asthma, non-asthma respiratory symptoms, impaired lung function and
cardiovascular mortality.\89\
---------------------------------------------------------------------------

    \88\ Bendtsen, K.M., Bengtsen, E., Saber, A., Vogel, U. 2021. A
review of health effects associated with exposure to jet engine
emissions in and around airports. Environ. Health 20:10.
    \89\ Health Effects institute. ``Special Report 17: A Special
Report of the Institute's Panel on the Health Effects of Traffic-
Related Air Pollution.'' January 2010.

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

E. Contribution of Aircraft Emissions to PM in Selected Areas

    This section provides background on the contribution of aircraft
engine emissions to local PM concentrations. In some areas with large
commercial airports, turbine engine aircraft can make a significant
contribution to ambient PM2.5. To evaluate these potential
impacts, we identified the 25 airports where commercial aircraft
operations are the greatest, based on data for 2017 from the FAA Air
Traffic Data System (ATADS). These 25 commercial airports are located
in 24 counties and 22 metropolitan statistical areas (MSAs). We
compared the contributions of these airports to emissions at both the
county and MSA levels. Comparisons at both scales provide a fuller
picture of how airports are impacting local air quality. Figure III-1
depicts the contribution to county-level PM2.5 direct
emissions from all turbine aircraft in that county with rated output of
greater than 26.7 kN. Emissions data were obtained from the EPA 2017
National Emissions Inventory (NEI).\90\ Inventory estimates for turbine
engine aircraft were adjusted to account for an improved methodology
for estimating PM from nvPM measurements. This adjustment is described
in detail in Section V.B. The contributions of engines greater than
26.7 kN rated output to total turbine engine emissions at individual
airports were estimated based on FAA data.\91\ At the county level,
contributions to total mobile source PM2.5 emissions range
from less than 1 to about 16 percent. However, it should be noted that
two airports cross county lines--Hartsfield-Jackson Atlanta
International Airport (Clayton and Fulton counties) and O'Hare (Cook
and DuPage counties). For those airports, percentages are calculated
for the sum of the two counties. In addition, five of these counties
are in nonattainment for either the PM2.5 or PM10
standard. When emissions from these airports are considered as part of
the entire MSA, the contribution is much smaller. Figure III-2 depicts
the contributions at the metropolitan statistical area (MSA) instead of
the county level, and contributions across airports range from about
0.5 to 3 percent. Details of this analysis are described in a
memorandum to the docket.\92\
---------------------------------------------------------------------------

    \90\ 2017 National Emissions Inventory: Aviation Component,
Eastern Research Group, Inc., June 25, 2020, EPA Contract No. EP-C-
17-011, Work Order No. 2-19. See section 3.2 for airports and
aircraft related emissions in the Technical Supporting Document for
the 2017 National Emissions Inventory, January 2021 Updated Release.
It should be noted that while identification of the 25 airports with
the greatest commercial activity uses 2017 ATADS data, the 2017 NEI
relies on 2014 ATADS data.
    \91\ These data were obtained using radar-informed data from the
FAA Enhanced Traffic Management System (ETMS). The annual fuel burn
and emissions inventories at selected top US airports were based on
the 2015 FAA flight operations database. The fraction of total PM
emissions from aircraft covered by the final PM standards is based
on the ratio of total PM emissions from flights by engines with
thrust rating greater than 26.7 kN compared to PM emissions from the
whole fleet at each airport.
    \92\ U.S. EPA, Cook, R. Memorandum to Docket EPA-HQ-OAR-2019-
0660, ``Estimation of 2017 Emissions Contributions of Turbine
Aircraft >26.7 kN to NOX and PM2.5 as a
Percentage of All Mobile PM2.5 for the Counties and MSAs
in Which the Airport Resides, 25 Largest Carrier Operations--Final
Rule,'' June 14, 2022.
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BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TR23NO22.165

