72372 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

1The FAA regulates ultralight vehicles under 14 

CFR part 103. 

2Rotorcraft encompass helicopters, gyroplanes, 

and any other heavier-than-air aircraft that depend 

principally for support in flight on the lift generated 

by one or more rotors. 

List of Subjects in 33 CFR Part 165 

Harbors, Marine safety, Navigation 

(water), Reporting and recordkeeping 

requirements, Security measures, 

Waterways. 

For the reasons discussed in the 

preamble, the Coast Guard amends 33 

CFR part 165 as follows: 

PART 165—REGULATED NAVIGATION 

AREAS AND LIMITED ACCESS AREAS 

■ 1. The authority citation for part 165 

continues to read as follows: 

Authority: 46 U.S.C. 70034, 70051, 70124; 

33 CFR 1.05–1, 6.04–1, 6.04–6, and 160.5; 

Department of Homeland Security Delegation 

No. 00170.1, Revision No. 01.3. 

■ 2. Add § 165.T08–0797 to read as 

follows: 

§ 165.T08–0797 Safety Zone; Cumberland 

River, Nashville, TN. 

(a) Location. The following area is a 

safety zone: All navigable waters of the 

Cumberland River from Mile Marker 

190 through 191, extending the entire 

width of the river. 

(b) Definitions. As used in this 

section, designated representative 

means a Coast Guard Patrol 

Commander, including a Coast Guard 

coxswain, petty officer, or other officer 

operating a Coast Guard vessel and a 

Federal, State, and local officer 

designated by or assisting the Captain of 

the Port Sector Ohio Valley (COTP) in 

the enforcement of the safety zone. 

(c) Regulations. (1) Under the general 

safety zone regulations in subpart C of 

this part, you may not enter the safety 

zone described in paragraph (a) of this 

section unless authorized by the COTP 

or the COTPs designated representative. 

(2) To seek permission to enter, 

contact the COTP or the COTP’s 

representative by 502–779–5422 or on 

VHR–FM channel 16. Those in the 

safety zone must comply with all lawful 

orders or directions given to them by the 

COTP or the COTP’s designated 

representative. 

(d) Enforcement period. This section 

will be enforced from 7 a.m. through 6 

p.m. daily on October 21, 2023 through 

October 22, 2023. 

Dated: October 16, 2023. 

H.R. Mattern, 

Captain, U.S. Coast Guard, Captain of the 

Port Sector Ohio Valley. 

[FR Doc. 2023–23236 Filed 10–19–23; 8:45 am] 

BILLING CODE 9110–04–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 87, 1031, and 1068 

[EPA–HQ–OAR–2022–0389; FRL–5934–02– 

OAR] 

RIN 2060–AT10 

Finding That Lead Emissions From 

Aircraft Engines That Operate on 

Leaded Fuel Cause or Contribute to Air 

Pollution That May Reasonably Be 

Anticipated To Endanger Public Health 

and Welfare 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final action. 

SUMMARY: In this action, the 

Administrator finds that lead air 

pollution may reasonably be anticipated 

to endanger the public health and 

welfare within the meaning of the Clean 

Air Act. The Administrator also finds 

that engine emissions of lead from 

certain aircraft cause or contribute to the 

lead air pollution that may reasonably 

be anticipated to endanger public health 

and welfare under the Clean Air Act. 

DATES: These findings are effective on 

November 20, 2023. 

ADDRESSES: The EPA has established a 

docket for this action under Docket ID 

No. EPA–HQ–OAR–2022–0389. All 

documents in the docket are listed in 

the https://www.regulations.gov 

website. Publicly available docket 

materials are available either 

electronically in https://

www.regulations.gov or in hard copy at 

the EPA Air and Radiation Docket and 

Information Center, William Jefferson 

Clinton West Building, Room 3334, 

1301 Constitution Ave. NW, 

Washington, DC. The Public Reading 

Room is open from 8:30 a.m. to 4:30 

p.m., Monday through Friday, excluding 

legal holidays. The telephone number 

for the Public Reading Room is (202) 

566–1744, and the telephone number for 

the Air Docket is (202) 566–1742. 

FOR FURTHER INFORMATION CONTACT: Ken 

Davidson, Office of Transportation and 

Air Quality, Assessment and Standards 

Division (ASD), Environmental 

Protection Agency; telephone number: 

(415) 972–3633; email address: 

davidson.ken@epa.gov. 

SUPPLEMENTARY INFORMATION: 

A. General Information 

Does this action apply to me? 

Regulated entities: These final 

findings do not themselves apply new 

requirements to entities other than the 

EPA and the FAA. With respect to 

requirements for the EPA and the FAA, 

as indicated in the proposal for this 

action, if the EPA issues final findings 

that emissions of lead from certain 

classes of engines used in certain 

aircraft cause or contribute to air 

pollution which may reasonably be 

anticipated to endanger public health or 

welfare, the EPA then becomes subject 

to a duty to propose and promulgate 

emission standards pursuant to section 

231 of the Clean Air Act. Upon EPA’s 

issuance of regulations, the FAA shall 

prescribe regulations to ensure 

compliance with the EPA’s emission 

standards pursuant to section 232 of the 

Clean Air Act. In contrast to the 

findings, those future standards would 

apply to and have an effect on other 

entities outside the Federal 

Government. In addition, pursuant to 49 

U.S.C. 44714, the FAA has a statutory 

mandate to prescribe standards for the 

composition or chemical or physical 

properties of an aircraft fuel or fuel 

additive to control or eliminate aircraft 

emissions which the EPA has found 

endanger public health or welfare under 

section 231(a) of the Clean Air Act. In 

issuing these final findings, the EPA is 

making such a finding for emissions of 

lead from engines in covered aircraft. 

The classes of aircraft engines and of 

aircraft relevant to this final action are 

referred to as ‘‘covered aircraft engines’’ 

and as ‘‘covered aircraft,’’ respectively 

throughout this document. Covered 

aircraft engines in this context means 

any aircraft engine that is capable of 

using leaded aviation gasoline. Covered 

aircraft in this context means all aircraft 

and ultralight vehicles 1 equipped with 

covered engines. Covered aircraft 

would, for example, include smaller 

piston-engine aircraft such as the Cessna 

172 (single-engine aircraft) and the 

Beechcraft Baron G58 (twin-engine 

aircraft), as well as the largest pistonengine aircraft such as the Curtiss C–46 

and the Douglas DC–6. Other examples 

of covered aircraft would include 

rotorcraft,2 such as the Robinson R44 

helicopter, light-sport aircraft, and 

ultralight vehicles equipped with piston 

engines. Because the majority of covered 

aircraft are piston-engine powered, this 

document focuses on those aircraft (in 

some contexts the EPA refers to these 

same engines as reciprocating engines). 

All such references and examples used 

in this document are covered aircraft as 

defined in this paragraph. 


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3EPA (2006) A Framework for Assessing Health 

Risks of Environmental Exposures to Children. 

EPA, Washington, DC, EPA/600/R–05/093F, 2006. 

4EPA. Memorandum: Issuance of EPA’s 2021 

Policy on Children’s Health. October 5, 2021. 

Available at https://www.epa.gov/system/files/ 

documents/2021-10/2021-policy-on-childrenshealth.pdf. Children’s environmental health 

includes conception, infancy, early childhood and 

through adolescence until 21 years of age. 

5EPA (2013) ISA for Lead. Executive Summary 

‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– 

lxxxviii. EPA/600/R–10/075F, 2013. See also, 

National Toxicology Program (NTP) (2012) NTP 

Monograph: Health Effects of Low-Level Lead. 

Available at https://ntp.niehs.nih.gov/go/36443. 

6EPA (2013) ISA for Lead. Executive Summary 

‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– 

lxxxviii. EPA/600/R–10/075F, 2013. 

7EPA (2013) ISA for Lead. Section 1.9.4. ‘‘Pb 

Exposure and Neurodevelopmental Deficits in 

Children.’’ p. I–75. EPA/600/R–10/075F, 2013. 

Entities potentially interested in this 

final action include those that 

manufacture and sell covered aircraft 

engines and covered aircraft in the 

United States and those who own or 

operate covered aircraft. Categories that 

may be affected by a future regulatory 

action include, but are not limited to, 

those listed here: 

Category NAICSa code SIC b code Examples of potentially affected entities 

Industry ........................................... 3364412 3724 ................. Manufacturers of new aircraft engines. 

Industry ........................................... 336411 3721 ................. Manufacturers of new aircraft. 

Industry ........................................... 481219 4522 ................. Aircraft charter services (i.e., general purpose aircraft used for a variety of specialty air and flying services). Aviation clubs providing a 

variety of air transportation activities to the general public. 

Industry ........................................... 611512 8249 and 8299 Flight training. 

a North American Industry Classification System (NAICS). 

bStandard Industrial Classification (SIC) code. 

This table is not intended to be 

exhaustive, but rather provides a guide 

for readers regarding entities likely to be 

interested in this final action. This table 

lists examples of the types of entities 

that the EPA is now aware of that could 

potentially have an interest in this final 

action. Other types of entities not listed 

in the table could also be interested and 

potentially affected by subsequent 

actions at some future time. If you have 

any questions regarding the scope of 

this final action, consult the person 

listed in the preceding FOR FURTHER

INFORMATION CONTACT section of this 

document. 

B. Children’s Health 

Children are generally more 

vulnerable to environmental exposures 

and/or the associated health effects, and 

therefore more at risk than adults. These 

risks to children may arise because 

infants and children generally eat more 

food, drink more water and breathe 

more air than adults do, relative to their 

size, and consequently they may be 

exposed to relatively higher amounts of 

contaminants. In addition, normal 

childhood activity, such as putting 

hands in mouths or playing on the 

ground, can result in exposures to 

contaminants that adults do not 

typically have. Furthermore, 

environmental contaminants may pose 

health risks specific to children because 

children’s bodies are still developing. 

For example, during periods of rapid 

growth such as fetal development, 

infancy and puberty, their developing 

systems and organs may be more easily 

harmed.3

Protecting children’s health from 

environmental risks is fundamental to 

the EPA’s mission. This action is subject 

to EPA’s Policy on Children’s Health 

because this action has considerations 

for human health.4 Consistent with this 

policy this document includes 

discussion and analysis that is focused 

particularly on children including early 

life exposure (the lifestages from 

conception, infancy, early childhood 

and through adolescence until 21 years 

of age) and lifelong health. For example, 

as described in section IV. of this 

document, the scientific evidence has 

long been established demonstrating 

that young children (due to rapid 

growth and development of the brain) 

are vulnerable to a range of neurological 

effects resulting from exposure to lead. 

Low levels of lead in young children’s 

blood have been linked to adverse 

effects on intellect, concentration, and 

academic achievement, and as the EPA 

has previously noted ‘‘there is no 

evidence of a threshold below which 

there are no harmful effects on cognition 

from [lead] exposure.’’ 5 Evidence 

suggests that while some neurocognitive 

effects of lead in children may be 

transient, some lead-related cognitive 

effects may be irreversible and persist 

into adulthood, potentially contributing 

to lower educational attainment and 

financial well-being.6 The 2013 Lead 

Integrated Science Assessment notes 

that in epidemiologic studies, postnatal 

(early childhood) blood lead levels are 

consistently associated with cognitive 

function decrements in children and 

adolescents.7 In addition, in section 

II.A.5. of this document, we describe the 

number of children living near and 

attending school near airports and 

provide a proximity analysis of the 

potential for greater representation of 

children in the near-airport 

environment compared with 

neighboring areas. 

Table of Contents 

I. Executive Summary 

II. Overview and Context for This Final 

Action 

A. Background Information Helpful To 

Understanding This Final Action 

1. Piston-Engine Aircraft and the Use of 

Leaded Aviation Gasoline 

2. Emissions of Lead From Piston-Engine 

Aircraft 

3. Concentrations of Lead in Air 

Attributable to Emissions From PistonEngine Aircraft 

4. Fate and Transport of Emissions of Lead 

From Piston-Engine Aircraft 

5. Consideration of Environmental Justice 

and Children in Populations Residing 

Near Airports 

B. Federal Actions To Reduce Lead 

Exposure 

C. Lead Endangerment Petitions for 

Rulemaking and the EPA Responses 

III. Legal Framework for This Action 

A. Statutory Text and Basis for This Action 

B. Considerations for the Endangerment 

and Cause or Contribute Analyses Under 

Section 231(a)(2)(A) 

C. Regulatory Authority for Emission 

Standards 

D. Response to Certain Comments on the 

Legal Framework for This Action 

IV. The Final Endangerment Finding Under 

CAA Section 231 

A. Scientific Basis of the Endangerment 

Finding 

1. Lead Air Pollution 

2. Health Effects and Lead Air Pollution 

3. Welfare Effects and Lead Air Pollution 

B. Final Endangerment Finding 

V. The Final Cause or Contribute Finding 

Under CAA Section 231 

A. Definition of the Air Pollutant 

B. The Data and Information Used To 

Evaluate the Final Cause or Contribute 

Finding 

C. Response to Certain Comments on the 

Cause or Contribute Finding 

D. Final Cause or Contribute Finding for 

Lead 

VI. Statutory Authority and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 


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72374 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

8As noted in section IV.A. of this document, the 

lead air pollution can occur as elemental lead or in 

lead-containing compounds. 

9EPA (2013) ISA for Lead. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

10EPA (2006) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA/600/R–5/144aF, 2006. 

11EPA (1986) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–83/028aF-dF, 1986. 

12EPA (1977) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

13As noted in section V.A. of this document, the 

lead air pollutant can occur as elemental lead or in 

lead-containing compounds. 

14EPA (2022) Proposed Finding that Lead 

Emissions from Aircraft Engines that Operate on 

Leaded Fuel Cause or Contribute to Air Pollution 

that May Reasonably Be Anticipated to Endanger 

Public Health and Welfare 87 FR 62753 (October 17, 

2022). 

15Of these comments, more than 600 were unique 

letters, some of which provided data and other 

information for EPA to consider; the remaining 

comments were mass mailers sponsored by four 

different organizations, all of which urged the EPA 

to take action to finalize the findings and/or to take 

regulatory action to eliminate lead emissions from 

aircraft operating on leaded avgas. 

16U.S. EPA, ‘‘Finding that Lead Emissions from 

Aircraft Engines that Operate on Leaded Fuel Cause 

or Contribute to Air Pollution that May Reasonably 

Be Anticipated to Endanger Public Health and 

Welfare—Response to Comments,’’ Docket EPA– 

HQ–OAR–2022–0389. 

17Under section 108(a)(2) of the CAA, air quality 

criteria are intended to ‘‘accurately reflect the latest 

Order 14094: Modernizing Regulatory 

Review 

B. Paperwork Reduction Act (PRA) 

C. Regulatory Flexibility Act (RFA) 

D. Unfunded Mandates Reform Act 

(UMRA) 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution or Use 

I. National Technology Transfer and 

Advancement Act (NTTAA) 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations; Executive Order 14096: 

Revitalizing Our Nation’s Commitment 

to Environmental Justice for All 

K. Congressional Review Act (CRA) 

L. Determination Under Section 307(d) 

M. Judicial Review 

VII. Statutory Provisions and Legal Authority 

I. Executive Summary 

Pursuant to section 231(a)(2)(A) of the 

Clean Air Act (CAA or Act), the 

Administrator finds that emissions of 

lead from covered aircraft engines cause 

or contribute to lead air pollution that 

may reasonably be anticipated to 

endanger public health and welfare. 

Covered aircraft include, for example, 

smaller piston-engine aircraft such as 

the Cessna 172 (single-engine aircraft) 

and the Beechcraft Baron G58 (twinengine aircraft), as well as the largest 

piston-engine aircraft such as the 

Curtiss C–46 and the Douglas DC–6. 

Other examples of covered aircraft 

include rotorcraft, such as the Robinson 

R44 helicopter, light-sport aircraft, and 

ultralight vehicles equipped with piston 

engines. 

For purposes of this action, the EPA 

defines the ‘‘air pollution’’ referred to in 

section 231(a)(2)(A) of the CAA as lead, 

which we also refer to as the lead air 

pollution in this document.8 In finding 

that the lead air pollution may 

reasonably be anticipated to endanger 

the public health and welfare, the EPA 

relies on the extensive scientific 

evidence critically assessed in the 2013 

Integrated Science Assessment for Lead 

(2013 Lead ISA) and the previous Air 

Quality Criteria Documents (AQCDs) for 

Lead, which the EPA prepared to serve 

as the scientific foundation for periodic 

reviews of the National Ambient Air 

Quality Standards (NAAQS) for 

lead.9 10 11 12

Further, for purposes of this action, 

the EPA defines the ‘‘air pollutant’’ 

referred to in CAA section 231(a)(2)(A) 

as lead, which we also refer to as the 

lead air pollutant in this document.13

Accordingly, the Administrator finds 

that emissions of the lead air pollutant 

from covered aircraft engines cause or 

contribute to the lead air pollution that 

may reasonably be anticipated to 

endanger public health and welfare 

under CAA section 231(a)(2)(A). 

This final action follows the 

Administrator’s proposed findings 14

and includes responses to public 

comments submitted to the EPA on that 

proposal. The proposal was posted on 

the EPA website on October 7, 2022, 

and published in the Federal Register 

on October 17, 2022. The EPA held a 

virtual public hearing on November 1, 

2022, and the public comment period 

closed on January 17, 2023. During the 

public comment period, we received 

more than 53,000 comments.15 The EPA 

received late comments, and to the 

extent feasible we have responded to 

those comments in the Response to 

Comments document for this action. 

A broad range of stakeholders 

provided comments, including state and 

local governments; non-governmental 

organizations; industry trade 

associations representing aircraft engine 

and airframe manufacturers, fuel 

producers, fuel distributors, fuel 

providers, the helicopter industry, and 

aircraft owners and operators; 

environmental organizations; 

environmental justice organizations; one 

Tribe; private citizens; and others. In 

this notice for this final action, we 

summarize and respond to certain 

issues raised by commenters, and we 

provide responses to the remainder of 

comments in the Response to Comments 

document that is available in the public 

docket for this action.16

Section II. of this action includes an 

overview and background information 

that is helpful to understanding the 

source sector in the context of this 

action, a brief summary of some of the 

Federal actions focused on reducing 

lead exposures, and a brief summary of 

the petitions for rulemaking regarding 

lead emissions from aircraft engines. 

