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

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2022-25134

## Record

- **Collection:** Federal Register
- **Document type:** Rule
- **Published:** November 23, 2022
- **Citation:** 87 FR 72312

## Text

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.

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: (734) 214-4832; email address:
manning.bryan@epa.gov.

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:

Category

NAICS code
a

Examples of potentially affected entities

Industry
336412
Manufacturers of new aircraft engines.

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 (µg/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 (NO
X
), 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 (µg/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.

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).

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.

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.

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.

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.

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 NO
X
emission standards, as well as an integrated standards-setting process to simultaneously update both PM and NO
X
standards for aircraft engines given the strong interdependency between engine NO
X
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.

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 NO
X
, the regulatory limit line is a function of engine overall pressure ratio.

CAEP did not accept the U.S. request to work on updated aircraft engine NO
X
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 CO
2
and noise standards. However, work on an improved NO
X
metric was approved and is underway this CAEP cycle, with an understanding that it is laying the groundwork for a potential update of the NO
X
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.

6
ICAO, 2022: Committee on Aviation Environmental Protection (CAEP), Report of the Twelfth Meeting, Montreal, February 7-17, 2022, Doc 10176, CAEP/12.

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.

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 §§ 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 § 1031.60(a)(5), while the regulatory text solely related to implementing the PM mass and number standards is contained in §§ 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.

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

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).

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

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.

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

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.

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.

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

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

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.

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 NO
X
. 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 NO
X
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 NO
X
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 NO
X
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 NO
X
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 NO
X
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

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 (CO
2
) emission standards, which ICAO approved in 2017. The CAEP/10 CO
2
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).

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).

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 (μg/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.

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 201809-2060-08, December 17, 2018.

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 (µm, or 10
−6
meter) in diameter. For reference, a typical strand of human hair is 70 μm in diameter and a grain of salt is about 100 μm. 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 μm (typically based on physical size, thermal diffusivity or electrical mobility)), “fine” particles (PM
2.5
; particles with a nominal mean aerodynamic diameter less than or equal to 2.5 μm), and “thoracic” particles (PM
10
; particles with a nominal mean aerodynamic diameter less than or equal to 10 μm). Particles that fall within the size range between PM
2.5
and PM
10
, are referred to as “thoracic coarse particles” (PM
10-2.5
, particles with a nominal mean aerodynamic diameter less than or equal to 10 μm and greater than 2.5 μm).

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 (SO
X
), NO
X
and volatile organic compounds (VOCs)) in the atmosphere. The chemical and physical properties of PM
2.5
may vary greatly with time, region, meteorology, and source category. Thus, PM
2.5
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.)

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

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 PM
2.5
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 PM
2.5
exposures and in PM
2.5
-related health risk. Recent studies evaluated in the Supplement support the conclusion of the 2019 PM ISA with respect to disparities in both PM
2.5
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).

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 PM
2.5
and mortality and cardiovascular effects and a “likely to be causal relationship” between long- and short-term PM
2.5
exposures and respiratory effects.
57

Additionally, recent experimental and epidemiologic studies provide evidence supporting a “likely to be causal relationship” between long-term PM
2.5
exposure and nervous system effects, and long-term PM
2.5
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 PM
2.5
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.

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.

PM
2.5
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 PM
2.5
causes adverse effects on visibility in other areas that are not targeted by the Regional Haze Rule, such as urban areas, depending on PM
2.5
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

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.

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

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.

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

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.

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 PM
2.5
. The study concludes that about a third of these mortalities are attributable to PM
2.5
exposures within 20 kilometers of an airport. Another study focused on the continental United States estimated 210 deaths per year attributable to PM
2.5
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 PM
2.5
emissions to regional air quality, impacts on public health of these emissions in the vicinity of airports are an important public health concern.

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 PM
2.5
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

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 PM
2.5
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, PM
2.5
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.

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 PM
2.5
. 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 PM
2.5
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 PM
2.5
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 PM
2.5
or PM
10
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 NO
X
and PM
2.5
as a Percentage of All Mobile PM
2.5
for the Counties and MSAs in Which the Airport Resides, 25 Largest Carrier Operations—Final Rule,” June 14, 2022.