Figure III-1

[GRAPHIC] [TIFF OMITTED] TR23NO22.166

BILLING CODE 6560-50-C
Figure III-2

F. Other Pollutants Emitted by Aircraft

    In addition to particulate matter, a number of other criteria
pollutants are emitted by the aircraft subject to this final rule.
These pollutants, which are not covered by the rule, include
NOX, including nitrogen dioxide (NO2), VOC, CO,
and sulfur dioxide (SO2). Aircraft also contribute to
ambient levels of hazardous air pollutants (HAP), compounds that are
known or suspected human or animal carcinogens, or that have noncancer
health effects. These compounds include, but are not limited to,
benzene, 1,3-butadiene, formaldehyde, acetaldehyde, acrolein,
polycyclic organic matter (POM), and certain metals. Some POM and HAP
metals are components of PM2.5 mass measured in turbine
engine aircraft emissions.\93\
---------------------------------------------------------------------------

    \93\ Kinsey, J.S., Hays, M.D., Dong, Y., Williams, D.C. Logan,
R. 2011. Chemical characterization of the fine particle emissions
from commercial aircraft engines during the aircraft particle
emissions experiment (APEX) 1-3. Environ. Sci. Technol. 45:3415-
3421.
---------------------------------------------------------------------------

    The term polycyclic organic matter (POM) defines a broad class of
compounds that includes the polycyclic aromatic hydrocarbon compounds
(PAHs). POM compounds are formed primarily from combustion and are
present in the atmosphere in gas and particulate form. Metal compounds
emitted from aircraft turbine engine combustion include chromium,
manganese, and nickel. Several POM compounds, as well as hexavalent
chromium, manganese compounds and nickel compounds are included in the
National Air Toxics Assessment, based on potential carcinogenic
risk.\94\ In addition, as mentioned previously, deposition of metallic
compounds can have ecological effects. Impacts of POM and metals are
further discussed in the memorandum to the docket referenced in Section
III.B.
---------------------------------------------------------------------------

    \94\ U.S. EPA, Air Toxics Screening Assessment.
---------------------------------------------------------------------------

G. Environmental Justice

    The EPA's June 2016 ``Technical Guidance for Assessing
Environmental Justice in Regulatory Analysis'' provides recommendations
on conducting the highest quality analysis feasible, recognizing that
data limitations, time and resource constraints, and analytic
challenges will vary by media and regulatory context.\95\ The EPA
defines environmental justice as the fair treatment and meaningful
involvement of all people regardless of race, color, national origin,
or income with respect to the development, implementation, and
enforcement of environmental laws, regulations, and policies.\96\
---------------------------------------------------------------------------

    \95\ ``Technical Guidance for Assessing Environmental Justice in
Regulatory Analysis.'' Environmental Protection Agency (June 2016).
    \96\ Fair treatment means that ``no group of people should bear
a disproportionate burden of environmental harms and risks,
including those resulting from the negative environmental
consequences of industrial, governmental and commercial operations
or programs and policies.'' Meaningful involvement occurs when ``(1)
potentially affected populations have an appropriate opportunity to
participate in decisions about a proposed activity [e.g.,
rulemaking] that will affect their environment and/or health; (2)
the public's contribution can influence [the EPA's rulemaking]
decision; (3) the concerns of all participants involved will be
considered in the decision-making process; and (4) [the EPA will]
seek out and facilitate the involvement of those potentially
affected''. A potential EJ concern is defined as ``the actual or
potential lack of fair treatment or meaningful involvement of
minority populations, low-income populations, tribes, and Indigenous
peoples in the development, implementation and enforcement of
environmental laws, regulations and policies.'' See ``Guidance on
Considering Environmental Justice During the Development of an
Action.'' Environmental Protection Agency.
---------------------------------------------------------------------------

    When assessing the potential for disproportionately high and
adverse health or environmental impacts of regulatory actions on
minority populations, low-income populations, tribes, and/or Indigenous
peoples, the EPA strives to answer three broad questions: (1) Is there
evidence of potential EJ concerns in the baseline (the state of the
world absent the regulatory action)? Assessing the baseline will allow
the EPA to