Section III. of this document provides 

the legal framework for this action, 

section IV. provides the EPA’s final 

determination on the endangerment 

finding, section V. provides the EPA’s 

final determination on the cause or 

contribute finding, and section VI. 

discusses various statutory authorities 

and executive orders. 

II. Overview and Context for This Final 

Action 

We summarize here background 

information that provides additional 

context for this final action. This 

includes information on the population 

of aircraft that have piston engines, 

information on the use of leaded 

aviation gasoline (avgas) in covered 

aircraft, physical and chemical 

characteristics of lead emissions from 

engines used in covered aircraft, 

concentrations of lead in air from these 

engine emissions, and the fate and 

transport of lead emitted by engines 

used in such aircraft. We also include 

here an analysis of populations residing 

near and attending school near airports 

and an analysis of potential 

environmental justice implications with 

regard to residential proximity to 

runways where covered aircraft operate. 

This section ends with a description of 

a broad range of Federal actions to 

reduce lead exposure from a variety of 

environmental media and a brief 

summary of citizen petitions for 

rulemaking regarding lead emissions 

from covered aircraft and the EPA 

responses. 

A. Background Information Helpful To 

Understanding This Final Action 

This final action draws extensively 

from the EPA’s scientific assessments 

for lead, which are developed as part of 

the EPA’s periodic reviews of the air 

quality criteria 17 for lead and the lead 


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scientific knowledge useful in indicating the kind 

and extent of all identifiable effects on public 

health or welfare which may be expected from the 

presence of [a] pollutant in the ambient air . . . .’’ 

Section 109 of the CAA directs the Administrator 

to propose and promulgate ‘‘primary’’ and 

‘‘secondary’’ NAAQS for pollutants for which air 

quality criteria are issued. Under CAA section 

109(d)(1), EPA must periodically complete a 

thorough review of the air quality criteria and the 

NAAQS and make such revisions as may be 

appropriate in accordance with sections 108 and 

109(b) of the CAA. A fuller description of these 

legislative requirements can be found, for example, 

in the ISA (see 2013 Lead ISA, p. lxix). 

18Section 109(b)(1) defines a primary standard as 

one ‘‘the attainment and maintenance of which in 

the judgment of the Administrator, based on such 

criteria and allowing an adequate margin of safety, 

are requisite to protect the public health.’’ A 

secondary standard, as defined in section 109(b)(2), 

must ‘‘specify a level of air quality the attainment 

and maintenance of which in the judgment of the 

Administrator, based on such criteria, is requisite 

to protect the public welfare from any known or 

anticipated adverse effects associated with the 

presence of [the] pollutant in the ambient air.’’ 

19EPA (2013) ISA for Lead. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

20The EPA released the ISA for Lead External 

Review Draft as part of the Agency’s current review 

of the science regarding health and welfare effects 

of lead. EPA/600/R–23/061. This draft assessment 

is undergoing peer review by the Clean Air 

Scientific Advisory Committee (CASAC) and public 

comment, and is available at: https://cfpub.epa.gov/ 

ncea/isa/recordisplay.cfm?deid=357282. 

21EPA (1977) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

22EPA (1986) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–83/028aF-dF (NTIS 

PB87142386), 1986. 

23EPA (2006) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA/600/R–5/144aF, 2006. 

24EPA (2013) ISA for Lead. Section 3.1.1. 

‘‘Pathways for Pb Exposure.’’ p. 3–1. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

25EPA (2013) ISA for Lead. Section 3.7.1. 

‘‘Exposure.’’ p. 3–144. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

26EPA (2013) ISA for Lead. Section 6.2. ‘‘Fate and 

Transport of Pb in Ecosystems.’’ p. 6–62. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 27EPA (2013) ISA for Lead. Section 2.3. ‘‘Fate and 

Transport of Pb.’’ p. 2–24. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 28EPA (2013) ISA for Lead. Section 1.2.1. 

‘‘Sources, Fate and Transport of Ambient Pb;’’ p. 1– 

6. Section 2.3. ‘‘Fate and Transport of Pb.’’ p. 2–24. 

EPA, Washington, DC, EPA/600/R–10/075F, 2013. 29EPA (2013) ISA for Lead. Section 

3.1.1.’’Pathways for Pb Exposure.’’ p. 3–1. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

30EPA (2013) ISA for Lead. Sections 1.3. 

‘‘Exposure to Ambient Pb.’’ p. 1–11. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

31EPA (2013) ISA for Lead. Sections 3.4.1. ‘‘Pb in 

Blood.’’ p. 3–85; Section 5.4. ‘‘Summary.’’ p. 5–40. 

EPA, Washington, DC, EPA/600/R–10/075F, 2013. 

32EPA (2006) Air Quality Criteria for Lead. 

Chapter 3. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

33EPA (1986) Air Quality Criteria for Lead. 

Section 1.11.3. EPA, Washington, DC, EPA–600/8– 

83/028aF–dF (NTIS PB87142386), 1986. 

34EPA (1977) Air Quality Criteria for Lead. 

Section 12.3.1.1. ‘‘Air Exposures.’’ p. 12–10. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

35EPA (1977) Air Quality Criteria for Lead. 

Section 12.3.1.2. ‘‘Air Exposures.’’ p. 12–10. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

36EPA (1977) Air Quality Criteria for Lead. 

Section 12.3.1.1. ‘‘Air Exposures.’’ p. 12–10. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

37Miranda et al., 2011. A Geospatial Analysis of 

the Effects of Aviation Gasoline on Childhood 

Blood Lead Levels. Environmental Health 

Perspectives. 119:1513–1516. 

38Zahran et al., 2017. The Effect of Leaded 

Aviation Gasoline on Blood Lead in Children. 

Journal of the Association of Environmental and 

Resource Economists. 4(2):575–610. 

39Zahran et al., 2022. Leaded Aviation Gasoline 

Exposure Risk and Child Blood Lead Levels. 

Proceedings of the National Academy of Sciences 

Nexus. 2:1–11. 

40 Klemick et al., 2022. Cardiovascular Mortality 

and Leaded Aviation Fuel: Evidence from PistonEngine Air Traffic in North Carolina. International 

Journal of Environmental Research and Public 

Health. 19(10):5941. 

NAAQS.18 These scientific assessments 

provide a comprehensive review, 

synthesis, and evaluation of the most 

policy-relevant science that builds upon 

the conclusions of previous 

assessments. In the information that 

follows, we discuss and describe 

scientific evidence summarized in the 

most recent assessment for lead, the 

2013 Lead ISA,19 20 as well as 

information summarized in previous 

assessments, including the 1977, 1986, 

and 2006 AQCDs.21 22 23

As described in the 2013 Lead ISA, 

lead emitted to ambient air is 

transported through the air and is 

distributed from air to other 

environmental media through 

deposition.24 Lead emitted in the past 

can remain available for environmental 

or human exposure for an extended time 

in some areas.25 Depending on the 

environment where it is deposited, it 

may to various extents be resuspended 

into the ambient air, integrated into the 

media on which it deposits, or 

transported in surface water runoff to 

other areas or nearby waterbodies.26

Lead in the environment today may 

have been airborne yesterday or emitted 

to the air long ago.27 Over time, lead 

that was initially emitted to air can 

become less available for environmental 

circulation by sequestration in soil, 

sediment and other reservoirs.28

The multimedia distribution of lead 

emitted into ambient air creates 

multiple air-related pathways of human 

and ecosystem exposure. These 

pathways may involve media other than 

air, including indoor and outdoor dust, 

soil, surface water and sediments, 

vegetation and biota. The human 

exposure pathways for lead emitted into 

air include inhalation of ambient air or 

ingestion of food, water or other 

materials, including dust and soil, that 

have been contaminated through a 

pathway involving lead deposition from 

ambient air.29 Ambient air inhalation 

pathways include both inhalation of air 

outdoors and inhalation of ambient air 

that has infiltrated into indoor 

environments.30 The air-related 

ingestion pathways occur as a result of 

lead emissions to air being distributed 

to other environmental media, where 

humans can be exposed to it via contact 

with and ingestion of indoor and 

outdoor dusts, outdoor soil, food and 

drinking water. 

The scientific evidence documents 

exposure to many sources of lead 

emitted to the air that have resulted in 

higher blood lead levels, particularly for 

people living or working near sources, 

including stationary sources, such as 

mines and smelters, and mobile sources, 

such as cars and trucks when lead was 

a gasoline additive.31 32 33 34 35 36

Similarly, with regard to emissions from 

engines used in covered aircraft, there 

have been studies reporting positive 

associations of children’s blood lead 

levels with proximity to airports and 

activity by covered aircraft,37 38 39 thus 

indicating potential for children’s 

exposure to lead from covered aircraft 

engine emissions. A recent study 

evaluating cardiovascular mortality 

rates in adults 65 and older living 

within a few kilometers and downwind 

of runways, while not evaluating blood 

lead levels, found higher mortality rates 

in adults living near single-runway 

airports in years with more pistonengine air traffic, but not in adults living 

near multi-runway airports, suggesting 

the potential for adverse adult health 

effects near some airports.40

1. Piston-Engine Aircraft and the Use of 

Leaded Aviation Gasoline 

Aircraft operating in the U.S. are 

largely powered by either turbine 

engines or piston engines, although 

other propulsion systems are in use and 

in development. Turbine-engine 

powered aircraft and a small percentage 

of piston-engine aircraft (i.e., those with 

diesel engines) operate on fuel that does 

not contain a lead additive. Covered 

aircraft, which are predominantly 

piston-engine powered aircraft, operate 

on leaded avgas. Examples of covered 

aircraft include smaller piston-powered 

aircraft such as the Cessna 172 (singleengine aircraft) and the Beechcraft 

Baron G58 (twin-engine aircraft), as well 

as the largest piston-engine aircraft such 

as the Curtiss C–46 and the Douglas DC– 

6. Additionally, some rotorcraft, such as 

the Robinson R44 helicopter, light-sport 

aircraft, and ultralight vehicles can have 

piston engines that operate using leaded 

avgas. In limited cases, some 

turbopropeller-powered aircraft (also 


ddrumheller on DSK120RN23PROD with RULES1
72376 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

41ASTM International (May 1, 2021) Standard 

Specification for Leaded Aviation Gasolines D910– 

21. 

42National Academies of Sciences, Engineering, 

and Medicine (NAS). 021. Options for Reducing 

Lead Emissions from Piston-Engine Aircraft. 

Washington, DC: The National Academies Press. 

https://doi.org/10.17226/26050. 

43Ogston 1981. A Short History of Aviation 

Gasoline Development, 1903–1980. Society of 

Automotive Engineers. p. 810848. 

44U.S. Department of Commerce Civil 

Aeronautics Administration. Statistical Handbook 

of Aviation (Years 1930–1959). https://

babel.hathitrust.org/cgi/pt?id=mdp.390150

27813032&view=1up&seq=899. 

45U.S. Department of Commerce Civil 

Aeronautics Administration. Statistical Handbook 

of Aviation (Years 1960–1971). https://

babel.hathitrust.org/cgi/pt?id=mdp.39015004

520279&view=1up&seq=9&skin=2021. 

46 DOE. EIA. Petroleum and Other Liquids; 

Supply and Disposition. Aviation Gasoline in 

Annual Thousand Barrels. Fuel production volume 

data obtained from https://www.eia.gov/dnav/pet/ 

pet_sum_snd_a_eppv_mbbl_a_cur-1.htm and 

https://www.eia.gov/dnav/pet/hist/LeafHandler

.ashx?n=PET&s=C400000001&f=A on Dec. 30, 

2021. 

47 Department of Transportation (DOT). FAA. 

Aviation Policy and Plans. FAA Aerospace Forecast 

Fiscal Years 2009–2025. p. 81. Retrieved on Mar. 

22, 2022, from https://www.faa.gov/data_research/ 

aviation/aerospace_forecasts/2009-2025/media/

2009%20Forecast%20Doc.pdf. This document 

provides historical data for 2000–2008 as well as 

forecast data. 

48 DOT. FAA. Aviation Policy and Plans. Table 

23. p. 111. FAA Aerospace Forecast Fiscal Years 

2021–2041. Available at https://www.faa.gov/sites/ 

faa.gov/files/data_research/aviation/aerospace_

forecasts/FY2021-41_FAA_Aerospace_Forecast.pdf. 

49See FAA. NASR. Available at https://

www.faa.gov/air_traffic/flight_info/aeronav/aero_

data/eNASR_Browser/. 

50FAA (2020) National Plan of Integrated Airport 

Systems (NPIAS) 2021–2025 Published by the 

Secretary of Transportation Pursuant to Title 49 

U.S. Code, section 47103. Retrieved on Nov. 3, 2021 

from: https://www.faa.gov/airports/planning_

capacity/npias/current/media/NPIAS-2021-2025- 

Narrative.pdf. 

51See FAA’s NASR. Available at https://

www.faa.gov/air_traffic/flight_info/aeronav/aero_

data/eNASR_Browser/. 

52FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 1: Historical General 

Aviation and Air Taxi Measures. Table 1.1— 

General Aviation and Part 135 Number of Active 

Aircraft By Aircraft Type 2008–2019. Retrieved on 

Dec. 27, 2021 at https://www.faa.gov/data_

research/aviation_data_statistics/general_aviation/ 

CY2019/. Separately, FAA maintains a database of 

FAA registered aircraft and as of January 6, 2022 

there were 222,592 piston engine aircraft registered 

with FAA. See: https://registry.faa.gov/ 

aircraftinquiry/. 

53FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 1: Historical General 

Aviation and Air Taxi Measures. Table 1.1— 

General Aviation and Part 135 Number of Active 

Aircraft By Aircraft Type 2008–2019. Retrieved on 

Dec. 27, 2021 at https://www.faa.gov/data_

research/aviation_data_statistics/general_aviation/ 

CY2019/. 

54 General Aviation Manufacturers Association 

(GAMA) (2019) General Aviation Statistical 

Databook and Industry Outlook, p. 27. Retrieved on 

October 7, 2021 from: https://gama.aero/wpcontent/uploads/GAMA_2019Databook_Final-2020- 

03-20.pdf. 

55 GAMA (2019) General Aviation Statistical 

Databook and Industry Outlook, p. 16. Retrieved on 

October 7, 2021 from: https://gama.aero/wpcontent/uploads/GAMA_2019Databook_Final-2020- 

03-20.pdf. 

56There are both fixed-wing and rotary-wing 

aircraft; and airplane is an engine-driven, fixedwing aircraft and a rotorcraft is an engine-driven 

rotary-wing aircraft. 

57See FAA Aerospace Forecast Fiscal Years 

2021–2041. p. 28. Available at https://www.faa.gov/ 

sites/faa.gov/files/data_research/aviation/ 

aerospace_forecasts/FY2021-41_FAA_Aerospace_

Forecast.pdf. 

58FAA Aerospace Forecast Fiscal Years 2021– 

2041. Table 28. p. 116., and Table 29. p. 117. 

Available at https://www.faa.gov/sites/faa.gov/files/ 

data_research/aviation/aerospace_forecasts/ 

FY2021-41_FAA_Aerospace_Forecast.pdf. 

59FAA. U.S. Civil Airmen Statistics. 2021 Active 

Civil Airman Statistics. Retrieved from https:// 

referred to as turboprops), can use 

leaded avgas. 

Lead is added to avgas in the form of 

tetraethyl lead. Tetraethyl lead helps 

boost fuel octane, prevents engine 

knock, and prevents valve seat recession 

and subsequent loss of compression for 

engines without hardened valves. There 

are three main types of leaded avgas: 

100 Octane, which can contain up to 

4.24 grams of lead per gallon (1.12 

grams of lead per liter), 100 Octane Low 

Lead (100LL), which can contain up to 

2.12 grams of lead per gallon (0.56 

grams of lead per liter), and 100 Octane 

Very Low Lead (100VLL), which can 

contain up to 0.71 grams of lead per 

gallon (0.45 grams of lead per liter).41

Currently, 100LL is the most commonly 

available and most commonly used type 

of avgas.42 Tetraethyl lead was first used 

in piston-engine aircraft in 1927.43

Commercial and military aircraft in the 

U.S. operated on 100 Octane leaded 

avgas into the 1950s, but in subsequent 

years, the commercial and military 

aircraft fleet largely converted to 

turbine-engine powered aircraft which 

do not use leaded avgas.44 45 The use of 

avgas containing approximately 4 grams 

of lead per gallon continued in pistonengine aircraft until the early 1970s 

when 100LL became the dominant 

leaded fuel in use. 

There are two sources of data from the 

Federal Government that provide 

annual estimates of the volume of 

leaded avgas supplied and consumed in 

the U.S.: the Department of Energy, 

Energy Information Administration 

(DOE EIA) provides information on the 

volume of leaded avgas supplied in the 

U.S.,46 and the FAA provides 

information on the volume of leaded 

avgas consumed in the U.S.47 Over the 

ten-year period from 2011 through 2020, 

DOE estimates of the annual volume of 

leaded avgas supplied averaged 184 

million gallons, with year-on-year 

fluctuations in fuel supplied ranging 

from a 25 percent increase to a 29 

percent decrease. Over the same period, 

from 2011 through 2020, the FAA 

estimates of the annual volume of 

leaded avgas consumed averaged 196 

million gallons, with year-on-year 

fluctuations in fuel consumed ranging 

from an eight percent increase to a 14 

percent decrease. The FAA forecast for 

consumption of leaded avgas in the U.S. 

ranges from 185 million gallons in 2026 

to 179 million gallons in 2041, a 

decrease of three percent in that 

period.48 As described later in this 

section, while the national consumption 

of leaded avgas is expected to decrease 

three percent from 2026 to 2041, the 

FAA projects increased activity at some 

airports and decreased activity at other 

airports out to 2045. 

The FAA’s National Airspace System 

Resource (NASR) 49 provides a complete 

list of operational airport facilities in the 

U.S. Among the approximately 19,600 

airports listed in the NASR, 

approximately 3,300 are included in the 

National Plan of Integrated Airport 

Systems (NPIAS) and support the 

majority of piston-engine aircraft 

activity that occurs annually in the 

U.S.50 While less aircraft activity occurs 

at the remaining 16,300 airports, that 

activity is conducted predominantly by 

piston-engine aircraft. Approximately 

6,000 airports have been in operation 

since the early 1970s when the leaded 

fuel being used contained up to 4.24 

grams of lead per gallon of avgas.51 The 

activity by piston-engine aircraft spans 

a range of purposes, as described further 

below. 