BILLING CODE 6560-50-P

ER23NO22.165

Figure III-1

ER23NO22.166

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 NO
X
, including nitrogen dioxide (NO
2
), VOC, CO, and sulfur dioxide (SO
2
). 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 PM
2.5
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

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) PM
2.5
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 PM
2.5
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

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

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

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.

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, PM
2.5
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.

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).

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).

ER23NO22.167

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.

ER23NO22.168

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
.

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.

BILLING CODE 6560-50-P

ER23NO22.169

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.

ER23NO22.170

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.

ER23NO22.171

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

112
ICAO Aircraft Engine Emissions Databank, July 20, 2021, “edb-emissions-databank v28C (web).xlsx,” European Union Aviation Safety Agency (EASA).

ER23NO22.172

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 (PM
mc
).

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.

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.

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.

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 (µg) 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.

To determine compliance with the PM mass concentration standard, the maximum nvPM mass concentration [μg/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:

ER23NO22.178

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

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

118
ICAO Aircraft Engine Emissions Databank, July 20, 2021, “edb-emissions-databank v28C (web).xlsx,” European Union Aviation Safety Agency (EASA).

ER23NO22.173

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).

ER23NO22.174

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.

119
The E-31 Committee develops and maintains standards for measurement of emissions from aircraft engines. (See
https://www.sae.org/works/committeeHome.do?comtID=TEAE31,
last accessed October 31, 2022).

These procedures build off the existing ICAO Annex 16, Volume II aircraft engine measurement procedures for gaseous pollutants. As described in the Annex 16, at least three engine tests need to be conducted to determine the emissions rates. These tests can be conducted on a single engine or multiple engines.
120

A representative sample of the engine exhaust is sampled at the engine exhaust exit. The exhaust then travels through a heated sample line where it is diluted and kept at a constant temperature prior to reaching the measurement instruments.

120
For example, all three tests could be conducted on a single engine. Or two tests could be conducted on one engine and one test on a second engine. Or three separate engines could each be tested a single time.

The methodology for measuring PM from aircraft engines differs from certain other EPA test procedures for mobile source PM
2.5
standards in two ways. First, as discussed in the introductory paragraphs of Section IV, the procedure is designed to measure only the non-volatile component of PM. The measurement of volatile PM is very dependent on the environment where it is measured. The practical development of a standardized method of measuring volatile PM from aircraft engines has proved challenging. Therefore, the development of a procedure for measuring nvPM was prioritized by ICAO and SAE E-31and the result is adopted in this final rule.

Second, the sample is measured continuously rather than being collected on a filter and measured after the test. This approach was taken primarily for the practical reasons that, due to high dilution rates leading to relatively low concentrations of PM in the sample, collecting enough particulate on a filter to analyze has the potential to take hours. Given the high fuel flow rates of these engines, such lengthy test modes would be very expensive. Additionally, because of the high volume of air required to run a jet engine and the extreme engine exhaust temperatures, it is not possible to collect the full exhaust stream in a controlled manner as is done for other mobile source PM
2.5
measurements.

Included in the procedures now incorporated by reference by the EPA are measurement system specifications and requirements, instrument specifications and calibration requirements, fuel specifications, and corrections for fuel composition, dilution, and thermophoretic losses in the collection part of the sampling system.

To create a uniform sampling system design that works across gas turbine engine testing facilities, the test procedure calls for a 35-meter sample line. This results in a significant portion of the PM being lost in the sample lines, on the order of 50 percent for PM mass and 90 percent for PM number. These particle losses in the sampling system are not corrected for in the standards. Compliance with the standard is based on the measurement at the instruments rather than the exit plane of the engine (instruments are 35 meters from engine exit). This is due to the lack of robustness of the sampling system particle loss correction methodology and that a more stringent standard at the instrument will lead to a reduction in the nvPM emissions at the engine exit plane. A correction methodology has been developed to better estimate the actual PM emitted into the atmosphere. This correction is described in Section V.A.2.

3. Test Duty Cycles

Mass and number PM emissions are measured over the LTO cycle shown in Table IV-1. This is the same duty cycle used to measure gaseous emissions from aircraft engines and is intended to represent operations and flight under an altitude of 3,000 feet near an airport. Emissions rates for each mode can be

[Text truncated at 120,000 characters. The full text is on the page linked above.]

---

Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2022-25134. Public record. Not legal advice.