determine whether pre-existing disparities are associated with the
pollutant(s) under consideration (e.g., if the effects of the
pollutant(s) are more concentrated in some population groups). (2) Is
there evidence of potential EJ concerns for the regulatory option(s)
under consideration? Specifically, how are the pollutant(s) and its
effects distributed for the regulatory options under consideration?
And, (3) do the regulatory option(s) under consideration exacerbate or
mitigate EJ concerns relative to the baseline? It is not always
possible to quantitatively assess these questions.
    The EPA's 2016 Technical Guidance does not prescribe or recommend a
specific approach or methodology for conducting an environmental
justice analysis, though a key consideration is consistency with the
assumptions underlying other parts of the regulatory analysis when
evaluating the baseline and regulatory options. Where applicable and
practicable, the Agency endeavors to conduct such an analysis. Going
forward, the EPA is committed to conducting environmental justice
analysis for rulemakings based on a framework similar to what is
outlined in the EPA's Technical Guidance, in addition to investigating
ways to further weave environmental justice into the fabric of the
rulemaking process.
    Numerous studies have found that environmental hazards such as air
pollution are more prevalent in areas where people of color and low-
income populations represent a higher fraction of the population
compared with the general population, including near transportation
sources.\97\ \98\ \99\ \100\ \101\
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    \97\ Rowangould, G.M. (2013) A census of the near-roadway
population: public health and environmental justice considerations.
Trans Res D 25: pp. 59-67.
    \98\ Marshall, J.D., Swor, K.R., Nguyen, N.P. (2014)
Prioritizing environmental justice and equality: diesel emissions in
Southern California. Environ Sci Technol 48: pp. 4063-4068.
    \99\ Marshall, J.D. (2000) Environmental inequality: air
pollution exposures in California's South Coast Air Basin. Atmos
Environ 21: pp. 5499-5503.
    \100\ Tessum, C.W., Paolella, D.A., Chambliss, SE, Apte, J.S.,
Hill, J.D., Marshall, J.D. (2021) PM2.5 polluters
disproportionately and systemically affect people of color in the
United States. Science Advances 7:eabf4491.
    \101\ Mohai, P., Pellow, D., Roberts Timmons, J. (2009)
Environmental justice. Annual Reviews 34: pp. 405-430.
---------------------------------------------------------------------------

    As described in Section III.D, concentrations of PM increase with
proximity to an airport. Air pollution can disproportionately impact
sensitive subpopulations near airports. Henry et al. (2019) studied
impacts of several California airports on surrounding schools and found
that over 65,000 students spend 1 to 6 hours a day during the academic
year being exposed to airport pollution, and the percentage of impacted
students was higher for those who were economically disadvantaged.\102\
Rissman et al. (2013) studied PM2.5 at the Hartsfield-
Jackson Atlanta International Airport and found that the relationship
between minority population percentages and aircraft-derived PM was
found to grow stronger as concentrations increased.\103\
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    \102\ Henry, R.C., Mohan, S., Yazdani, S. (2019) Estimating
potential air quality impact of airports on children attending the
surrounding schools. Atmospheric Environment, 212: pp. 128-135.
    \103\ Rissman, J., Arunachalam, S., BenDor, T., West, J.J.
(2013) Equity and health impacts of aircraft emissions at the
Hartfield-Jackson Atlanta International Airport, Landscape and Urban
Planning 120: pp. 234-247.
---------------------------------------------------------------------------

    Additional studies have reported that many communities in close
proximity to airports are disproportionately represented by minorities
and low-income populations. McNair (2020) describes nineteen major
airports that underwent capacity expansion projects between 2000 and
2010, thirteen of which met characteristics of race, ethnicity,
nationality and/or income that indicate a disproportionate impact on
these residents.\104\ Woodburn (2017) reports on changes in communities
near airports from 1970-2010, finding suggestive evidence that at many
hub airports over time, the presence of marginalized groups residing in
close proximity to airports increased.\105\
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    \104\ McNair, A. (2020) Investigation of environmental justice
analysis in airport planning practice from 2000 to 2010. Transp.
Research Part D 81:102286.
    \105\ Woodburn, A. (2017) Investigating neighborhood change in
airport-adjacent communities in multiairport regions from 1970 to
2010. Journal of the Transportation Research Board, 2626, pp. 1-8.
---------------------------------------------------------------------------

    Although not being conducted as part of this rulemaking, the EPA is
conducting a demographic analysis to explore whether populations living
nearest the busiest runways show patterns of racial and socioeconomic
disparity.\106\ This will help characterize the state of environmental
justice concerns and inform potential future actions. Finely resolved
population data (i.e., 30 square meters) will be paired with census
block group demographic characteristics to evaluate if people of color,
children, Indigenous populations, and low-income populations are
disproportionately living near airport runways compared to populations
living further away. The results of this analysis could help inform
additional policies to reduce pollution in communities living in close
proximity to airports.
---------------------------------------------------------------------------