As of 2019, there were 171,934 pistonengine aircraft in the U.S.52 This total 

includes 128,926 single-engine aircraft, 

12,470 twin-engine aircraft, and 3,089 

rotorcraft.53 The average age of singleengine aircraft in 2018 was 46.8 years, 

and the average age of twin-engine 

aircraft in 2018 was 44.7 years old.54 In 

2019, 883 new piston-engine aircraft 

were manufactured in the U.S., some of 

which are exported.55 For the period 

from 2019 through 2041, the fleet of 

fixed-wing 56 piston-engine aircraft is 

projected to decrease at an annual 

average rate of 0.9 percent, and the 

hours flown by these aircraft are 

projected to decrease 0.9 percent per 

year from 2019 to 2041.57 An annual 

average growth rate in the production of 

piston-engine powered rotorcraft of 0.9 

percent is forecast, with a 

commensurate 1.9 percent increase in 

hours flown in that period by pistonengine powered rotorcraft.58 There were 

approximately 664,565 pilots certified 

to fly general aviation aircraft in the 

U.S. in 2021.59 This included 197,665 


ddrumheller on DSK120RN23PROD with RULES1
Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 72377 

www.faa.gov/data_research/aviation_data_

statistics/civil_airmen_statistics on May 20, 2022. 

60FAA. U.S. Civil Airmen Statistics. 2021 Active 

Civil Airman Statistics. Retrieved from https://

www.faa.gov/data_research/aviation_data_

statistics/civil_airmen_statistics on May 20, 2022. 

61FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 1: Historical General 

Aviation and Air Taxi Measures. Table 1.4— 

General Aviation and Part 135 Total Hours Flown 

By Actual Use 2008–2019 (Hours in Thousands). 

Retrieved on Dec. 27, 2021 at https://www.faa.gov/ 

data_research/aviation_data_statistics/general_

aviation/CY2019/. 

62FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 3: Primary and Actual 

Use. Table 3.2—General Aviation and Part 135 

Total Hours Flown by Actual Use 2008–2019 

(Hours in Thousands). Retrieved on Mar., 22, 2022 

at https://www.faa.gov/data_research/aviation_

data_statistics/general_aviation/CY2019/. 

63FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 3: Primary and Actual 

Use. Table 5.1—General Aviation and Part 135 

Total Fuel Consumed and Average Fuel 

Consumption Rate by Aircraft Type. Retrieved on 

Feb. 16, 2023 at https://www.faa.gov/data_research/ 

aviation_data_statistics/general_aviation/CY2019/. 

64FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 3: Primary and Actual 

Use. Table 3.2—General Aviation and Part 135 

Total Hours Flown by Actual Use 2008–2019 

(Hours in Thousands). Retrieved on Mar. 22, 2022 

at https://www.faa.gov/data_research/aviation_

data_statistics/general_aviation/CY2019/. 

65FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 3: Primary and Actual 

Use. Table 1.3—General Aviation and Part 135 

Total Hours Flown by Aircraft Type 2008–2019 

(Hours in Thousands). Retrieved on Dec. 27, 2021 

at https://www.faa.gov/data_research/aviation_

data_statistics/general_aviation/CY2019/. 

66 In 2012, the FAA Aerospace Forecast projected 

a 0.03 percent increase in hours flown by the 

piston-engine aircraft fleet for the period 2012 

through 2032. FAA Aerospace Forecast Fiscal Years 

2012–2032. p. 53. Retrieved on Mar. 22, 2022 from 

https://www.faa.gov/data_research/aviation/ 

aerospace_forecasts/media/2012%

20FAA%20Aerospace%20Forecast.pdf. 

67See FAA’s Air Traffic Activity Data. Available 

at https://aspm.faa.gov/opsnet/sys/airport.asp. 

68 Geidosch. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Past Trends and Future 

Projections in General Aviation Activity and 

Emissions. June 1, 2022. Docket ID EPA–HQ–2022– 

0389. 

69FAA’s TAF Fiscal Years 2020–2045 describes 

the forecast method, data sources, and review 

process for the TAF estimates. The documentation 

for the TAF is available at https://taf.faa.gov/ 

Downloads/TAFSummaryFY2020-2045.pdf. 

70The TAF is prepared to assist the FAA in 

meeting its planning, budgeting, and staffing 

requirements. In addition, state aviation authorities 

and other aviation planners use the TAF as a basis 

for planning airport improvements. The TAF is 

available on the internet. The TAF database can be 

accessed at: https://taf.faa.gov. 

student pilots and 466,900 non-student 

pilots. In addition, there were more than 

301,000 FAA Non-Pilot Certificated 

mechanics.60

Piston-engine aircraft are used to 

conduct flights that are categorized as 

either general aviation or air taxi. 

General aviation flights are defined as 

all aviation other than military and 

those flights by scheduled commercial 

airlines. Air taxi flights are short 

duration flights made by small 

commercial aircraft on demand. The 

hours flown by aircraft in the general 

aviation fleet are comprised of personal 

and recreational transportation (67 

percent), business (12 percent), 

instructional flying (8 percent), medical 

transportation (less than one percent), 

and the remainder includes hours spent 

in other applications such as aerial 

observation and aerial application.61

Aerial application for agricultural 

activity includes crop and timber 

production, which involve fertilizer and 

pesticide application and seeding 

cropland. In 2019, aerial application in 

agriculture represented 883,600 hours 

flown by general aviation aircraft, and 

approximately 17.5 percent of these 

total hours were flown by piston-engine 

aircraft.62 While the majority of leaded 

avgas is consumed by piston-engine 

aircraft, in 2019, 403,700 gallons (0.2 

percent) of leaded avgas was consumed 

by turboprop aircraft.63

Approximately 71 percent of the 

hours flown that are categorized as 

general aviation activity are conducted 

by piston-engine aircraft, and 17 percent 

of the hours flown that are categorized 

as air taxi are conducted by pistonengine aircraft.64 From the period 2012 

through 2019, the total hours flown by 

piston-engine aircraft increased nine 

percent from 13.2 million hours in 2012 

to 14.4 million hours in 2019.65 66

As noted earlier, the U.S. has a dense 

network of airports where piston-engine 

aircraft operate, and a small subset of 

those airports have air traffic control 

towers which collect daily counts of 

aircraft operations at the facility (one 

takeoff or landing event is termed an 

‘‘operation’’). These daily operations are 

provided by the FAA in the Air Traffic 

Activity System (ATADS).67 The 

ATADS reports three categories of 

airport operations that can be conducted 

by piston-engine aircraft: Itinerant 

General Aviation, Local Civil, and 

Itinerant Air Taxi. The sum of Itinerant 

General Aviation and Local Civil at a 

facility is referred to as general aviation 

operations. Piston-engine aircraft 

operations in these categories are not 

reported separately from operations 

conducted by aircraft using other 

propulsion systems (e.g., turboprop). 

Because piston-engine aircraft activity 

generally comprises the majority of 

general aviation activity at an airport, 

general aviation activity is often used as 

a surrogate measure for understanding 

piston-engine activity. 

In order to understand the trend in 

airport-specific piston-engine activity in 

the past ten years, we evaluated the 

trend in general aviation activity. We 

calculated the average activity at each of 

the airports in ATADS over three-year 

periods for the years 2010 through 2012 

and for the years 2017 through 2019. We 

focused this trend analysis on the 

airports in ATADS because these data 

are collected daily at an airport-specific 

control tower (in contrast with annual 

activity estimates provided at airports 

without control towers). There were 513 

airports in ATADS for which data were 

available to determine annual average 

activity for both the 2010–2012 period 

and the 2017–2019 time period. The 

annual average operations by general 

aviation at each of these airports in the 

period 2010 through 2012 ranged from 

31 to 346,415, with a median of 34,368; 

the annual average operations by 

general aviation in the period from 2017 

through 2019 ranged from 2,370 to 

396,554, with a median of 34,365. Of the 

513 airports, 211 airports reported 

increased general aviation activity over 

the period evaluated.68 The increase in 

the average annual number of 

operations by general aviation aircraft at 

these 211 facilities ranged from 151 to 

136,872 (an increase of two percent and 

52 percent, respectively). 

While national consumption of leaded 

avgas is forecast to decrease three 

percent from 2026 to 2045, this change 

in fuel consumption is not expected to 

occur uniformly across airports in the 

U.S. The FAA produces the Terminal 

Area Forecast (TAF), which is the 

official forecast of aviation activity for 

the 3,300 U.S. airports that are in the 

NPIAS.69 For the 3,306 airports in the 

TAF, we compared the average activity 

by general aviation at each airport from 

2017–2019 with the FAA forecast for 

general aviation activity at those 

airports in 2045. The FAA forecasts that 

activity by general aviation will 

decrease at 234 of the airports in the 

TAF, remain the same at 1,960 airports, 

and increase at 1,112 of the airports. To 

evaluate the magnitude of potential 

increases in activity for the same 513 

airports for which we evaluated activity 

trends in the past ten years, we 

compared the 2017–2019 average 

general aviation activity at each of these 

airports with the forecasted activity for 

2045 in the TAF.70 The annual 

operations estimated for the 513 airports 

in 2045 ranges from 2,914 to 427,821 

with a median of 36,883. The TAF 

forecasts an increase in activity at 442 

of the 513 airports out to 2045, with the 

increase in operations at those facilities 

ranging from 18 to 83,704 operations 

annually (an increase of 0.2 percent and 

24 percent, respectively). 


ddrumheller on DSK120RN23PROD with RULES1
72378 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

71EPA (1977) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–77–017 (NTIS 

PB280411), 1977. 

72EPA (1986) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–83/028aF–dF (NTIS 

PB87142386), 1986. 

73EPA (2013) ISA for Lead. Section 2.2.2.1 ‘‘Pb 

Emissions from Piston-engine Aircraft Operating on 

Leaded Aviation Gasoline and Other Non-road 

Sources.’’ pp. 2–7 through 2–10. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

74EPA (1986) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA–600/8–83/028aF–dF (NTIS 

PB87142386), 1986. 

75 Griffith 2020. Electron microscopic 

characterization of exhaust particles containing lead 

dibromide beads expelled from aircraft burning 

leaded gasoline. Atmospheric Pollution Research 

11:1481–1486. 

76EPA (1986) Air Quality Criteria for Lead. 

Volume 2: Chapters 5 & 6. EPA, Washington, DC, 

EPA–600/8–83/028aF–dF (NTIS PB87142386), 

1986. 

77EPA (2013) ISA for Lead. Table 2–1. ‘‘Pb 

Compounds Observed in the Environment.’’ p. 2– 

8. EPA, Washington, DC, EPA/600/R–10/075F, 

2013. 

78EPA (2013) ISA for Lead. Section 2.2.2.1 ‘‘Pb 

Emissions from Piston-engine Aircraft Operating on 

Leaded-Aviation Gasoline and Other Non-road 

Sources.’’ p. 2–10. EPA, Washington, DC, EPA/600/ 

R–10/075F, 2013. 

79One commenter asserts that the information 

summarized in the 2013 Lead ISA regarding 

emission of alkyl lead from piston-engine aircraft is 

a supposition and should not inform this action. We 

respond to this comment in the Response to 

Comments document for this action. 

80Memorandum to Docket EPA–HQ–OAR–2022– 

0389. Potential Exposure to Non-exhaust Lead and 

Ethylene Dibromide. June 15, 2022. Docket ID EPA– 

HQ–2022–0389. 

81Swiss FOCA (2007) Aircraft Piston Engine 

Emissions Summary Report. 33–05–003 Piston 

Engine Emissions_Swiss FOCA_Summary. Report_

070612_rit. Available at https://

www.bazl.admin.ch/bazl/en/home/specialists/ 

regulations-and-guidelines/environment/pollutantemissions/aircraft-engine-emissions/report-- 

appendices--database-and-data-sheets.html. 

Retrieved on June 15, 2022. 

82Swiss FOCA (2007) Aircraft Piston Engine 

Emissions Summary Report. 33–05–003 Piston 

Engine Emissions_Swiss FOCA_Summary. Report_

070612_rit. Section 2.2.3.a. Available at https://

www.bazl.admin.ch/bazl/en/home/specialists/ 

regulations-and-guidelines/environment/pollutantemissions/aircraft-engine-emissions/report-- 

appendices--database-and-data-sheets.html. 

Retrieved on June 15, 2022. 

83The lead inventories for 2008, 2011 and 2014 

are provided in the U.S. EPA (2018b) Report on the 

Environment Exhibit 2. Anthropogenic lead 

emissions in the U.S. Available at https://

cfpub.epa.gov/roe/indicator.cfm?i=13#2. 

84EPA 2017 NEI. Available at https://

www.epa.gov/air-emissions-inventories/2017- 

national-emissions-inventory-nei-data. 

2. Emissions of Lead From PistonEngine Aircraft 

This section describes the physical 

and chemical characteristics of lead 

emitted by covered aircraft and the 

national, state, county and airportspecific annual inventories of these 

engine emissions of lead. Information 

regarding lead emissions from motor 

vehicle engines operating on leaded fuel 

is summarized in prior AQCDs for Lead, 

and the 2013 Lead ISA also includes 

information on lead emissions from 

piston-engine aircraft.71 72 73 Lead is 

added to avgas in the form of tetraethyl 

lead along with ethylene dibromide, 

both of which were used in leaded 

gasoline for motor vehicles in the past. 

The piston engines in which leaded fuel 

was used in motor vehicles in the past 

have similarities to piston engines used 

in aircraft including the same 

combustion cycle and the absence of 

aftertreatment devices to limit pollutant 

emissions. Because the same chemical 

form of lead was used in these fuels and 

because of the similarity in the engines 

combusting these leaded fuels, the 

summary of the science regarding 

emissions of lead from motor vehicles 

presented in the 1997 and 1986 AQCDs 

for Lead is relevant to understanding 

some of the properties of lead emitted 

from piston-engine aircraft and the 

atmospheric chemistry these emissions 

are expected to undergo. Recent studies 

relevant to understanding lead 

emissions from piston-engine aircraft 

have also been published and are 

discussed here. 

a. Physical and Chemical Characteristics 

of Lead Emitted by Piston-Engine 

Aircraft 

As with motor vehicle engines, when 

leaded avgas is combusted in aircraft 

engines, the lead is oxidized to form 

lead oxide. In the absence of the 

ethylene dibromide lead scavenger in 

the fuel, lead oxide can collect on the 

valves and spark plugs, and if the 

deposits become thick enough, the 

engine can be damaged. Ethylene 

dibromide reacts with the lead oxide, 

converting it to brominated lead and 

lead oxybromides. These brominated 

forms of lead remain volatile at high 

combustion temperatures and are 

emitted from the engine along with the 

other combustion by-products.74 Upon 

cooling to ambient temperatures these 

brominated lead compounds are 

converted to particulate matter. The 

presence of lead dibromide particles in 

the exhaust from a piston-engine aircraft 

has been confirmed by Griffith (2020) 

and is the primary form of lead emitted 

by engines operating on leaded fuel.75 In 

addition to lead bromides, ammonium 

salts of other lead halides were also 

emitted by motor vehicles, and 

therefore, ammonium salts of lead 

bromide compounds would be expected 

in the exhaust of piston-engine 

aircraft.76

Uncombusted alkyl lead was also 

measured in the exhaust of motor 

vehicles operating on leaded gasoline 

and is therefore likely to be present in 

the exhaust from piston-engine 

aircraft.77 Alkyl lead is the general term 

used for organic lead compounds and 

includes the lead additive tetraethyl 

lead. Summarizing the available data 

regarding emissions of alkyl lead from 

piston-engine aircraft, the 2013 Lead 

ISA notes that lead in the exhaust that 

might be in organic form may 

potentially be 20 percent (as an upper 

bound estimate).78 79 In addition, 

tetraethyl lead is a highly volatile 

compound, and therefore, a portion of 

tetraethyl lead in fuel exposed to air 

will partition into the vapor phase.80

Particles emitted by piston-engine 

aircraft are in the submicron size range 

(less than one micron in diameter). The 

Swiss Federal Office of Civil Aviation 

(FOCA) published a study of pistonengine aircraft emissions including 

measurements of lead.81 The Swiss 

FOCA reported the mean particle 

diameter of particulate matter emitted 

by one single-engine piston-powered 

aircraft operating on leaded fuel that 

ranged from 0.049 to 0.108 microns 

under different power conditions (lead 

particles would be expected to be 

present, but these particles were not 

separately identified in this study). The 

particle number concentration ranged 

from 5.7x106 to 8.6x106 particles per 

cm3. The authors noted that these 

particle emission rates are comparable 

to those from a typical diesel passenger 

car engine without a particle filter.82

Griffith (2020) collected exhaust 

particles from a piston-engine aircraft 

operating on leaded avgas and examined 

the particles using electron microscopy. 

Griffith reported that the mean diameter 

of particles collected in exhaust was 13 

nanometers (0.013 microns) consisting 

of a 4 nanometer (0.004 micron) lead 

dibromide particle surrounded by 

hydrocarbons. 

b. Inventory of Lead Emitted by PistonEngine Aircraft 

Lead emissions from covered aircraft 

are the largest single source of lead to 

air in the U.S., contributing over 50 

percent of lead emissions to air starting 

in 2008 (Table 1).83 In 2017, 

approximately 470 tons of lead were 

emitted by engines in piston-powered 

aircraft, which constituted 70 percent of 

the annual emissions of lead to air in 

that year.84 Lead is emitted at and near 

thousands of airports in the U.S. as 

described in section II.A.1. of this 

document. The EPA’s method for 

developing airport-specific lead 

estimates is described in the EPA’s 

Advance Notice of Proposed 

Rulemaking on Lead Emissions from 

Piston-Engine Aircraft Using Leaded 


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Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 72379 

85Advance Notice of Proposed Rulemaking on 

Lead Emissions from Piston-Engine Aircraft Using 

Leaded Aviation Gasoline. 75 FR 2440 (April 28, 

2010). 