    \106\ EPA anticipates that the results of the study will be
released publicly in a separate document from the final rule.
---------------------------------------------------------------------------

    The final in-production standards for both PM mass and PM number
are levels that all aircraft engines in production currently meet to
align with ICAO's standards. Thus, the final standards are not expected
to result in emission reductions, beyond the business-as-usual fleet
turnover that would occur absent the final standards. Therefore, we do
not anticipate an improvement in air quality for those who live near
airports where these aircraft operate, beyond what may occur as a
result of fleet turnover and from any reductions in emissions from
other sectors contributing to air quality near airports.
    Response to comments on Section III of this action can be found in
the Response to Comments document. In addition, all website addresses
for references cited in this section are provided in a memorandum to
the docket.\107\
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    \107\ U.S. EPA, Cook, R. Memorandum to Docket EPA-HQ-OAR-2019-
0660, ``Web addresses for references cited in Section III of the
preamble for Control of Air Pollution from Aircraft Engines:
Emission Standards and Test Procedures; Final Rule,'' November 9,
2022.
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IV. Details of the Final Rule

    In determining what final PM standards are appropriate under CAA
section 231 and after consultation with FAA, the EPA considered the
level of standards that could be met with the application of requisite
technology within the necessary period of time that would allow the
United States to meet its obligations under the Chicago Convention to
at least match the ICAO standards, and gave appropriate consideration
to the cost of compliance within this period. This determination also
took into account the requirement that EPA's revised standards not
significantly increase noise and adversely affect safety. The EPA
considered the statutory requirements in CAA section 231 and other
relevant factors as described in Section VI of both the proposed rule
and this final rule, and we concluded that it was reasonable and
appropriate to finalize the new PM standards that match the
international standards in scope, stringency, and effective date. The
EPA has consulted with FAA and believes sufficient lead time has been
provided since the technology has already been developed and
implemented by manufacturers to comply with the new PM standards. Also,
as described in Section IV.F.1, the EPA is confident that the final
standards will not significantly increase noise and adversely affect