86Airport lead annual emissions data used were 

reported in the 2017 NEI. Available at https://

www.epa.gov/air-emissions-inventories/2017- 

national-emissions-inventory-nei-data. The 

methods used to develop these inventories are 

described in EPA (2010) Calculating Piston-Engine 

Aircraft Airport Inventories for Lead for the 2008 

NEI. EPA, Washington, DC, EPA–420–B–10–044, 

2010. (Also available in the docket for this action, 

EPA–HQ–OAR–2022–0389). 

87The 2017 NEI utilized 2014 aircraft activity 

data to develop airport-specific lead inventories. 

Details can be found on page 3–17 of the document 

located here: https://www.epa.gov/sites/default/ 

files/2021-02/documents/nei2017_tsd_full_

jan2021.pdf#page=70&zoom=100,68,633. Because 

the 2020 inventory was impacted by the Covid–19 

pandemic-related decrease in activity by aircraft in 

2020, the EPA is focusing on the 2017 inventory in 

this final action. 

88Lead emitted in-flight is assigned to states 

based on their overall fraction of total piston-engine 

aircraft operations. The state-level estimates of 

engine emissions of lead include both lead emitted 

in the landing and takeoff cycle as well as lead 

emitted in-flight. The method used to develop these 

estimates is described in EPA (2010) Calculating 

Piston-Engine Aircraft Airport Inventories for Lead 

for the 2008 NEI, available here: https://

nepis.epa.gov/Exe/ZyPDF.cgi/P1009I13.PDF?

Dockey=P1009I13.PDF. 

89Airport lead annual emissions data cited were 

reported in the 2017 NEI. Available at https://

www.epa.gov/air-emissions-inventories/2017- 

national-emissions-inventory-nei-data. In addition 

to the triennial NEI, the EPA collects from state, 

local, and Tribal air agencies point source data for 

larger sources every year (see https://www.epa.gov/ 

air-emissions-inventories/air-emissions-reportingrequirements-aerr for specific emissions 

thresholds). While these data are not typically 

published as a new NEI, they are available publicly 

upon request and are also included in https://

www.epa.gov/air-emissions-modeling/emissionsmodeling-platforms that are created for years other 

than the triennial NEI years. County estimates of 

lead emissions from non-aircraft sources used in 

this action are from the 2019 inventory. There are 

3,012 counties and statistical equivalent areas 

where EPA estimates engine emissions of lead 

occur. 

90See EPA lead inventory data available at 

https://www.epa.gov/air-emissions-modeling/ 

emissions-modeling-platforms. 

91EPA used the method described in EPA (2010) 

Calculating Piston-Engine Aircraft Airport 

Inventories for Lead for the 2008 NEI to estimate 

airport lead inventories in 2045. This document is 

available here: https://nepis.epa.gov/Exe/ZyPDF

.cgi/P1009I13.PDF?Dockey=P1009I13.PDF. 

92 Geidosch. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Lead Emissions from the use of 

Leaded Aviation Gasoline from 1930 through 2020. 

June 1, 2022. Docket ID EPA–HQ–2022–0389. 

Aviation Gasoline 85 and in the 

document titled ‘‘Calculating PistonEngine Aircraft Airport Inventories for 

Lead for the 2008 National Emissions 

Inventory.’’ 86 The EPA’s National 

Emissions Inventory (NEI) reports 

airport estimates of lead emissions as 

well as estimates of lead emitted inflight, which are allocated to states 

based on the fraction of piston-engine 

aircraft activity estimated for each state. 

These inventory data are briefly 

summarized here at the state, county, 

and airport level.87

TABLE 1—PISTON-ENGINE EMISSIONS OF LEAD TO AIR

2008 2011 2014 2017 2020 a

Piston-engine emissions of lead to air, tons ........................................... 560 490 460 470 427 

Total U.S. lead emissions, tons ............................................................... 950 810 720 670 621 

Piston-engine emissions as a percent of the total U.S. lead inventory .. 59% 60% 64% 70% 69% 

a Due to the Covid-19 Pandemic, a substantial decrease in activity by aircraft occurred in 2020, impacting the total lead emissions for this year. 

The 2020 NEI is available at: https://www.epa.gov/air-emissions-inventories/2020-national-emissions-inventory-nei-data. 

At the state level, the EPA estimates 

of lead emissions from piston-engine 

aircraft range from 0.3 tons (Rhode 

Island) to 50.5 tons (California), 47 

percent of which is emitted in the 

landing and takeoff cycle and 53 percent 

of which the EPA estimates is emitted 

in-flight, outside the landing and takeoff 

cycle.88 Among the counties in the U.S. 

where the EPA estimates engine 

emissions of lead from covered aircraft, 

these lead inventories range from 

0.00005 tons per year to 4.3 tons per 

year and constitute the only source of 

air-related lead in 1,140 counties (the 

county estimates of lead emissions 

include the lead emitted during the 

landing and takeoff cycle and not lead 

emitted in-flight).89 In the counties 

where engine emissions of lead from 

aircraft are the sole source of lead to 

these estimates, annual lead emissions 

from the landing and takeoff cycle 

ranged from 0.00015 to 0.74 tons. 

Among the 1,872 counties in the U.S. 

with multiple sources of lead, including 

engine emissions from covered aircraft, 

the contribution of aircraft engine 

emissions ranges from 0.00005 to 4.3 

tons, comprising 0.15 to 98 percent of 

the county total, respectively. 

The EPA estimates that among the 

approximately 20,000 airports in the 

U.S., airport lead inventories range from 

0.00005 tons per year to 0.9 tons per 

year.90 In 2017, the EPA’s NEI includes 

638 airports where the EPA estimates 

engine emissions of lead from covered 

aircraft were 0.1 ton or more of lead 

annually. Using the FAA’s forecasted 

activity in 2045 for the approximately 

3,300 airports in the NPIAS (as 

described in section II.A.1. of this 

document), the EPA estimates airportspecific inventories may range from 

0.00003 tons to 1.28 tons of lead 

(median of 0.03 tons), with 656 airports 

estimated to have inventories above 0.1 

tons in 2045.91

We estimate that piston-engine 

aircraft have consumed approximately 

38.6 billion gallons of leaded avgas in 

the U.S. since 1930, excluding military 

aircraft use of this fuel, emitting 

approximately 113,000 tons of lead to 

the air.92

3. Concentrations of Lead in Air 

Attributable to Emissions From PistonEngine Aircraft 

In this section, we describe the 

concentrations of lead in air resulting 

from emissions of lead from covered 

aircraft. Air quality monitoring and 

modeling studies for lead at and near 

airports have identified elevated 


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72380 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

93Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment, 45 (32), 5795–5804. 

DOI: https://dx.doi.org/10.1016/ 

j.atmosenv.2011.07.017. 

94Feinberg et al., 2016. Modeling of Lead 

Concentrations and Hot Spots at General Aviation 

Airports. Journal of the Transportation Research 

Board, No. 2569, Transportation Research Board, 

Washington, DC, pp. 80–87. DOI: 10.3141/2569–09. 

95Municipality of Anchorage (2012). Merrill Field 

Lead Monitoring Report. Municipality of Anchorage 

Department of Health and Human Services. 

Anchorage, Alaska. Available at https://

www.muni.org/Departments/health/Admin/ 

environment/AirQ/Documents/ 

Merrill%20Field%20Lead%20Monitoring%20

Study_2012/Merrill%20Field%20

Lead%20Study%20Report%20-%20final.pdf. 

96Environment Canada (2000) Airborne 

Particulate Matter, Lead and Manganese at 

Buttonville Airport. Toronto, Ontario, Canada: 

Conor Pacific Environmental Technologies for 

Environmental Protection Service, Ontario Region. 

97Fine et al., 2010. General Aviation Airport Air 

Monitoring Study. South Coast Air Quality 

Management District. Available at https://

www.aqmd.gov/docs/default-source/air-quality/airquality-monitoring-studies/general-aviation-study/ 

study-of-air-toxins-near-van-nuys-and-santamonica-airport.pdf. 

98Lead emitted from piston-engine aircraft in the 

particulate phase would also be measured in 

samples collected to evaluate total ambient PM2.5

concentrations. 

99One commenter provided results from a 

monitoring and modeling study at a general 

aviation airport in Wisconsin that reports increased 

lead concentrations with increasing proximity to 

the airport. See attachments provided to the 

comments from the Town of Middleton (EPA–HQ– 

OAR–2022–0389–0178_attachment_2.pdf and EPA– 

HQ–OAR–2022–0389–0178_attachment_3.pdf) 

available in the docket for this action EPA–HQ–

OAR–2022–0389. 

100EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?

Dockey=P100YG52.pdf. EPA responses to peer 

review comments on the report are available at 

https://nepis.epa.gov/Exe/ZyPDF.cgi?

Dockey=P100YIWD.pdf. These documents are also 

available in the docket for this action (Docket EPA– 

HQ–OAR–2022–0389). 

101EPA (2022) Technical Support Document 

(TSD) for the EPA’s Proposed Finding that Lead 

Emissions from Aircraft Engines that Operate on 

Leaded Fuel Cause or Contribute to Air Pollution 

that May Reasonably Be Anticipated to Endanger 

Public Health and Welfare. EPA, Washington, DC, 

EPA–420–R–22–025, 2022. Available in the docket 

for this action. 102Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment, 45 (32), 5795–5804. 

DOI: https://dx.doi.org/10.1016/j.atmosenv.

2011.07.017. 103Heiken et al., 2014. Quantifying Aircraft Lead 

Emissions at Airports. ACRP Report 133. Available 

at https://www.nap.edu/catalog/22142/quantifyingaircraft-lead-emissions-at-airports. 104Hudda et al., 2022. Substantial Near-Field Air 

Quality Improvements at a General Aviation Airport 

Following a Runway Shortening. Environmental 

Science & Technology. DOI: 10.1021/ 

acs.est.1c06765. 105Fine et al., 2010. General Aviation Airport Air 

Monitoring Study. South Coast Air Quality 

Management District. Available at https://

www.aqmd.gov/docs/default-source/air-quality/airquality-monitoring-studies/general-aviation-study/ 

study-of-air-toxins-near-van-nuys-and-santamonica-airport.pdf. 

106EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

107EPA (2010) Development and Evaluation of an 

Air Quality Modeling Approach for Lead Emissions 

from Piston-Engine Aircraft Operating on Leaded 

Aviation Gasoline. EPA, Washington, DC, EPA– 

420–R–10–007, 2010. https://nepis.epa.gov/Exe/ 

ZyPDF.cgi/P1007H4Q.PDF?

Dockey=P1007H4Q.PDF. 

108EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

109Feinberg et al., 2016. Modeling of Lead 

Concentrations and Hot Spots at General Aviation 

Airports. Journal of the Transportation Research 

Board, No. 2569, Transportation Research Board, 

Washington, DC, pp. 80–87. DOI: 10.3141/2569–09. 

110Feinberg et al., 2016. Modeling of Lead 

Concentrations and Hot Spots at General Aviation 

Airports. Journal of the Transportation Research 

Board, No. 2569, Transportation Research Board, 

Washington, DC, pp. 80–87. DOI: 10.3141/2569–09. 

111 73 FR 66965 (Nov. 12, 2008). 

112 40 CFR 50.16 (Nov. 12, 2008). 

113 75 FR 81126 (Dec. 27, 2010). 

concentrations of lead in air from 

piston-engine aircraft exhaust at, and 

downwind of, airports where these 

aircraft are active.93 94 95 96 97 98 99 This 

section provides a summary of the 

literature regarding the local-scale 

impact of aircraft emissions of lead on 

concentrations of lead at and near 

airports, with specific focus on the 

results of air monitoring for lead that the 

EPA required at a subset of airports and 

an analysis conducted by the EPA to 

estimate concentrations of lead at 

13,000 airports in the U.S., titled 

‘‘Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. 

Airports.’’ 100 101

Gradient studies evaluate how lead 

concentrations change with distance 

from an airport where piston-engine 

aircraft operate. These studies indicate 

that concentrations of lead in air, 

averaged over periods of 18 hours to 

three months, are estimated to be one to 

two orders of magnitude higher at 

locations proximate to aircraft 

emissions, compared to nearby locations 

not impacted by a source of lead air 

emissions.102 103 104 105 106 The magnitude 

of lead concentrations at and near 

airports is highly influenced by the 

amount of aircraft activity (i.e., the 

number of take-off and landing 

operations, particularly if concentrated 

at one runway) and the time spent by 

aircraft in specific modes of operation. 

The most significant emissions in terms 

of ground-based activity, and therefore 

ground-level concentrations of lead in 

air, occur near the areas with greatest 

fuel consumption where the aircraft are 

stationary and running.107 108 109 For 

piston-engine aircraft these areas are 

most commonly locations in which 

pilots conduct engine tests during runup operations prior to take-off (e.g., 

magneto checks during the run-up 

operation mode). Run-up operations are 

conducted while the brakes are engaged 

so the aircraft is stationary and are often 

conducted adjacent to the runway end 

from which the aircraft will take off. 

Additional modes of operation by 

piston-engine aircraft, such as taxiing or 

idling near the runway, may result in 

additional hotspots of elevated lead 

concentration (e.g., start-up and idle, 

maintenance run-up).110

The lead NAAQS was revised in 

2008.111 The 2008 decision revised the 

level, averaging time and form of the 

standards to establish the current 

primary and secondary standards, 

which are both 0.15 micrograms per 

cubic meter of air, in terms of the 

average of three consecutive monthly 

averages of lead in total suspended 

particles within a three-year period.112

In conjunction with strengthening the 

lead NAAQS in 2008, the EPA enhanced 

the existing lead monitoring network by 

requiring monitors to be placed in areas 

with sources such as industrial facilities 

and airports with estimated lead 

emissions of 1.0 ton or more per year. 

Lead monitoring was conducted at two 

airports following from these 

requirements (Deer Valley Airport, AZ, 

and the Van Nuys Airport, CA). In 2010, 

the EPA made further revisions to the 

monitoring requirements such that state 

and local air quality agencies are 

required to monitor near industrial 

facilities with estimated lead emissions 

of 0.50 tons or more per year and at 

airports with estimated emissions of 1.0 

ton or more per year.113 As part of this 

2010 requirement to expand lead 

monitoring, the EPA also required a 

one-year monitoring study of 15 

additional airports with estimated lead 

emissions between 0.50 and 1.0 ton per 

year in an effort to better understand 

how these emissions affect 

concentrations of lead in the air at and 

near airports. Further, to help evaluate 

airport characteristics that could lead to 

ambient lead concentrations that 

approach or exceed the lead NAAQS, 

airports for this one-year monitoring 

study were selected based on factors 

such as the level of piston-engine 

aircraft activity and the predominant 

use of one runway due to wind patterns. 

As a result of these requirements, 

state and local air authorities collected 

and certified lead concentration data for 

at least one year at 17 airports with most 

monitors starting in 2012 and generally 

continuing through 2013. The data 


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114EPA (2015) Program Overview: Airport Lead 

Monitoring. EPA, Washington, DC, EPA–420–F–15– 

003, 2015. Available at: https://nepis.epa.gov/Exe/ 

ZyPDF.cgi/P100LJDW.PDF?Dockey=P100LJDW.PDF. 

115EPA (2022) Technical Support Document 

(TSD) for the EPA’s Proposed Finding that Lead 

Emissions from Aircraft Engines that Operate on 

Leaded Fuel Cause or Contribute to Air Pollution 

that May Reasonably Be Anticipated to Endanger 

Public Health and Welfare. EPA, Washington, DC, 

EPA–420–R–22–025, 2022. Available in the docket 

for this action. 

116A design value is a statistic that summarizes 

the air quality data for a given area in terms of the 

indicator, averaging time, and form of the standard. 

Design values can be compared to the level of the 

standard and are typically used to designate areas 

as meeting or not meeting the standard and assess 

progress towards meeting the NAAQS. 

117As noted earlier, when summarizing the 

available data regarding emissions of alkyl lead 

from piston-engine aircraft, the 2013 Lead ISA notes 

that an upper bound estimate of lead in the exhaust 

that might be in organic form may potentially be 20 

percent (2013 Lead ISA, p. 2–10). Organic lead in 

engine exhaust would be expected to influence 

receptors within short distances of the point of 

emission from piston-engine aircraft. Airports with 

large flight schools and/or facilities with substantial 

delays for aircraft queued for takeoff could 

experience higher concentrations of alkyl lead in 

the vicinity of the aircraft exhaust. 

118The data in Table 2 represent concentrations 

measured at one location at each airport and 

monitors were not consistently placed in close 

proximity to the run-up areas. As described in 

section II.A.3., monitored concentrations of lead in 

air near airports are highly influenced by proximity 

of the monitor to the run-up area. In addition to 

monitor placement, there are individual airport 

factors that can influence lead concentrations (e.g., 

the use of multiple run-up areas at an airport, fleet 

composition, and wind speed). The monitoring data 

reported in Table 2 reflect a range of lead 

concentrations indicative of the location at which 

measurements were made and the specific 

operations at an airport. 

119EPA (2020) Model-Extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

120EPA (2022) Technical Support Document 

(TSD) for the EPA’s Proposed Finding that Lead 

Emissions from Aircraft Engines that Operate on 

Leaded Fuel Cause or Contribute to Air Pollution 

that May Reasonably Be Anticipated to Endanger 

Public Health and Welfare. EPA, Washington, DC, 

EPA–420–R–22–025, 2022. Available in the docket 

for this action. 

121 In this study, the EPA defined the maximum 

impact site as 15 meters downwind of the tailpipe 

of an aircraft conducting run-up operations in the 

area designated for these operations at a runway 

end. The maximum impact area was defined as 

approximately 50 meters surrounding the maximum 

impact site. 

presented in Table 2 are based on the 

certified data for these sites and 

represent the maximum concentration 

monitored in a rolling three-month 

average for each location.114 115

TABLE 2—LEAD CONCENTRATIONS MONITORED AT 17 AIRPORTS IN THE U.S. 