safety. Further, as described in Section VI.D, the EPA does not project
any costs associated with these standards because all in-production
engines meet the in-production standards, nearly all in-production
engines meet the new type design standard, and future new type designs
are expected to meet the new type design standard. In addition to the
statutory requirements of CAA section 231, the EPA, after consultation
with FAA, also took into consideration the importance of controlling PM
emissions, international harmonization of aviation requirements, and
the international nature of the aircraft industry. The EPA gave
significant weight to the United States' treaty obligations under the
Chicago Convention in determining the need for and appropriate levels
of PM standards. U.S. manufacturers could be at a significant
disadvantage if the United States fails to adopt standards by the
international implementation date. Also, given the short timeframe from
this final action and the international implementation date, there
would not be enough lead time for manufacturers to respond to more
stringent standards that would require them to develop and implement
new technologies.
    These considerations led the EPA to determine that adopting
aircraft engine PM standards based on engine standards adopted by ICAO
is appropriate at this time. When developing the PM standards, ICAO
adopted three different methods of measuring the amount of PM emitted.
The first is PM mass, or a measure of the total weight of the particles
produced over the test cycle. This is how the EPA has historically set
PM emission standards for other sectors. The second is PM number, or
the number of particles produced by the engine over the test cycle.
These are two different methods of measuring the same pollutant, PM,
but each provides distinct and valuable information. Third, ICAO
developed PM mass concentration standards, as a replacement to the
existing standards based on smoke number.
    The EPA's final action will apply to subsonic turbofan and turbojet
engines of a type or model with a rated output (maximum thrust
available for takeoff) greater than 26.7 kN, hereinafter referred to as
covered engines, and consists of three key parts: (1) PM mass and
number emission standards for covered engines, (2) a change in test
procedure and form of the existing standards for covered engines--from
smoke number to PM mass concentration, and (3) new testing and
measurement procedures for the PM emission standards and various
updates to the existing gaseous exhaust emissions test procedures.
    Sections IV.A through IV.C describe the final mass, number, and
mass concentration standards for aircraft engines. Section IV.D
describes the test procedures and measurement procedures associated
with the PM standards. Section IV.E presents information related to the
reporting requirements.
    As discussed in Section III.A, PM2.5 consists of both
volatile and non-volatile PM (nvPM), although only non-volatile PM will
be covered by the adopted standards. Only non-volatile PM is present at
the engine exit because the exhaust temperature is too high for
volatile PM to form. The volatile PM (or secondary PM) is formed as the
engine exhaust plume cools and mixes with the ambient air. The result
of this is that the volatile PM is significantly influenced by the
ambient conditions (or ambient air background composition). Because of
this complexity, a test procedure to measure volatile PM has not yet
been developed for aircraft engines. To directly measure non-volatile
PM, ICAO agreed to adopt a measurement procedure, as described in
Section IV.D, which is based on conditions that prevent the formation
of volatile PM upstream of the measurement instruments. The intent of
this approach is to improve the consistency and repeatability of the
non-volatile PM measurement procedure.
    Due to the international nature of the aviation industry, there is
an advantage to working within ICAO to secure the highest practicable
degree of uniformity in international aviation regulations and
standards. Uniformity in international aviation regulations and
standards is a goal of the Chicago Convention, because it ensures that
passengers and the public can expect similar levels of protection for
safety and human health and the environment regardless of manufacturer,
airline, or point of origin of a flight. Further, it helps prevent
barriers in the global aviation market, benefiting both U.S. aircraft
engine manufacturers and consumers.
    When developing new emission standards, ICAO/CAEP seeks to capture
the technological advances made in the control of emissions through the
adoption of anti-backsliding standards reflecting the current state of
technology. The PM standards the EPA is adopting were developed using
this approach. Thus, the adoption of these aircraft engine standards
into U.S. law will simultaneously prevent aircraft engine PM levels
from increasing beyond their current levels, align U.S. domestic
standards with the ICAO standards for international harmonization, meet
the United States' treaty obligations under the Chicago Convention.
    These standards will also allow U.S. manufacturers of covered
aircraft engines to remain competitive in the global marketplace. The
ICAO aircraft engine PM emission standards have been, or are being,
adopted by other ICAO member states that certify aircraft engines. In
the absence of U.S. standards implementing the ICAO aircraft engine PM
emission standards, the United States would not be able to certify
aircraft engines to the PM standards. In this case, U.S. civil aircraft
engine manufacturers could be forced to seek PM emissions certification
from an aviation certification authority of another country to market
and operate their aircraft engines internationally. Foreign
certification authorities may not have the resources to certify
aircraft engines from U.S. manufacturers in a timely manner, which
could lead to delays in these engines being certified. Thus, U.S.
manufacturers could be at a disadvantage if the United States does not
adopt standards that are at least as stringent as the ICAO standards
for PM emissions. This action to adopt, in the United States, PM
standards that match the ICAO standards will help ensure international
consistency and acceptance of U.S.-manufactured engines worldwide.
    The EPA considered whether to propose standards more stringent than
the ICAO standards. See 87 FR 6324, 6337 (February 3, 2022). As noted
in the preceding paragraphs, the EPA, after consultation with FAA,
considered the statutory requirements under CAA section 231, the
importance of controlling PM emissions, international harmonization of
aviation requirements, the international nature of the aircraft
industry and air travel, and the United States' obligations under the
Chicago Convention in evaluating which stringency of standards to
propose. These considerations have historically led the EPA to adopt
international standards developed through ICAO. The EPA concluded that
proposing and now adopting standards equivalent to the ICAO PM
standards in place of more stringent standards is appropriate in part
because international uniformity and regulatory certainty are important
elements of these standards. This is especially true for these final
standards because they change our approach to regulating aircraft PM
emissions from past smoke measurements to the measurement of nvPM mass
concentration, nvPM mass, and nvPM number for the first time. It is

appropriate to gain experience from the implementation of these nvPM
standards before considering whether to adopt more stringent nvPM mass
and/or nvPM number standards, or whether another approach to PM
regulation would better address the health risks of PM emissions from
aircraft engines. Additionally, the U.S. Government, through the FAA,
State Department, and the EPA, played a significant role in the
development of these standards through a multi-year process. The EPA
believes that international cooperation on aircraft emissions brings
substantial benefits overall to the United States. Given that the EPA
and FAA invested significant effort and considerable resources to
develop these standards and obtain international consensus for ICAO to
adopt these standards, a decision by the United States to deviate from
them might well undermine future efforts by the United States to seek
international consensus on aircraft emission standards. For these
reasons, the EPA placed significant weight on international regulatory
uniformity and certainty and is finalizing standards that match the
standards which the EPA worked to develop and adopt at ICAO.