Airport, State Lead design value,116

μg/m3

Auburn Municipal Airport, WA ............................................................................................................................................. 0.06 

Brookhaven Airport, NY ....................................................................................................................................................... 0.03 

Centennial Airport, CO ........................................................................................................................................................ 0.02 

Deer Valley Airport, AZ ........................................................................................................................................................ 0.04 

Gillespie Field, CA ............................................................................................................................................................... 0.07 

Harvey Field, WA ................................................................................................................................................................. 0.02 

McClellan-Palomar Airport, CA ............................................................................................................................................ 0.17 

Merrill Field, AK ................................................................................................................................................................... 0.07 

Nantucket Memorial Airport, MA ......................................................................................................................................... 0.01 

Oakland County International Airport, MI ............................................................................................................................ 0.02 

Palo Alto Airport, CA ........................................................................................................................................................... 0.12 

Pryor Field Regional Airport, AL .......................................................................................................................................... 0.01 

Reid-Hillview Airport, CA ..................................................................................................................................................... 0.10 

Republic Airport, NY ............................................................................................................................................................ 0.01 

San Carlos Airport, CA ........................................................................................................................................................ 0.33 

Stinson Municipal, TX .......................................................................................................................................................... 0.03 

Van Nuys Airport, CA .......................................................................................................................................................... 0.06 

Monitored lead concentrations 

violated the lead NAAQS at two airports 

in 2012: the McClellan-Palomar Airport 

and the San Carlos Airport. At both of 

these airports, monitors were located in 

close proximity to the area at the end of 

the runway most frequently used for 

pre-flight safety checks (i.e., run-up). 

Alkyl lead emitted by piston-engine 

aircraft would be expected to partition 

into the vapor phase and would not be 

collected by the monitoring conducted 

in this study, which is designed to 

quantitatively collect particulate forms 

of lead.117

Airport lead monitoring and modeling 

studies have identified the sharp 

decrease in lead concentrations with 

distance from the run-up area and 

therefore the importance of considering 

monitor placement relative to the runup area when evaluating the maximum 

impact location attributable to lead 

emissions from piston-engine aircraft. 

The monitoring data in Table 2 reflect 

differences in monitor placement 

relative to the run-up area as well as 

other factors; this study also provided 

evidence that air lead concentrations at 

and downwind from airports could be 

influenced by factors such as the use of 

more than one run-up area, wind speed, 

and the number of operations conducted 

by single- versus twin-engine aircraft.118

The EPA recognized that the airport 

lead monitoring study provided a small 

sample of the potential locations where 

emissions of lead from piston-engine 

aircraft could potentially cause 

concentrations of lead in ambient air to 

exceed the lead NAAQS. Because we 

considered that additional airports and 

conditions could lead to exceedances of 

the lead NAAQS at and near airports 

where piston-engine aircraft operate, 

and in order to understand the range of 

lead concentrations at airports 

nationwide, we developed an analysis 

of 13,000 airports in the peer-reviewed 

report titled, ‘‘Model-extrapolated 

Estimates of Airborne Lead 

Concentrations at U.S. Airports.’’ 119 120

This report provides estimated ranges of 

lead concentrations that may occur at 

and near airports where leaded avgas is 

used. The study extrapolated modeling 

results from one airport to estimate air 

lead concentrations at the maximum 

impact area near the run-up location for 

over 13,000 U.S. airports.121 The modelextrapolated lead estimates in this study 

indicate that some additional U.S. 

airports may have air lead 

concentrations above the NAAQS at this 

area of maximum impact. The report 

also indicates that, at the levels of 

activity analyzed at the 13,000 airports, 

estimated lead concentrations decrease 

to below the standard within 50 meters 


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72382 Federal Register / Vol. 88, No. 202 / Friday, October 20, 2023 / Rules and Regulations 

122Prior to this model extrapolation study, the 

EPA developed and evaluated an air quality 

modeling approach (this study is available here: 

https://nepis.epa.gov/Exe/ZyPDF.cgi/ 

P1007H4Q.PDF?Dockey=P1007H4Q.PDF), and 

subsequently applied the approach to a second 

airport and again performed an evaluation of the 

model output using air monitoring data (this second 

study is available here: https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf). 

123EPA (2022) Technical Support Document 

(TSD) for the EPA’s Proposed Finding that Lead 

Emissions from Aircraft Engines that Operate on 

Leaded Fuel Cause or Contribute to Air Pollution 

that May Reasonably Be Anticipated to Endanger 

Public Health and Welfare. EPA, Washington, DC, 

EPA–420–R–22–025, 2022. Available in the docket 

for this action. 

124EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

Table 6. p. 53. EPA, Washington, DC, EPA–420–R– 

20–003, 2020. 125See methods used in EPA (2020) Modelextrapolated Estimates of Airborne Lead 

Concentrations at U.S. Airports. Table 2. p.23. EPA, 

Washington, DC, EPA–420–R–20–003, 2020. 126EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports, 

Table 6. p.53. EPA, Washington, DC, EPA–420–R– 

20–003, 2020. 

127Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment 45: 5795–5804. 

128EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

Table 6. p.53. EPA, Washington, DC, EPA–420–R– 

20–003, 2020. 

129See EPA’s 2019 AirToxScreen. Available at 

https://www.epa.gov/AirToxScreen/2019- 

airtoxscreen. 

from the location of highest 

concentration. 

To estimate the potential ranges of 

lead concentrations at and downwind of 

the anticipated area of highest 

concentration at airports in the U.S., the 

relationship between piston-engine 

aircraft activity and lead concentration 

at and downwind of the maximum 

impact site at one airport was applied to 

piston-engine aircraft activity estimates 

for each U.S. airport.122 This approach 

for conducting a nationwide analysis of 

airports was selected due to the impact 

of piston-engine aircraft run-up 

operations on ground-level lead 

concentrations, which creates a 

maximum impact area that is expected 

to be generally consistent across 

airports. Specifically, these aircraft 

consistently take off into the wind and 

typically conduct run-up operations 

immediately adjacent to the take-off 

runway end, and thus, modeling lead 

concentrations from this source is 

constrained by variation in a few key 

parameters. These parameters include 

(1) total amount of piston-engine aircraft 

activity, (2) the proportion of activity 

conducted at one runway end, (3) the 

proportion of activity conducted by 

multi-piston-engine aircraft, (4) the 

duration of run-up operations, (5) the 

concentration of lead in avgas, (6) wind 

speed at the model airport relative to the 

extrapolated airport, and (7) additional 

meteorological, dispersion model, or 

operational parameters. These 

parameters were evaluated through 

sensitivity analyses as well as 

quantitative or qualitative uncertainty 

analyses. To generate robust 

concentration estimates, the EPA 

evaluated these parameters, conducted 

wind-speed correction of extrapolated 

estimates, and used airport-specific 

information regarding airport layout and 

prevailing wind directions for the 

13,000 airports.123

Results of this national analysis show 

that model-extrapolated three-month 

average lead concentrations in the 

maximum impact area may potentially 

exceed the lead NAAQS at some 

airports with activity ranging from 

3,616–26,816 Landing and Take-Off 

events (LTOs) in a three-month 

period.124 The lead concentration 

estimates from this model-extrapolation 

approach account for lead engine 

emissions from aircraft only, and do not 

include other sources of air-related lead. 

The broad range in LTOs that may lead 

to concentrations of lead exceeding the 

lead NAAQS is due to the piston-engine 

aircraft fleet mix at individual airports 

such that airports where the fleet is 

dominated by twin-engine aircraft 

would potentially reach concentrations 

of lead exceeding the lead NAAQS with 

fewer LTOs compared with airports 

where single-engine aircraft dominate 

the piston-engine fleet.125 Modelextrapolated three-month average lead 

concentrations from aircraft engine 

emissions were estimated to be above 

background for a distance of at least 500 

meters from the maximum impact area 

at airports with activity ranging from 

1,275–4,302 LTOs in that three-month 

period.126 In a separate modeling 

analysis at an airport at which hundreds 

of take-off and landing events by pistonengine aircraft occur per day, the EPA 

found that modeled 24-hour 

concentrations of lead from aircraft 

engine emissions were estimated to be 

above background for almost 1,000 

meters downwind from the runway.127

Model-extrapolated estimates of lead 

concentrations in the EPA report 

‘‘Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. 

Airports’’ were compared with 

monitored values reported in Table 2 

and show general agreement, suggesting 

that the extrapolation method presented 

in this report provides reasonable 

estimates of the range in concentrations 

of lead in air attributable to three-month 

activity periods of piston-engine aircraft 

at airports. The assessment included 

detailed evaluation of the potential 

impact of run-up duration, the 

concentration of lead in avgas, and the 

impact of meteorological parameters on 

model-extrapolated estimates of lead 

concentrations attributable to engine 

emissions of lead from piston-powered 

aircraft. Additionally, this study 

included a range of sensitivity analyses 

as well as quantitative and qualitative 

uncertainty analyses. 

The EPA’s model-extrapolation 

analysis of lead concentrations from 

engine emissions resulting from covered 

aircraft found that annual airport 

emissions of lead estimated to result in 

air lead concentrations potentially 

exceeding the NAAQS ranged from 0.1 

to 0.6 tons per year. There are key 

pieces of airport-specific data that are 

needed to fully evaluate the potential 

for piston-engine aircraft operating at an 

airport to cause concentrations of lead 

in the air to exceed the lead NAAQS, 

and the EPA’s report ‘‘Modelextrapolated Estimates of Airborne Lead 

Concentrations at U.S. Airports’’ 

provides quantitative and qualitative 

analyses of these factors.128 The EPA’s 

estimate for airports that have annual 

lead inventories of 0.1 ton or more are 

illustrative of and provide one approach 

for an initial screening evaluation of 

locations where engine emissions of 

lead from aircraft may increase localized 

lead concentrations in air. Airportspecific assessments would be needed 

to determine the magnitude of the 

potential range in lead concentrations at 

and downwind of each facility. 

As described in Section II.A.1 of this 

document, the FAA forecasts 0.9 

percent decreases in piston-engine 

aircraft activity out to 2041; however, 

these decreases are not projected to 

occur uniformly across airports. Among 

the more than 3,300 airports in the FAA 

TAF, the FAA forecasts both decreases 

and increases in general aviation, which 

is largely comprised of piston-engine 

aircraft. If the current conditions on 

which the forecast is based persist, then 

lead concentrations in the air may 

increase at the airports where general 

aviation activity is forecast to increase. 

In addition to airport-specific 

modeled estimates of lead 

concentrations, the EPA also provides 

annual estimates of lead concentrations 

for each census tract in the U.S. as part 

of the Air Toxics Screening Assessment 

(AirToxScreen).129 The census tract 

concentrations are averages of the areaweighted census block concentrations 

within the tract. Lead concentrations 

reported in the AirToxScreen are based 

on emissions estimates from 


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130These concentration estimates are not used for 

comparison to the level of the Lead NAAQS due to 

different temporal averaging times and underlying 

assumptions in modeling. The AirToxScreen 

estimates are provided to help state, local and 

Tribal air agencies and the public identify which 

pollutants, emission sources and places they may 

wish to study further to better understand potential 

risks to public health from air toxics. There are 

uncertainties inherent in these estimates described 

by the EPA, some of which are relevant to these 

estimates of lead concentrations; however, these 

estimates provide perspective on the potential 

influence of piston-engine emissions of lead on air 

quality. See https://www.epa.gov/AirToxScreen/ 

airtoxscreen-limitations. 

131As airports are generally in larger census 

blocks within a census tract, concentrations for 

airport blocks dominate the area-weighted average 

in cases where an airport is the predominant lead 

emissions source in a census tract. 

132Swiss FOCA (2007) Aircraft Piston Engine 

Emissions Summary Report. 33–05–003 Piston 

Engine Emissions_Swiss FOCA_Summary. Report_

070612_rit. Available at https://

www.bazl.admin.ch/bazl/en/home/specialists/ 

regulations-and-guidelines/environment/pollutantemissions/aircraft-engine-emissions/reportappendices--database--and-data-sheets.html. 

Retrieved on June 15, 2022. 

133 Griffith 2020. Electron microscopic 

characterization of exhaust particles containing lead 

dibromide beads expelled from aircraft burning 

leaded gasoline. Atmospheric Pollution Research 

11:1481–1486. 

134EPA (2013) ISA for Lead. Section 1.3. 

‘‘Exposure to Ambient Pb.’’ p. 1–11. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

135The EPA received comments on the 

information provided in this section to which we 

respond in the Response to Comments document 

for this action. 

136EPA (1977) Air Quality Criteria for Lead. 

Section 6.2.2.1. EPA, Washington, DC, EPA–600/8– 

77–017, 1977. 

137EPA (2006) Air Quality Criteria for Lead. 

Section E.6. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

138EPA (2006) Air Quality Criteria for Lead. 

Section E.6. p. 2–5. EPA, Washington, DC, EPA/ 

600/R–5/144aF, 2006. 

139EPA (2006) Air Quality Criteria for Lead. 

Section 2. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

140EPA (2013) ISA for Lead. Section 1.2.1. 

‘‘Sources, Fate and Transport of Ambient Pb;’’ p. 1– 

6; and Section 2.3. ‘‘Fate and Transport of Pb.’’ p. 

2–24 through 2–25. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

141Memorandum to Docket EPA–HQ–OAR– 

2022–0389. Deposition of Lead Emitted by Pistonengine Aircraft. June 15, 2022. Docket ID EPA–HQ– 

2022–0389. 

142EPA (2013) ISA for Lead. Section 2.6.1. 

‘‘Soils.’’ p. 2–118. EPA, Washington, DC, EPA/600/ 

R–10/075F, 2013. 

143EPA (2013) ISA for Lead. Chapter 6. 

‘‘Ecological Effects of Pb.’’ p. 6–57. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

144Murphy et al., 2008. Weekly patterns of 

aerosol in the United States. Atmospheric 

Chemistry and Physics. 8:2729–2739. 

145Lead concentrations collected as part of the 

Interagency Monitoring of Protected Visual 

Environments (IMPROVE) network and the 

National Oceanic and Atmospheric Administration 

(NOAA) monitoring sites. 

anthropogenic and natural sources of 

lead, including aircraft engine 

emissions.130 The 2019 AirToxScreen 

provides lead concentration estimates in 

air for 73,449 census tracts in the 

U.S.131 Lead concentrations associated 

with emissions from piston-engine 

aircraft comprised more than 50 percent 

of these census block area-weighted lead 

concentration estimates in over half of 

the census tracts, which included tracts 

in all 50 states, as well as Puerto Rico 

and the Virgin Islands. 

4. Fate and Transport of Emissions of 

Lead From Piston-Engine Aircraft 

This section summarizes the chemical 

transformation that piston-engine 

aircraft lead emissions are anticipated to 

undergo in the atmosphere and 

describes what is known about the 

deposition of piston-engine aircraft lead 

and its potential impacts on soil, food, 

and aquatic environments. 

a. Atmospheric Chemistry and 

Transport of Emissions of Lead From 

Piston-Engine Aircraft 

Lead emitted by piston-engine aircraft 

can have impacts in the local 

environment, and, due to their small 

size (i.e., typically less than one micron 

in diameter),132 133 lead-bearing particles 

emitted by piston engines may disperse 

widely in the environment. However, 

lead emitted during the landing and 

takeoff cycle, particularly during 

ground-based operations such as startup, idle, preflight run-up checks, taxi 

and the take-off roll on the runway, may 

deposit to the local environment and/or 

infiltrate into buildings.134 135

The Lead AQCDs summarize the 

literature reporting on the atmospheric 

chemical transformation of lead 

compounds emitted by engines 

operating on leaded fuel. Briefly, lead 

halides emitted by motor vehicles 

operating on leaded fuel were reported 

to undergo compositional changes upon 

cooling and mixing with the ambient air 

as well as during transport, and we 

would anticipate lead bromides emitted 

by piston-engine aircraft to behave 

similarly in the atmosphere. The water 

solubility of these lead-bearing particles 

was reported to be higher for the smaller 

lead-bearing particles.136 Lead halides 

emitted in motor vehicle exhaust were 

reported to break down rapidly in the 

atmosphere via redox reactions in the 

presence of atmospheric acids.137

Depending on ambient conditions (e.g., 

ozone and hydroxyl concentrations in 

the atmosphere), alkyl lead may exist in 

the atmosphere for hours to days 138 and 

may therefore be transported off airport 

property into nearby communities. 

Tetraethyl lead reacts with the hydroxyl 

radical in the gas phase to form a variety 

of products that include ionic trialkyl 

lead, dialkyl lead and metallic lead. 

Trialkyl lead is slow to react with the 

hydroxyl radical and is quite persistent 

in the atmosphere.139

b. Deposition of Lead Emissions From 

Piston-Engine Aircraft and Soil Lead 

Concentrations to Which Piston-Engine 

Aircraft May Contribute 

Lead is removed from the atmosphere 

and deposited on soil, into aquatic 

systems and on other surfaces via wet or 

dry deposition.140 Meteorological 

factors (e.g., wind speed, convection, 

rain, humidity) influence local 

deposition rates. With regard to 

deposition of lead from aircraft engine 

emissions, the EPA modeled the 

deposition rate for aircraft lead 

emissions at one airport in a temperate 

climate in California with dry summer 

months. In this location, the average 

lead deposition rate from aircraft 

emissions of lead was 0.057 milligrams 

per square meter per year.141

Studies summarized in the 2013 Lead 

ISA suggest that soil is a reservoir for 

contemporary and historical emissions 

of lead to air.142 Once deposited to soil, 

lead can be absorbed onto organic 

material, can undergo chemical and 

physical transformation depending on a 

number of factors (e.g., pH of the soil 

and the soil organic content), and can 

participate in further cycling through air 

or other media.143 The extent of 

atmospheric deposition of lead from 

aircraft engine emissions would be 

expected to depend on a number of 

factors including the size of the particles 

emitted (smaller particles, such as those 

in aircraft emissions, have lower settling 

velocity and may travel farther distances 

before being deposited compared with 

larger particles), the temperature of the 

exhaust (the high temperature of the 

exhaust creates plume buoyancy), as 

well as meteorological factors (e.g., 

wind speed, precipitation rates). As a 

result of the size of the lead particulate 

matter emitted from piston-engine 

aircraft and as a result of these 

emissions occurring at various altitudes, 

lead emitted from these aircraft may 

distribute widely through the 

environment.144 Murphy et al. (2008) 

reported weekend increases in ambient 

air lead concentrations monitored at 

remote locations in the U.S. that the 

authors hypothesized were related to 

weekend increases in piston-engine 

powered general aviation activity.145

Heiken et al. (2014) assessed air lead 

concentrations potentially attributable 

to resuspended lead that previously 

deposited onto soil relative to air lead 

concentrations resulting directly from 


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146Heiken et al., 2014. ACRP Web-Only 

Document 21: Quantifying Aircraft Lead Emissions 

at Airports. Contractor’s Final Report for ACRP 02– 

34. Available at https://www.trb.org/Publications/ 

Blurbs/172599.aspx. 

147McCumber and Strevett 2017. A Geospatial 

Analysis of Soil Lead Concentrations Around 

Regional Oklahoma Airports. Chemosphere 167:62– 

70. 

148 Kavouras et al., 2013. Bioavailable Lead in 

Topsoil Collected from General Aviation Airports. 

The Collegiate Aviation Review International 

31(1):57–68. Available at https://doi.org/10.22488/ 

okstate.18.100438. 

149Heiken et al., 2014. ACRP Web-Only 

Document 21: Quantifying Aircraft Lead Emissions 

at Airports. Contractor’s Final Report for ACRP 02– 

34. Available at https://www.trb.org/Publications/ 

Blurbs/172599.aspx. 

150EPA (2010) Development and Evaluation of an 

Air Quality Modeling Approach for Lead Emissions 

from Piston-Engine Aircraft Operating on Leaded 

Aviation Gasoline. EPA, Washington, DC, EPA– 

420–R–10–007, 2010. https://nepis.epa.gov/Exe/ 

ZyPDF.cgi/ 

P1007H4Q.PDF?Dockey=P1007H4Q.PDF. 

151Environment Canada (2000) Airborne 

Particulate Matter, Lead and Manganese at 

Buttonville Airport. Toronto, Ontario, Canada: 

Conor Pacific Environmental Technologies for 

Environmental Protection Service, Ontario Region. 

152Lejano and Ericson 2005. Tragedy of the 

Temporal Commons: Soil-Bound Lead and the 

Anachronicity of Risk. Journal of Environmental 

Planning and Management. 48(2):301–320. 

153EPA (2013) ISA for Lead. Section 3.1.3.3. 

‘‘Dietary Pb Exposure.’’ p. 3–20 through 3–24. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

154EPA (2006) Air Quality Criteria for Lead. 

Section 8.2.2. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

155EPA (2006) Air Quality Criteria for Lead. 

Section 8.2.2. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

156O’Connor-Marer. Aerial Applicator’s Manual: 

A National Pesticide Applicator Certification Study 

Guide. p. 40. National Association of State 

Departments of Agriculture Research Foundation. 

Available at https://www.epa.gov/system/files/ 

documents/2022-09/national-pesticide-applicatorcert-core-manual-2014.pdf. 

157The additive used in the fuel to scavenge lead 

determines the chemical form of the lead halide 

emitted; because ethylene dibromide is added to 

leaded aviation gasoline used in piston-engine 

aircraft, the lead halide emitted is in the form of 

lead dibromide. 

158EPA (2006) Air Quality Criteria for Lead. pp. 

7–9 and AXZ7–39 (citing U.S. studies of the 1990s). 

EPA, Washington, DC, EPA/600/R–5/144aF, 2006. 

159EPA (2006) Air Quality Criteria for Lead. p. 

AXZ7–39. EPA, Washington, DC, EPA/600/R–5/ 

144aF, 2006. 

160EPA (1986) Air Quality Criteria for Lead. 

Sections 6.5.3. EPA, Washington, DC, EPA–600/8– 

83/028aF–dF (NTIS PB87142386), 1986. 

161EPA (1986) Air Quality Criteria for Lead. 

Section 7.2.2.2.1.EPA, Washington, DC, EPA–600/ 

8–83/028aF–dF (NTIS PB87142386), 1986. 

162EPA (1986) Air Quality Criteria for Lead. 

Section 7.2.2.2.2. EPA, Washington, DC, EPA–600/ 

8–83/028aF–dF (NTIS PB87142386), 1986. 

163EPA (2013) ISA for Lead. Section 6.4.2. 

‘‘Biogeochemistry and Chemical Effects of Pb in 

Freshwater and Saltwater Systems.’’ p. 6–147. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

164EPA (2002) Persistent, Bioaccumulative, and 

Toxic Pollutants (PBT) Program. PBT National 

Action Plan for Alkyl-Pb. Washington, DC. June. 

2002. 

165See FAA’s NASR. Available at https://

www.faa.gov/air_traffic/flight_info/aeronav/aero_

data/eNASR_Browser/. 

aircraft engine emissions.146 Based on 

comparisons of lead concentrations in 

total suspended particulate (TSP) and 

fine particulate matter (PM2.5) measured 

at the three airports, coarse particle lead 

was observed to account for about 20– 

30 percent of the lead found in TSP. The 

authors noted that based on analysis of 

lead isotopes present in the air samples 

collected at these airports, the original 

source of the lead found in the coarse 

particle range appeared to be from 

aircraft exhaust emissions of lead that 

previously deposited to soil and were 

resuspended by wind or aircraftinduced turbulence. Results from lead 

isotope analysis in soil samples 

collected at the same three airports led 

the authors to conclude that lead 

emitted from piston-engine aircraft was 

not the dominant source of lead in soil 

in the samples measured at the airports 

they studied. The authors note the 

complex history of topsoil can create 

challenges in understanding the extent 

to which aircraft lead emissions impact 

soil lead concentrations at and near 

airports (e.g., the source of topsoil can 

change as a result of site renovation, 

construction, landscaping, natural 

events such as wildfire and hurricanes, 

and other activities). Concentrations of 

lead in soil at and near airports 

servicing piston-engine aircraft have 

been measured using a range of 

approaches.147 148 149 150 151 152 Kavouras 

et al. (2013) collected soil samples at 

three airports and reported that 

construction at an airport involving 

removal and replacement of topsoil 

complicated interpretation of the 

findings at that airport and that the 

number of runways at an airport may 

influence resulting lead concentrations 

in soil (i.e., multiple runways may 

provide for more wide-spread dispersal 

of the lead over a larger area than that 

potentially affected at a single-runway 

airport). 

c. Potential for Lead Emissions From 

Piston-Engine Aircraft To Impact 

Agricultural Products 

Studies conducted near stationary 

sources of lead emissions (e.g., smelters) 

have shown that atmospheric lead 

sources can lead to contamination of 

agricultural products, such as 

vegetables.153 154 In this way, air lead 

sources may contribute to dietary 

exposure pathways.155 As described in 

section II.A.1. of this document, pistonengine aircraft are used in the 

application of pesticides, fertilizers and 

seeding crops for human and animal 

consumption and, as such, provide a 

potential route of exposure for lead in 

food. To minimize drift of pesticides 

and other applications from the 

intended target, pilots are advised to 

maintain a height between eight and 12 

feet above the target crop during 

application.156 An unintended 

consequence of this practice is that 

exhaust emissions of lead have a 

substantially increased potential for 

directly depositing on vegetation and 

surrounding soil. Lead halides, the 

primary form of lead emitted by engines 

operating on leaded fuel,157 are slightly 

water soluble and, therefore, may be 

more readily absorbed by plants than 

other forms of inorganic lead. 

The 2006 AQCD indicated that 

surface deposition of lead onto plants 

may be significant.158 Atmospheric 

deposition of lead provides a pathway 

for lead in vegetation as a result of 

contact with above-ground portions of 

the plant.159 160 161 Livestock may 

subsequently be exposed to lead in 

vegetation (e.g., grasses and silage) and 

in surface soils via incidental ingestion 

of soil while grazing.162

d. Potential for Lead Emissions From 

Piston-Engine Aircraft To Impact 

Aquatic Ecosystems 

As discussed in section 6.4 of the 

2013 Lead ISA, lead bioaccumulates in 

the tissues of aquatic organisms through 

ingestion of food and water or direct 

uptake from the environment (e.g., 

across membranes such as gills or 

skin).163 Alkyl lead, in particular, has 

been identified by the EPA as a 

Persistent, Bioaccumulative, and Toxic 

(PBT) pollutant.164 There are 527 

seaport facilities in the U.S., and 

landing and take-off activity by 

seaplanes at these facilities provides a 

direct pathway for emission of organic 

and inorganic lead to the air near/above 

inland waters and ocean seaports where 

these aircraft operate.165 Inland airports 

may also provide a direct pathway for 

emission of organic and inorganic lead 

to the air near/above inland waters. 

Lead emissions from piston-engine 

aircraft operating at seaplane facilities 

as well as airports and heliports near 

water bodies can enter the aquatic 

ecosystem by either deposition from 

ambient air or runoff of lead deposited 

to surface soils. 

In addition to deposition of lead from 

engine emissions by piston-powered 

aircraft, lead may enter aquatic systems 

from the pre-flight inspection of the fuel 

for contaminants that pilots conduct. 

While some pilots return the checked 

fuel to their fuel tank or dispose of it in 

a receptacle provided on the airfield, 

some pilots discard the fuel onto the 

tarmac, ground, or water, in the case of 


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166National Academies of Sciences, Engineering, 

and Medicine 2014. Best Practices for General 

Aviation Aircraft Fuel-Tank Sampling. Washington, 

DC: The National Academies Press. https://doi.org/ 

10.17226/22343. 

167Memorandum to Docket EPA–HQ–OAR– 

2022–0389. Potential Exposure to Non-exhaust Lead 

and Ethylene Dibromide. June 15, 2022. Docket ID 

EPA–HQ–2022–0389. 

168As described in this section, the EPA 

evaluated environmental justice consistent with the 

EPA 2016 Technical Guidance. However, the final 

decisions in this action are based on EPA’s 

consideration under CAA section 231(a)(2)(A) of 

potential risks to public health and welfare from the 

lead air pollution, as well as its evaluation of 

whether emissions of lead from engines in covered 

aircraft contribute to that air pollution. See section 

III. for further discussion of the statutory authority 

for this action and sections IV. and V. for further 

discussion of the basis for these findings. 

169See, https://www.federalregister.gov/ 

documents/2023/04/26/2023-08955/revitalizingour-nations-commitment-to-environmental-justicefor-all. When the analysis discussed in this section 

was performed, EPA defined 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. 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 regulatory Agency’s 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.’’ See, EPA’s Guidance on 

Considering Environmental Justice During the 

Development of Regulatory Actions. Available at 

https://www.epa.gov/sites/default/files/2015-06/ 

documents/considering-ej-in-rulemaking-guidefinal.pdf. See also https://www.epa.gov/ 

environmentaljustice. 170EPA (2013) ISA for Lead. Section 5.4. 

‘‘Summary.’’ p. 5–40. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

171EPA. America’s Children and the 

Environment. Summary of blood lead levels in 

children updated in 2022, available at https://

www.epa.gov/americaschildrenenvironment/ 

biomonitoring-lead. Data source: Centers for Disease 

Control and Prevention, National Report on Human 

Exposure to Environmental Chemicals. Blood Lead 

(2011–2018). Updated March 2022. Available at 

https://www.cdc.gov/exposurereport/report/pdf/ 

cgroup2_LBXBPB_2011-p.pdf. 

172The relative contribution of lead emissions 

from covered aircraft engines to these disparities 

has not been determined and is not a goal of the 

evaluation described here. 

173This analysis used the U.S. Census and 

demographic data from 2010 which was the most 

recent data available at the time of this assessment. 

174Residential proximity to a source of a specific 

air pollutant(s) is a widely used surrogate measure 

to evaluate the potential for higher exposures to that 

pollutant (EPA 2016 Technical Guidance for 

Assessing Environmental Justice in Regulatory 

Analysis. Section 4.2.1). Data presented in section 

II.A.3. demonstrate that lead concentrations in air 

near the runup area can exceed the lead NAAQS 

and concentrations decrease sharply with distance 

from the ground-based aircraft exhaust and vary 

with the amount of aircraft activity at an airport. 

Not all people living within 500 meters of a runway 

are expected to be equally exposed to lead. 

175Miranda et al., 2011. A Geospatial Analysis of 

the Effects of Aviation Gasoline on Childhood 

Blood Lead Levels. Environmental Health 

Perspectives. 119:1513–1516. 

176Zahran et al., 2017. The Effect of Leaded 

Aviation Gasoline on Blood Lead in Children. 

Journal of the Association of Environmental and 

Resource Economists. 4(2):575–610. 

177Zahran et al., 2022. Leaded Aviation Gasoline 

Exposure Risk and Child Blood Lead Levels. 

Proceedings of the National Academy of Sciences 

Nexus. 2:1–11. 

a fuel check being conducted on a 

seaplane. Lead in the fuel discarded to 

the environment may evaporate to the 

air and may be taken up by the surface 

on which it is discarded. Lead on 

tarmac or soil surfaces is available for 

runoff to surface water. Tetraethyl lead 

in the avgas directly discarded to water 

will be available for uptake and 

bioaccumulation in aquatic life. The 

National Academy of Sciences Airport 

Cooperative Research Program (ACRP) 

conducted a survey study of pilots’ fuel 

sampling and disposal practices. Among 

the 146 pilots responding to the survey, 

36 percent indicated they discarded all 

fuel check samples to the ground 

regardless of contamination status, and 

19 percent of the pilots indicated they 

discarded only contaminated fuel to the 

ground.166 Leaded avgas discharged to 

the ground and water includes other 

hazardous fuel components such as 

ethylene dibromide.167

5. Consideration of Environmental 

Justice and Children in Populations 

Residing Near Airports 

This section provides a description of 

how many people live in close 

proximity to airports where they may be 

exposed to airborne lead from aircraft 

engine emissions of lead (referred to 

here as the ‘‘near-airport’’ population). 

This section also provides the 

demographic composition of the nearairport population, with attention to 

implications related to environmental 

justice (EJ) and the population of 

children in this near-source 

environment.168

Executive Order 14096, ‘‘Revitalizing 

Our Nation’s Commitment to 

Environmental Justice for All,’’ defines 

environmental justice as ‘‘the just 

treatment and meaningful involvement 

of all people, regardless of income, race, 

color, national origin, Tribal affiliation, 

or disability, in agency decision-making 

and other Federal activities that affect 

human health and the environment so 

that people: (i) are fully protected from 

disproportionate and adverse human 

health and environmental effects 

(including risks) and hazards, including 

those related to climate change, the 

cumulative impacts of environmental 

and other burdens, and the legacy of 

racism or other structural or systemic 

barriers; and (ii) have equitable access to 

a healthy, sustainable, and resilient 

environment in which to live, play, 

work, learn, grow, worship, and engage 

in cultural and subsistence 

practices.’’ 169 Providing this 

information regarding potential EJ 

implications in the population living 

near airports is important for purposes 

of public information and awareness. 

Here, EPA finds that blood lead levels 

in children from low-income 

households remain higher than those in 

children from higher income 

households, and blood lead levels in 

Black children are higher than those in 

non-Hispanic White children.170 171 172

The analysis described here provides 

information regarding whether some 

demographic groups are more highly 

represented in the near-airport 

environment compared with people 

who live farther from airports.173

Residential proximity to airports 

implies that there is an increased 

potential for exposure to lead from 

covered aircraft engine emissions.174 As 

described in section II.A.3. of this 

document, several studies have 

measured higher concentrations of lead 

in air near airports with piston-engine 

aircraft activity. Additionally, as noted 

in section II.A. of this document, three 

studies have reported increased blood 

lead levels in children with increasing 

proximity to airports.175 176 177

We first summarize here the literature 

on disparity among near-airport 

populations. Then we describe the 

analyses the EPA conducted to evaluate 

potential disparity in the population 

groups living near runways where 

piston-engine aircraft operate compared 

to those living elsewhere. 

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 


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178Rowangould 2013. A census of the nearroadway population: public health and 

environmental justice considerations. 

Transportation Research Part D 25:59–67. https:// 

dx.doi.org/10.1016/j.trd.2013.08.003. 

179Marshall et al., 2014. Prioritizing 

environmental justice and equality: diesel 

emissions in Southern California. Environmental 

Science & Technology 48: 4063–4068. https://

doi.org/10.1021/es405167f. 

180Marshall 2008. Environmental inequality: air 

pollution exposures in California’s South Coast Air 

Basin. Atmospheric Environment 21:5499–5503. 

https://doi.org/10.1016/j.atmosenv.2008.02.005. 

181Tessum et al., 2021. PM2.5 polluters 

disproportionately and systemically affect people of 

color in the United States. Science Advances 

7:eabf4491. 

182Mohai et al., 2009. Environmental justice. 

Annual Reviews 34:405–430. Available at https://

doi.org/10.1146/annurev-environ-082508-094348. 

183McNair 2020. Investigation of environmental 

justice analysis in airport planning practice from 

2000 to 2010. Transportation Research Part D 

81:102286. 

184Woodburn 2017. Investigating neighborhood 

change in airport-adjacent communities in 

multiairport regions from 1970 to 2010. Journal of 

the Transportation Research Board, 2626, 1–8. 

185Rissman et al., 2013. Equity and health 

impacts of aircraft emissions at the HartfieldJackson Atlanta International Airport. Landscape 

and Urban Planning, 120: 234–247. 

186EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

187EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

EPA, Washington, DC, EPA–420–R–20–003, 2020. 

188Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment, 45 (32), 5795–5804. 

DOI: https://dx.doi.org/10.1016/j.atmosenv.

2011.07.017. 

189We do not assume or expect that all people 

living within 500m or 1,000m of a runway are 

exposed to lead from piston-engine aircraft 

emissions, and the wide range of activity of pistonengine aircraft at airports nationwide suggests that 

exposure to lead from aircraft emissions is likely to 

vary widely. 

190 In this analysis, we included populations 

living in census blocks that intersected the 500- 

meter buffer around each runway in the U.S. 

Potential uncertainties in this approach are 

described in our report National Analysis of the 

Populations Residing Near or Attending School 

Near U.S. Airports. EPA–420–R–20–001, available 

at https://nepis.epa.gov/Exe/ZyPDF.cgi?

Dockey=P100YG4A.pdf, and in the EPA responses 

to peer review comments on the report, available 

here: https://nepis.epa.gov/Exe/ZyPDF.cgi?

Dockey=P100YISM.pdf. 

191EPA (2020) National Analysis of the 

Populations Residing Near or Attending School 

Near U.S. Airports. EPA–420–R–20–001. Available 

at https://nepis.epa.gov/Exe/ZyPDF.cgi?

Dockey=P100YG4A.pdf. 