A. PM Mass Standards for Aircraft Engines

1. Applicability of Standards
    These standards for PM mass, like the ICAO standards, will apply to
covered engines whose date of manufacture is on or after January 1,
2023.\108\ These standards will not apply to engines manufactured prior
to this applicability date.
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    \108\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017, III-4-3 & III-4-4pp. The
ICAO Annex 16, Volume II, Fourth Edition, includes Amendment 10 of
January 1, 2021.
    \109\ In most cases, the engine manufacturer applies to the FAA
for the type certification; however, in some cases the applicant may
be different than the manufacturer (e.g., designer).
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    The level of the standard will vary based on when the initial type
certification application is submitted.\109\ Covered engines for which
the type certificate application was first submitted on or after
January 1, 2023 will be subject to the new type level in Section
IV.A.2. These engines are new engines that have not been previously
certificated.
    Covered engines manufactured on or after January 1, 2023 will be
subject to the in-production level, in Section IV.A.3.
2. New Type nvPM Mass Numerical Emission Limits for Aircraft Engines
    Covered engines whose initial type certification application is
submitted to the FAA on or after January 1, 2023 shall not exceed the
level, as defined by Equation IV-1. As described in Section IV.D, the
nvPM mass limit is based on milligram (mg) of PM, as determined over
the LTO cycle, divided by kN of rated output (rO).
[GRAPHIC] [TIFF OMITTED] TR23NO22.167

3. In Production nvPM Mass Numerical Emission Limits for Aircraft
Engines

    Covered engines that are manufactured on or after January 1, 2023
shall not exceed the level, as defined by Equation IV-2.
[GRAPHIC] [TIFF OMITTED] TR23NO22.168

4. Graphical Representation of nvPM Mass Numerical Emission Limits
    Figure IV-1 shows how the nvPM mass emission limits compare to
known in-production engines. Data shown in this figure is from the ICAO
Engine Emissions Databank (EEDB) \110\.
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    \110\ ICAO Aircraft Engine Emissions Databank, July 20, 2021,
``edb-emissions-databank v28C (web).xlsx'', European Union Aviation
Safety Agency (EASA), https://www.easa.europa.eu/domains/environment/icao-aircraft-engine-emissions-databank.
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[GRAPHIC] [TIFF OMITTED] TR23NO22.169

Figure IV-1--nvPM mass standards compared to in-production engine LTO
emission rates

B. PM Number Standards for Aircraft Engines

1. Applicability of Standards
    These standards for PM number, like the ICAO standards, will apply
to covered engines whose date of manufacture is on or after January 1,
2023.\111\ These standards will not apply to engines manufactured prior
to this applicability date.
---------------------------------------------------------------------------

    \111\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017, III-4-4pp. The ICAO Annex
16, Volume II, Fourth Edition, includes Amendment 10 of January 1,
2021.
---------------------------------------------------------------------------

    The level of the standard will vary based on when the initial type
certification application is submitted. Covered engines for which the
type certificate application was first submitted on or after January 1,
2023 will be subject to the new type level in Section IV.B.2. These are
new engines that have not been previously certificated.
    Covered engines manufactured on or after January 1, 2023 will be
subject to the in-production level, in Section IV.B.3.
2. New Type nvPM Number Numerical Emission Limits for Aircraft Engines

    Covered engines whose initial type certification application is
submitted to the FAA on or after January 1, 2023 shall not exceed the
level, as defined by Equation IV-3. As described in Section IV.D, the
nvPM number limit is based on number of particles, as determined over
the LTO cycle, divided by kN of rO.
[GRAPHIC] [TIFF OMITTED] TR23NO22.170

3. In Production nvPM Number Numerical Emission Limits for Aircraft
Engines

    Covered engines that are manufactured on or after January 1, 2023
shall not exceed the level, as defined by Equation IV-4.