192Clarke. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Estimation of Population Size and 

Demographic Characteristics among People Living 

Near Airports by State in the United States. May 31, 

2022. Docket ID EPA–HQ–2022–0389. 

193Clarke. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Estimation of Population Size and 

Demographic Characteristics among People Living 

Near Airports by State in the United States. May 31, 

2022. Docket ID EPA–HQ–2022–0389. 

194These data are presented in tabular form for 

all states in this memorandum located in the 

docket: Clarke. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Estimation of Population Size and 

Demographic Characteristics among People Living 

Near Airports by State in the United States. May 31, 

2022. Docket ID EPA–HQ–2022–0389. 

of the population compared with the 

general population, including near 

transportation sources.178 179 180 181 182

The literature includes studies that have 

reported on communities in close 

proximity to airports that are 

disproportionately represented by 

people of color and low-income 

populations. McNair (2020) described 

nineteen major airports that underwent 

capacity expansion projects between 

2000 and 2010, thirteen of which had a 

large concentration or presence of 

persons of color, foreign-born persons or 

low-income populations nearby.183

Woodburn (2017) reported 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.184 Rissman et al. (2013) 

reported that with increasing proximity 

to the Hartsfield-Jackson Atlanta 

International Airport, exposures to 

particulate matter were higher, and 

there were lower home values, income, 

education, and percentage of white 

residents.185

The EPA used two approaches to 

understand whether some members of 

the population (e.g., children five and 

under, people of color, indigenous 

populations, low-income populations) 

represent a larger share of the people 

living in proximity to airports where 

piston-engine aircraft operate compared 

with people who live farther away from 

these airports. In the first approach, we 

evaluated people living within, and 

children attending school within, 500 

meters of all of the approximately 

20,000 airports in the U.S., using 

methods described in the EPA’s report 

titled ‘‘National Analysis of the 

Populations Residing Near or Attending 

School Near U.S. Airports.’’ 186 In the 

second approach, we evaluated people 

living near the NPIAS airports in the 

conterminous 48 states. As noted in 

section II.A.1. of this document, the 

NPIAS airports support the majority of 

piston-engine aircraft activity that 

occurs in the U.S. Among the NPIAS 

airports, we compared the demographic 

composition of people living within one 

kilometer of runways with the 

demographic composition of people 

living at a distance of one to five 

kilometers from the same airports. 

The distances analyzed for those 

people living closest to airports (i.e., 

distances of 500 meters and 1,000 

meters) were chosen for evaluation 

following from the air quality 

monitoring and modeling data 

presented in section II.A.3. of this 

document. Specifically, the EPA’s 

modeling and monitoring data indicate 

that concentrations of lead from pistonengine aircraft emissions can be 

elevated above background levels at 

distances of 500 meters over a rolling 

three-month period. On individual days, 

concentrations of lead from pistonengine aircraft emissions can be 

elevated above background levels at 

distances of 1,000 meters downwind of 

a runway, depending on aircraft activity 

and prevailing wind direction.187 188 189

Because the U.S. has a dense network 

of airports, many of which have 

neighboring communities, we quantified 

the number of people living and 

children attending school within 500 

meters of the approximately 20,000 

airports in the U.S.190 From this 

analysis, the EPA estimates that 

approximately 5.2 million people live 

within 500 meters of an airport runway, 

363,000 of whom are children aged five 

and under. The EPA also estimates that 

573 schools attended by 163,000 

children in kindergarten through twelfth 

grade are within 500 meters of an 

airport runway.191

In order to identify potential 

disparities in the near-airport 

population, we also evaluated 

populations at the state level. Using the 

U.S. Census population data for each 

state in the U.S., we compared the 

percent of people by age, race and 

indigenous peoples (i.e., children five 

and under, Black, Asian, and Native 

American or Alaska Native) living 

within 500 meters of an airport runway 

with the percent by age, race, and 

indigenous peoples comprising the state 

population.192 Using the methodology 

described in Clarke (2022), the EPA 

identified states in which children, 

Black, Asian, and Native American or 

Alaska Native populations represent a 

greater fraction of the population living 

within 500 meters of a runway 

compared with the percent of these 

groups in the state population.193

Results of this analysis are presented in 

the following tables.194 This state-level 

analysis presents summary information 

for a subset of potentially relevant 

demographic characteristics. We present 

data in this section regarding a wider 

array of demographic characteristics 

when evaluating populations living near 

NPIAS airports. 

Among children five and under, there 

were three states (Nevada, South 

Carolina, and South Dakota) in which 

the percent of children five and under 


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living within 500 meters of a runway 

represents a greater fraction of the 

population by a difference of one 

percent or greater compared with the 

percent of children five and under in 

the state population (Table 3). 

TABLE 3—THE POPULATION OF CHILDREN FIVE YEARS AND UNDER WITHIN 500 METERS OF AN AIRPORT RUNWAY

COMPARED TO THE STATE POPULATION OF CHILDREN FIVE YEARS AND UNDER

State 

Percent of 

children aged 

five years and 

under within 

500 meters 

Percent of 

children aged 

five years and 

under within 

the state 

Number of 

children aged 

five years and 

under within 

500 meters 

Number of 

children aged 

five years and 

under in 

the state 

Nevada ..................................................................................... 10 8 1000 224,200 

South Carolina ......................................................................... 9 8 400 361,400 

South Dakota ........................................................................... 11 9 3,000 71,300 

There were nine states in which the 

Black population represented a greater 

fraction of the population living in the 

near-airport environment by a difference 

of one percent or greater compared with 

the state as a whole. These states were 

California, Kansas, Kentucky, Louisiana, 

Mississippi, Nevada, South Carolina, 

West Virginia, and Wisconsin (Table 4). 

TABLE 4—THE BLACK POPULATION WITHIN 500 METERS OF AN AIRPORT RUNWAY AND THE BLACK POPULATION, BY

STATE

State Percent black 

within 500 meters 

Percent black 

within the state 

Black population 

within 500 meters 

Black population 

in the state 

California .................................................................................. 8 7 18,981 2,486,500 

Kansas ..................................................................................... 8 6 1,240 173,300 

Kentucky .................................................................................. 9 8 3,152 342,800 

Louisiana .................................................................................. 46 32 14,669 1,463,000 

Mississippi ................................................................................ 46 37 8,542 1,103,100 

Nevada ..................................................................................... 12 9 1,794 231,200 

South Carolina ......................................................................... 31 28 10,066 1,302,900 

West Virginia ............................................................................ 10 3 1,452 63,900 

Wisconsin ................................................................................. 9 6 4,869 367,000 

There were three states with a greater 

fraction of Asians in the near-airport 

environment compared with the state as 

a whole by a difference of one percent 

or greater: Indiana, Maine, and New 

Hampshire (Table 5). 

TABLE 5—THE ASIAN POPULATION WITHIN 500 METERS OF AN AIRPORT RUNWAY AND THE ASIAN POPULATION, BY STATE

State Percent asian 

within 500 meters 

Percent asian 

within the state 

Asian population 

within 500 meters 

Asian population 

in the state 

Indiana ..................................................................................... 4 2 1,681 105,500 

Maine ....................................................................................... 2 1 406 13,800 

New Hampshire ....................................................................... 4 2 339 29,000 

There were five states (Alaska, 

Arizona, Delaware, South Dakota, and 

New Mexico) where the near-airport 

population had greater representation 

by Native Americans and Alaska 

Natives compared with the portion of 

the population they comprise at the 

state level by a difference of one percent 

or greater. In Alaska, the disparity in 

residential proximity to a runway was 

the largest: 16,020 Alaska Natives were 

estimated to live within 500 meters of 

a runway, representing 48 percent of the 

population within 500 meters of an 

airport runway. In contrast, Alaska 

Natives comprise 15 percent of the 

Alaska state population (Table 6). 


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195For this analysis, we evaluated the 2,022 

airports with a population of greater than 100 

people inside the zero to one kilometer distance to 

avoid low population counts distorting the 

assessment of percent contributions of each group 

to the total population within the zero to one 

kilometer distance. 196 Kamal et al., Memorandum to Docket EPA– 

HQ–OAR–2022–0389. Analysis of Potential 

Disparity in Residential Proximity to Airports in the 

Conterminous United States. May 24, 2022. Docket 

ID EPA–HQ–2022–0389. Methods used are 

described in this memo and include the use of 

block group resolution data to evaluate the 

representation of different demographic groups 

near-airport and for those living one to five 

kilometers away. 

197This analysis of 2,022 NPIAS airports did not 

include airports in Alaska. 

198 Kamal et al., Memorandum to Docket EPA– 

HQ–OAR–2022–0389. Analysis of Potential 

Disparity in Residential Proximity to Airports in the 

Conterminous United States. May 24, 2022. Docket 

ID EPA–HQ–2022–0389. 

TABLE 6—THE NATIVE AMERICAN AND ALASKA NATIVE POPULATION WITHIN 500 METERS OF AN AIRPORT RUNWAY AND

THE NATIVE AMERICAN AND ALASKA NATIVE POPULATION, BY STATE

State 

Percent Native 

American and 

Alaska Native 

within 500 meters 

Percent Native 

American and 

Alaska Native 

within the state 

Native American 

and Alaska 

Native population 

within 500 meters 

Native American 

and Alaska 

Native population 

in the state 

Alaska ...................................................................................... 48 15 16,020 106,300 

Arizona ..................................................................................... 18 5 5,017 335,300 

Delaware .................................................................................. 2 1 112 5,900 

New Mexico ............................................................................. 21 10 2,265 208,900 

South Dakota ........................................................................... 22 9 1,606 72,800 

In a separate analysis, the EPA 

focused on evaluating the potential for 

disparities in populations residing near 

the NPIAS airports. The EPA compared 

the demographic composition of people 

living within one kilometer of runways 

at 2,022 of the approximately 3,300 

NPIAS airports with the demographic 

composition of people living at a 

distance of one to five kilometers from 

the same airports.195 196 In this analysis, 

over one-fourth of airports (i.e., 515) 

were identified at which children under 

five were more highly represented in the 

zero to one kilometer distance compared 

with the percent of children under five 

living one to five kilometers away 

(Table 7). There were 666 airports where 

people of color had a greater presence 

in the zero to one kilometer area closest 

to airport runways than in populations 

farther away. There were 761 airports 

where people living at less than twotimes the Federal Poverty Level 

represented a higher proportion of the 

overall population within one kilometer 

of airport runways compared with the 

proportion of people living at less than 

two times the Federal Poverty Level 

among people living one to five 

kilometers away. 

TABLE 7—NUMBER OF AIRPORTS (AMONG THE 2,022 AIRPORTS EVALUATED) WITH DISPARITY FOR CERTAIN DEMOGRAPHIC POPULATIONS WITHIN ONE KILOMETER OF AN AIRPORT RUNWAY IN RELATION TO THE COMPARISON POPULATION BETWEEN ONE AND FIVE KILOMETERS FROM AN AIRPORT RUNWAY

Demographic group 

Number of airports with disparity 

Total airports 

with disparity 

Disparity 

1–5% 

Disparity 

5–10% 

Disparity 

10–20% 

Disparity 

20%+ 

Children under five years of age ....................................... 515 507 7 1 0 

People with income less than twice the Federal Poverty 

Level ............................................................................... 761 307 223 180 51 

People of Color (all non-White races, ethnicities and indigenous peoples) .......................................................... 666 377 126 123 40 

Non-Hispanic Black ............................................................ 405 240 77 67 21 

Hispanic ............................................................................. 551 402 85 47 17 

Non-Hispanic Asian ........................................................... 268 243 18 4 3 

Non-Hispanic Native American or Alaska Native 197 ......... 144 130 6 7 1 

Non-Hispanic Hawaiian or Pacific Islander ....................... 18 17 1 0 0 

Non-Hispanic Other Race .................................................. 11 11 0 0 0 

Non-Hispanic Two or More Races .................................... 226 226 0 0 0 

To understand the extent of the 

potential disparity among the 2,022 

NPIAS airports, Table 7 provides 

information about the distribution in the 

percent differences in the proportion of 

children, individuals with incomes 

below two times the Federal Poverty 

Level, and people of color living within 

one kilometer of a runway compared 

with those living one to five kilometers 

away. For children, Table 7 indicates 

that for the vast majority of these 

airports where there is a higher 

percentage of children represented in 

the near-airport population, differences 

are relatively small (e.g., less than five 

percent). For the airports where 

disparity is evident on the basis of 

poverty, race and ethnicity, the 

disparities are potentially large, ranging 

up to 42 percent for those with incomes 

below two times the Federal Poverty 

Level, and up to 45 percent for people 

of color.198

There are uncertainties in the results 

provided here inherent to the proximitybased approach used. These 

uncertainties include the use of block 

group data to provide population 

numbers for each demographic group 

analyzed, and uncertainties in the 

Census data, including from the use of 

data from different analysis years (e.g., 

2010 Census Data and 2018 income 

data). These uncertainties are described 


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199 Kamal et al., Memorandum to Docket EPA– 

HQ–OAR–2022–0389. Analysis of Potential 

Disparity in Residential Proximity to Airports in the 

Conterminous United States. May 24, 2022. Docket 

ID EPA–HQ–2022–0389. 

200 During the public comment period on the 

proposed findings for this action, commenters 

provided an additional evaluation of populations 

living near airports that they conclude to indicate 

that disparity by race and income is larger and 

occurs more frequently at airports that have the 

highest lead emissions and the highest residential 

population density compared with airports where 

less lead is emitted and population density is lower. 

This comment is available in the docket at 

regulations.gov: EPA–HQ–OAR–2022–0389–0238. 

201Zahran et al., 2022. Leaded Aviation Gasoline 

Exposure Risk and Child Blood Lead Levels. 

Proceedings of the National Academy of Sciences 

Nexus. 2:1–11. 

202Federal Lead Action Plan to Reduce 

Childhood Lead Exposures and Associated Health 

Impacts. (2018) President’s Task Force on 

Environmental Health Risks and Safety Risks to 

Children. Available at https://www.epa.gov/sites/ 

default/files/2018-12/documents/fedactionplan_

lead_final.pdf. 

203EPA (2022) EPA Strategy to Reduce Lead 

Exposures and Disparities in U.S. Communities. 

EPA 540R22006. Available at https://www.epa.gov/ 

system/files/documents/2022-11/Lead%20Strategy_

1.pdf. 

204 41 FR 14921 (April 8, 1976). See also, e.g., 81 

FR 71910 (Oct. 18, 2016) for a description of the 

history of the listing decision for lead under CAA 

section 108. 

205 73 FR 66965 (Nov. 12, 2008). 

206 81 FR 71912–71913 (Oct. 18, 2016). 

207 Documents pertaining to the current review of 

the NAAQS for Lead can be found here: https://

www.epa.gov/naaqs/lead-pb-air-quality-standards. 

208The EPA released the ISA for Lead, External 

Review Draft, as part of the Agency’s current review 

of the science regarding health and welfare effects 

of lead. EPA/600/R–23/061. This draft assessment 

is undergoing peer review by the Clean Air 

Scientific Advisory Committee (CASAC) and public 

comment, and is available at: https://cfpub.epa.gov/ 

ncea/isa/recordisplay.cfm?deid=357282. 

209 77 FR 555 (Jan. 5, 2012). 

210 78 FR 9112 (Feb. 7, 2013). 

211 88 FR 11556 (Feb. 23, 2023). 

and their implications discussed in 

Kamal et al. (2022).199

The data summarized in this section 

indicate that there is a greater 

prevalence of children under five years 

of age, an at-risk population for lead 

effects, within 500 meters or one 

kilometer of some airports compared to 

more distant locations. This information 

also indicates that there is a greater 

prevalence of people of color and of 

low-income populations within 500 

meters or one kilometer of some airports 

compared with people living more 

distant. If such differences were to 

contribute to disproportionate and 

adverse impacts on particular 

communities, they could indicate an EJ 

concern. Given the number of children 

in close proximity to runways, 

including those in communities with EJ 

concerns, there is a potential for 

substantial implications for children’s 

health, depending on lead exposure 

levels and associated risk. 

Some commenters on the proposed 

findings expressed concern that 

communities in close proximity to 

general aviation airports are often lowincome communities and communities 

of color who are disproportionately 

burdened by lead exposure.200 Some 

commenters also noted that children 

who attend school near airports may 

experience higher levels of exposure 

compared with children who attend 

school more distant from an airport, and 

they cite recent research reporting 

higher blood lead levels in children who 

attend school near one highly active 

general aviation airport.201 The EPA 

responds to these comments in the 

Response to Comments document for 

this action. 

B. Federal Actions To Reduce Lead 

Exposure 

The Federal Government has a 

longstanding commitment to programs 

to reduce exposure to lead, particularly 

for children. In December 2018, the 

President’s Task Force on 

Environmental Health Risks and Safety 

Risks to Children released the Federal 

Action Plan to Reduce Childhood Lead 

Exposures and Associated Health 

Impacts (Federal Lead Action Plan), 

detailing the Federal Government’s 

commitments and actions to reduce lead 

exposure in children, some of which are 

described in this section.202 Building on 

the 2018 Federal Lead Action Plan, in 

October 2022, the EPA finalized its 

Strategy to Reduce Lead Exposures and 

Disparities in U.S. Communities (Lead 

Strategy).203 The Lead Strategy 

describes the EPA-wide and 

government-wide approaches to 

strengthen public health protections, 

address legacy lead contamination for 

communities with the greatest 

exposures, and promote environmental 

justice. In this section, we describe 

some of the EPA’s actions to reduce lead 

exposures from air, water, lead-based 

paint, and contaminated sites. 

In 1976, the EPA listed lead under 

CAA section 108, making it what is 

called a ‘‘criteria air pollutant.’’ 204 Once 

lead was listed, the EPA issued primary 

and secondary NAAQS under sections 

109(b)(1) and (2), respectively. The EPA 

issued the first NAAQS for lead in 1978 

and revised the lead NAAQS in 2008 by 

reducing the level of the standard from 

1.5 micrograms per cubic meter to 0.15 

micrograms per cubic meter and 

revising the averaging time and form to 

an average over a consecutive threemonth period, as described in 40 CFR 

50.16.205 The EPA’s 2016 Federal 

Register document describes the 

Agency’s decision to retain the existing 

Lead NAAQS.206 The Lead NAAQS is 

currently undergoing review.207 208

States are primarily responsible for 

ensuring attainment and maintenance of 

the NAAQS. Under section 110 of the 

Act and related provisions, states are to 

submit, for the EPA’s review and, if 

appropriate, approval, state 

implementation plans that provide for 

the attainment and maintenance of such 

standards through control programs 

directed to sources of the pollutants 

involved. 