[GRAPHIC] [TIFF OMITTED] TR23NO22.171

4. Graphical Representation of nvPM Number Numerical Emission Limits

    Figure IV-2 shows how the nvPM number emission limits compare to
known in-production engines. Data shown in this figure is from the ICAO
Engine Emissions Databank (EEDB).\112\
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    \112\ ICAO Aircraft Engine Emissions Databank, July 20, 2021,
``edb-emissions-databank v28C (web).xlsx,'' European Union Aviation
Safety Agency (EASA).
[GRAPHIC] [TIFF OMITTED] TR23NO22.172

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BILLING CODE 6560-50-C

Figure IV-2--nvPM number standards compared to in-production engine LTO
emission rates

C. PM Mass Concentration Standard for Aircraft Engines

    The previous smoke number-based standards were adopted to reduce
the visible smoke emitted by aircraft engines. Smoke number is
quantified by measuring the opacity of a filter after soot has been
collected upon it during the test procedure. Another means of
quantifying the smoke from an engine exhaust is through PM mass
concentration (PMmc).
    ICAO developed a PM mass concentration standard during the CAEP/10
cycle and adopted it in 2017.\113\ This PM mass concentration standard
was developed to provide equivalent exhaust visibility control as the
existing smoke number standard starting on January 1, 2020. With the
EPA's involvement, the ICAO PM mass concentration limit line was
developed using measured smoke number and PM mass concentration data
from several engines to derive a smoke number-to-PM mass concentration
correlation. This correlation was then used to transform the existing
smoke number-based limit line into a generally equivalent PM mass
concentration limit line, which was ultimately adopted by ICAO as the
CAEP/10 p.m. mass concentration standard. The intention when the
equivalent PM mass concentration standard was adopted was that
equivalent visibility control would be maintained and testing would
coincide with the PM mass and PM number measurement, thus removing the
need to separately test and measure smoke number. In addition to CAEP/
10 agreeing to a maximum PM mass concentration standard, CAEP/10
adopted a reporting requirement where aircraft engine manufacturers
were required to provide PM mass concentration, PM mass, and PM number
emissions data--and other related parameters--by January 1, 2020 for
in-production engines.
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    \113\ ICAO, 2016: Tenth Meeting Committee on Aviation
Environmental Protection Report, Doc 10069, CAEP/10.
---------------------------------------------------------------------------

    While the ICAO PM mass concentration standard was intended to have
equivalent visibility control as the existing smoke number standard,
the method used to derive it was based on limited data and needed to be
confirmed for regulatory purposes. Additional analysis was conducted
during the CAEP/11 cycle to confirm this equivalence. The EPA followed
this work as it progressed, provided input

during the process, and ultimately concurred with the results.\114\ The
analysis, based on aerosol optical theory and visibility criterion,
demonstrated with a high level of confidence that the ICAO PM mass
concentration standard did indeed provide equivalent visibility control
as the existing smoke number standard. This provided the justification
for ICAO to agree to end applicability of the existing smoke number
standard for engines subject to the PM mass concentration standard,
effective January 1, 2023.
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    \114\ ICAO, 2019: Report of Eleventh Meeting, Montreal, 4-15
February 2019, Committee on Aviation Environmental Protection,
Document 10126, CAEP/11. The analysis performed to confirm the
equivalence of the PM mass concentration standard and the SN
standard is located in Appendix C (starting on page 3C-33) of this
report.
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1. PM Mass Concentration Standard
    The EPA is adopting a PM mass concentration standard for all
covered engines manufactured on or after January 1, 2023.\115\ This
standard has the same form, test procedures, and stringency as the
CAEP/10 p.m. mass concentration standard adopted by ICAO in 2017. Note,
the applicability date of the mass concentration standard, finalized in
this action, represents a delay from the January 1, 2020 date agreed to
by ICAO \116\. The PM mass concentration standard is based on the
maximum concentration of PM emitted by the engine at any thrust
setting, measured in micrograms ([micro]g) per meter cubed (m\3\). This
is similar to the previous smoke standard, which is also based on the
measured maximum at any thrust setting. Section IV.D describes the
measurement procedure. Like the LTO-based PM mass and PM number
standards discussed in Section IV.A and Section IV.B (and described in
the introductory paragraphs of Section IV), this is based on the
measurement of nvPM only, not total PM emissions.
---------------------------------------------------------------------------

    \115\ ICAO, 2017: Aircraft Engine Emissions, International
Standards and Recommended Practices, Environmental Protection, Annex
16, Volume II, Fourth Edition, July 2017, III-4-3. The ICAO Annex
16, Volume II, Fourth Edition, includes Amendment 10 of January 1,
2021.
    \116\ A second component of the CAEP/10 agreement was data
collection by January 1, 2020, so the EPA implemented domestically
by updating the Aircraft Engine Emission ICR (EPA ICR Number
2427.04, OMB Control Number 2060-0680) on December 31, 2018 to
include PM emission data.
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    To determine compliance with the PM mass concentration standard,
the maximum nvPM mass concentration [[mu]g/m\3\] will be obtained from
measurements at sufficient thrust settings such that the emission
maximum can be determined. The maximum value will then be converted to
a characteristic level in accordance with the procedures in ICAO Annex
16, Volume II, Appendix 6. The resultant characteristic level must not
exceed the regulatory level determined from the following formula:
[GRAPHIC] [TIFF OMITTED] TR23NO22.178

    Engines certificated under the new PM mass concentration standard
will not need to certify smoke number values and will not be subject to
in-use smoke standards. It is important to note that other smoke number
standards remain in effect for turbofan and turbojet aircraft engines
at or below 26.7 kN rated output and for turboprop engines. Also, the
in-use smoke standards will continue to apply to some already
manufactured aircraft engines that were certified to smoke number
standards. In this final rule, the EPA did not reexamine or reopen the
existing smoke number standards. Any comments we received on the
existing smoke number standards are beyond the scope of this
rulemaking.\117\
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    \117\ The EPA proposed to extend the applicability of the smoke
standards to engines of less than or equal to 26.7 kilonewtons (kN)
rated output used in supersonic airplanes, and so the single comment
received on the extended applicability is within the scope of this
rulemaking and is responded to in the Response to Comments document.
---------------------------------------------------------------------------

2. Graphical Representation of nvPM Mass Concentration Numerical
Emission Limit
    Figure IV-3 shows how the nvPM mass concentration emission limits
compare to known in-production engines, which all were certified to the
previous smoke standard. Data shown in this figure is from the ICAO
Engine Emissions Databank (EEDB).\118\
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    \118\ ICAO Aircraft Engine Emissions Databank, July 20, 2021,
``edb-emissions-databank v28C (web).xlsx,'' European Union Aviation
Safety Agency (EASA).

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[GRAPHIC] [TIFF OMITTED] TR23NO22.173

BILLING CODE 6560-50-C

Figure IV-3--nvPM Mass Concentration Standard

D. Test and Measurement Procedures

1. Aircraft Engine PM Emissions Metrics
    When developing the PM standards, ICAO adopted three different
methods of measuring the amount of PM emitted. The first is PM mass, or
a measure of the total weight of the particles produced over the test
cycle. This is how the EPA has historically measured PM emissions
subject to standards for other sectors. The second is PM number, or the
number of particles produced by the engine over the test cycle. These
are two different methods of measuring the same pollutant, PM, but each
provides valuable information. Third, ICAO developed PM mass
concentration standards, as an alternative to the existing visibility
standards based on smoke.
    The EPA is incorporating by reference the metrics agreed at ICAO
and incorporated into Annex 16 Volume II, to measure PM mass (Equation
IV-6) and PM number (Equation IV-7). These metrics are based on a
measurement of the nvPM emissions, as measured at the instrument, over
the LTO cycle and is normalized by the rated output of the engine (rO).
[GRAPHIC] [TIFF OMITTED] TR23NO22.174

    The EPA is adopting the PM mass concentration standard based on the
maximum mass concentration, in micrograms per meter cubed, produced by
the engine at any thrust setting.
    Regulatory compliance with the emission standards is based on the
product of Equation IV-6 or Equation IV-7 or mass concentration divided
by the appropriate factor from Table IV-2, to obtain the characteristic
level that is used to determine compliance with emission standards (see
Section IV.D.4).
2. Test Procedure
    The EPA is incorporating by reference the PM test and measurement
procedures in ICAO Annex 16, Volume II. These procedures were developed
in conjunction with the Society of Automotive Engineers (SAE) E-31
Aircraft Exhaust Emissions

Measurement Committee \119\ in close consultation between government
and industry, and subsequently they were adopted by ICAO and
incorporated into ICAO Annex 16, Volume II.
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