Additional EPA programs to address 

lead in the environment include the 

prohibition on gasoline containing lead 

or lead additives for highway use under 

section 211 of the Act; the new source 

performance standards under section 

111 of the Act; and emissions standards 

for solid waste incineration units and 

the national emission standards for 

hazardous air pollutants (NESHAP) 

under sections 129 and 112 of the Act, 

respectively. 

The EPA has taken a number of 

actions associated with these air 

pollution control programs, including 

completion of several regulations 

requiring reductions in lead emissions 

from stationary sources regulated under 

the CAA sections 111, 112 and 129. For 

example, in January 2012, the EPA 

updated the NESHAP for the secondary 

lead smelting source category.209 These 

amendments to the original maximum 

achievable control technology standards 

apply to facilities nationwide that use 

furnaces to recover lead from leadbearing scrap, mainly from automobile 

batteries. Regulations completed in 2013 

for commercial and industrial solid 

waste incineration units also require 

reductions in lead emissions.210 In 

February 2023, the EPA finalized 

amendments to the NSPS (as a new 

subpart) and the Area Source NESHAP 

for the Lead Acid Battery Manufacturing 

source category.211 The amendments to 

the standards for affected processes 

including grid casting, lead reclamation, 

and paste mixing operations at lead acid 

battery facilities will result in 

reductions in lead emissions and 

improvements in compliance assurance 

measures. 

A broad range of Federal programs 

beyond those that focus on air pollution 

control provide for nationwide 

reductions in environmental releases 

and human exposures to lead. For 

example, pursuant to section 1417 of the 

Safe Drinking Water Act (SDWA), any 

pipe, pipe or plumbing fitting or fixture, 

solder, or flux may not be used in new 

installations or repairs of any public 

water system or plumbing in a 


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212Effective in Jan. 2014, the amount of lead 

permitted in pipes, fittings, and fixtures was 

lowered. See, section 1417 of the Safe Drinking 

Water Act: Prohibition on Use of Lead Pipes, 

Solder, and Flux at https://www.epa.gov/sdwa/uselead-free-pipes-fittings-fixtures-solder-and-fluxdrinking-water. 213 40 CFR part 141, subpart I (June 7, 1991). 214 40 CFR part 141, subpart I (June 7, 1991). 215 86 FR 4198. (Jan. 15, 2021). 

216E.O. 13990. Protecting Public Health and the 

Environment and Restoring Science to Tackle the 

Climate Crisis. 86 FR 7037 (Jan. 20, 2021). 

217 86 FR 31939 (Dec. 17, 2021). 

218See https://www.epa.gov/ground-water-anddrinking-water/review-national-primary-drinkingwater-regulation-lead-and-copper. Accessed on 

Nov. 30, 2021. 

219 86 FR 31939 (Dec. 17, 2021). 

220 66 FR 1206 (Jan. 5, 2001). 

221 84 FR 32632 (July 9, 2019). 

222 86 FR 983 (Jan. 7, 2021). 

223 86 FR 7037 (Jan. 20, 2021). 

residential or non-residential facility 

providing water for human 

consumption or introduced into 

commerce (except uses for 

manufacturing or industrial purposes) 

unless it is considered ‘‘lead free’’ as 

defined by that Act.212 The EPA’s Lead 

and Copper Rule,213 first promulgated 

in 1991, regulates lead in public 

drinking water systems through a 

treatment technique that requires water 

systems to monitor drinking water at 

customer taps and, if an action level is 

exceeded, undertake a number of 

actions including those to control 

corrosion to minimize lead exposure.214

On January 15, 2021, the agency 

published the most recent revisions, the 

Lead and Copper Rule Revisions 

(LCRR),215 and subsequently reviewed 

the rule in accordance with Executive 

Order 13990.216 While the LCRR took 

effect in December 2021, the agency 

concluded that there are significant 

opportunities to improve the LCRR.217

The EPA is developing a new proposed 

rule, the Lead and Copper Rule 

Improvements (LCRI),218 to further 

strengthen the lead drinking water 

regulations. The EPA identified priority 

improvements for the LCRI: proactive 

and equitable lead service line 

replacement (LSLR), strengthening 

compliance tap sampling to better 

identify communities most at risk of 

lead in drinking water and to compel 

lead reduction actions, and reducing the 

complexity of the regulation through 

improvement of the action and trigger 

level construct.219 The EPA intends to 

propose and promulgate the LCRI prior 

to October 16, 2024. 

While the EPA continues to improve 

regulatory actions to reduce lead 

exposure in drinking water, the EPA 

recognizes that directly assisting states 

and communities and providing 

dedicated funding provided in the 

Bipartisan Infrastructure Law for lead 

service line identification and 

replacement of full lead service lines 

(LSLs) is also important in safeguarding 

public health. The EPA is providing $15 

billion through the Drinking Water State 

Revolving Fund (DWSRF) dedicated 

exclusively to lead service line 

identification and replacement. In 

addition, $11.7 billion in DWSRF 

general supplemental funding, provided 

by the Bipartisan Infrastructure Law, is 

going to projects to improve drinking 

water quality, including those to reduce 

lead in drinking water. For this funding, 

states are required to provide 49% as 

additional subsidization in the form of 

principal forgiveness and/or grants. 

States must provide additional 

subsidization to water systems that meet 

the state’s disadvantaged community 

criteria as described in section 1452(d) 

of SDWA, furthering the objectives of 

the Justice40 Initiative. In October 2022, 

the EPA announced projects selected to 

receive over $30 million in grant 

funding that will help communities and 

schools address lead in drinking water 

and remove lead pipes across the 

country in underserved and other 

disadvantaged communities through the 

Water Infrastructure Improvements for 

the Nation Act’s Reducing Lead in 

Drinking Water grant program. The EPA 

recently announced the Lead Service 

Line Replacement Accelerators 

initiative which will provide targeted 

technical assistance to communities in 

Connecticut, Pennsylvania, New Jersey, 

and Wisconsin to support expanded 

access to funding and to accelerate lead 

pipe replacement. While the EPA is 

focusing initial efforts in four states, the 

Agency anticipates this work will serve 

as a roadmap for additional lead service 

line replacement efforts across the 

nation in the future. 

Federal programs to reduce exposure 

to lead in paint, dust, and soil are 

specified under the comprehensive 

Federal regulatory framework developed 

under the Residential Lead-Based Paint 

Hazard Reduction Act (Title X). Under 

Title X (codified, in part, as Title IV of 

the Toxic Substances Control Act 

[TSCA]), the EPA has established 

regulations and associated programs in 

six categories: (1) Training, certification 

and work practice requirements for 

persons engaged in lead-based paint 

activities (abatement, inspection and 

risk assessment); accreditation of 

training providers; and authorization of 

state and Tribal lead-based paint 

programs; (2) training, certification, and 

work practice requirements for persons 

engaged in home renovation, repair and 

painting (RRP) activities; accreditation 

of RRP training providers; and 

authorization of state and Tribal RRP 

programs; (3) ensuring that, for most 

housing constructed before 1978, 

information about lead-based paint and 

lead-based paint hazards flows from 

sellers to purchasers, from landlords to 

tenants, and from renovators to owners 

and occupants; (4) establishing 

standards for identifying dangerous 

levels of lead in paint, dust and soil; (5) 

providing grant funding to establish and 

maintain state and Tribal lead-based 

paint programs; and (6) providing 

information on lead hazards to the 

public, including steps that people can 

take to protect themselves and their 

families from lead-based paint hazards. 

The most recent rules issued under 

Title IV of TSCA revised the dust-lead 

hazard standards (DLHS) and dust-lead 

clearance levels (DLCL) which were 

established in a 2001 final rule entitled 

‘‘Identification of Dangerous Levels of 

Lead.’’ 220 The DLHS are incorporated 

into the requirements and risk 

assessment work practice standards in 

the EPA’s Lead-Based Paint Activities 

Rule, codified at 40 CFR part 745, 

subpart L. They provide the basis for 

risk assessors to determine whether 

dust-lead hazards are present in target 

housing (i.e., most pre-1978 housing) 

and child-occupied facilities (pre-1978 

nonresidential properties where 

children 6 years of age or under spend 

a significant amount of time such as 

daycare centers and kindergartens). If 

dust-lead hazards are present, the risk 

assessor will identify acceptable options 

for controlling the hazards in the 

respective property, which may include 

abatements and/or interim controls. In 

July 2019, the EPA published a final 

rule revising the DLHS from 40 

micrograms per square foot and 250 

micrograms per square foot to 10 

micrograms per square foot and 100 

micrograms per square foot of lead in 

dust on floors and windowsills, 

respectively.221 The DLCL are used to 

evaluate the effectiveness of a cleaning 

following an abatement. If the dust-lead 

levels are not below the clearance 

levels, the components (i.e., floors, 

windowsills, troughs) represented by 

the failed sample(s) shall be recleaned 

and retested. In January 2021, the EPA 

published a final rule revising the DLCL 

to match the DLHS, lowering them from 

40 micrograms per square foot and 250 

micrograms per square foot to 10 

micrograms per square foot and 100 

micrograms per square foot on floors 

and windowsills, respectively.222 The 

EPA is now reconsidering the 2019 and 

2021 rules in accordance with Executive 

Order 13990 223 and in response to a 


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224 88 FR 50444 (August 1, 2023). 

225For more information about the EPA’s 

CERCLA program, see https://www.epa.gov/ 

superfund. 

226For more information about the EPA’s RCRA 

program, see https://www.epa.gov/rcra. 

227See https://www.epa.gov/regulationsemissions-vehicles-and-engines/petitions-and-eparesponse-memorandums-related-lead. 

228 87 FR 62772 (Oct. 17, 2022). 

229The 2021 petition is available at https://

www.epa.gov/system/files/documents/2022-01/ 

aviation-leaded-avgas-petition-exhibits-final-2021- 

10-12.pdf. 

230EPA’s response to the 2021 petition is 

available at https://www.epa.gov/system/files/ 

documents/2022-01/ltr-response-aircraft-leadpetitions-aug-oct-2022-01-12.pdf. 

231 81 FR 54422–54475 (Aug. 15, 2016). 

232See e.g., 81 FR 55434–54440 (Aug. 15, 2016). 

233 74 FR 66505–66510 (Dec. 15, 2009). 

234Coalition for Responsible Regulation, Inc. v. 

EPA, 684 F.3d 102 (D.C. Cir. 2012) (CRR) (rev’d in 

part on other grounds sub nom. Utility Air 

Regulatory Group v. EPA, 573 U.S. 302 (2014)). As 

discussed in greater detail in the 2016 Findings, the 

Supreme Court granted some of the petitions for 

certiorari that were filed on CRR, while denying 

others, but agreed to decide only the question: 

‘‘Whether EPA permissibly determined that its 

regulation of greenhouse gas emissions from new 

motor vehicles triggered permitting requirements 

under the Clean Air Act for stationary sources that 

emit greenhouse gases.’’ 81 FR 54422, 54442 (Aug. 

15, 2016). Thus, the Supreme Court did not disturb 

the D.C. Circuit’s holding in CRR that affirmed the 

2009 Endangerment Finding. 

235For example, the text in CAA section 202(a) 

that was the basis for the 2009 Findings addresses 

‘‘the emission of any air pollutant from any class 

or classes of new motor vehicles or new motor 

vehicle engines, which in [the Administrator’s] 

judgment cause, or contribute to, air pollution 

which may reasonably be anticipated to endanger 

public health or welfare.’’ Similarly, section 

231(a)(2)(A) concerns ‘‘the emission of any air 

pollutant from any class or classes of aircraft 

engines which in [the Administrator’s] judgment 

causes, or contributes to, air pollution which may 

reasonably be anticipated to endanger public health 

or welfare.’’ Additional discussion of the parallels 

in the statutory text and legislative history between 

CAA section 202(a) and 231(a)(2)(A) can be found 

in the 2016 Findings. See 81 FR 55434—55437 

(Aug. 15, 2016). 

236 81 FR 55434 (Aug. 15, 2016). 

237 81 FR 55434 (Aug. 15, 2016). 

May 2021 decision by U.S. Court of 

Appeals for the Ninth Circuit. In August 

2023, EPA proposed updating the DLHS 

and DLCL again.224 If finalized as 

proposed, the DLHS for floors and 

window sills would be any reportable 

level greater than zero, as analyzed by 

any laboratory recognized by EPA’s 

National Lead Laboratory Accreditation 

Program. The new DLCL would be 3 

micrograms per square foot (mg/ft2) for 

floors, 20 mg/ft2 for window sills and 25 

mg/ft2 for window troughs. 

Programs associated with the 

Comprehensive Environmental 

Response, Compensation, and Liability 

Act (CERCLA or Superfund) 225 and 

Resource Conservation Recovery Act 

(RCRA) 226 also implement removal and 

remedial response programs that reduce 

or abate exposures to releases or 

threatened releases of lead and other 

hazardous substances. Furthermore, 

CERCLA section 104(a)(1) authorizes the 

EPA and other Federal agencies to 

respond to releases or threatened 

releases of pollutants or contaminants 

when the release, or potential release, 

may present an imminent and 

substantial danger to the public health 

or welfare. In addition, CERCLA section 

104(a)(1) and the National Oil and 

Hazardous Substances Pollution 

Contingency Plan (NCP) authorize 

remedial investigations (e.g., 

monitoring, testing, information 

collection) and removal actions for 

hazardous substances, pollutants, or 

contaminants. 

The EPA develops and implements 

protective levels for lead in soil (and 

other media when appropriate) at 

Superfund sites and, together with 

states, at RCRA corrective action 

facilities. The Office of Land and 

Emergency Management develops 

policy and guidance for addressing 

multimedia lead contamination and 

determining appropriate response 

actions at lead-contaminated sites. 

Federal programs, including those 

implementing RCRA, provide for 

management of hazardous substances 

such as lead in hazardous and 

municipal solid waste (e.g., 50 FR 

28702, July 15, 1985; 52 FR 45788, 

December 1, 1987). 

C. Lead Endangerment Petitions for 

Rulemaking and the EPA Responses 

The Administrator’s final findings 

further respond to several citizen 

petitions on this subject, including the 

following: petition for rulemaking 

submitted by Friends of the Earth in 

2006, petition for rulemaking submitted 

by Friends of the Earth, Oregon Aviation 

Watch and Physicians for Social 

Responsibility in 2012, petition for 

reconsideration submitted by Friends of 

the Earth, Oregon Aviation Watch, and 

Physicians for Social Responsibility in 

2014, and petition for rulemaking from 

Alaska Community Action on Toxics, 

Center for Environmental Health, 

Friends of the Earth, Montgomery-Gibbs 

Environmental Coalition, Oregon 

Aviation Watch, the County of Santa 

Clara, CA, and the Town of Middleton, 

WI, in 2021. These petitions and the 

EPA’s responses are described more 

fully in the proposal for this 

action.227 228

In the most recent of these petitions, 

submitted in 2021, Alaska Community 

Action on Toxics, Center for 

Environmental Health, Friends of the 

Earth, Montgomery-Gibbs 

Environmental Coalition, Oregon 

Aviation Watch, the County of Santa 

Clara, CA, and the Town of Middleton, 

WI, again petitioned the EPA to conduct 

a proceeding under CAA section 231 

regarding whether lead emissions from 

piston-engine aircraft cause or 

contribute to air pollution that may 

reasonably be anticipated to endanger 

public health or welfare.229 The EPA 

responded in 2022 noting our intent to 

develop a proposal under CAA section 

231(a)(2)(A) regarding whether lead 

emissions from piston-engine aircraft 

cause or contribute to air pollution that 

may reasonably be anticipated to 

endanger public health or welfare, and, 

after evaluating public comments on the 

proposal, issue any final determination 

in 2023, as the Agency is doing in this 

action.230

III. Legal Framework for This Action 

In this action, the EPA is finalizing 

two separate determinations—an 

endangerment finding and a cause or 

contribute finding—under section 

231(a)(2)(A) of the Clean Air Act. The 

EPA has, most recently, finalized such 

findings under CAA section 231 for 

greenhouse gases (GHGs) in 2016 (2016 

Findings), and in that action the EPA 

provided a detailed explanation of the 

legal framework for making such 

findings and the statutory 

interpretations and caselaw supporting 

its approach.231 In this final action, the 

Administrator used the same approach 

of applying a two-part test under section 

231(a)(2)(A) as described in the 2016 

Findings and relied on the same 

interpretations supporting that 

approach, which are briefly described in 

this section, and set forth in greater 

detail in the 2016 Findings.232 This is 

also the same approach that the EPA 

used in making endangerment and 

cause or contribute findings for GHGs 

under section 202(a) of the CAA in 2009 

(2009 Findings),233 which was affirmed 

by the U.S. Court of Appeals for the D.C. 

Circuit in 2012.234 As explained further 

in the 2016 Findings, the text of the 

CAA section 231(a)(2)(A), which 

concerns aircraft emissions, mirrors the 

text of CAA section 202(a), which 

concerns motor vehicle emissions and 

which was the basis for the 2009 

Findings.235 236 Accordingly, for the 

same reasons as discussed in the 2016 

Findings, the EPA believes it is 

reasonable to use the same approach 

under section 231(a)(2)(A)’s similar text 

as was used under section 202(a) for the 

2009 Findings, and it is acting 

consistently with that framework for 

purposes of these final findings under 

section 231.237 As this approach has 


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238Regarding ‘‘welfare,’’ the CAA states that ‘‘[a]ll 

language referring to effects on welfare includes, 

but is not limited to, effects on soils, water, crops, 

vegetation, manmade materials, animals, wildlife, 

weather, visibility, and climate, damage to and 

deterioration of property, and hazards to 

transportation, as well as effects on economic 

values and on personal comfort and well-being, 

whether caused by transformation, conversion, or 

combination with other air pollutants.’’ CAA 

section 302(h). Regarding ‘‘public health,’’ there is 

no definition of ‘‘public health’’ in the Clean Air 

Act. The Supreme Court has discussed the concept 

of ‘‘public health’’ in the context of whether costs 

can be considered when setting NAAQS. Whitman 

v. American Trucking Ass’n, 531 U.S. 457 (2001). 

In Whitman, the Court imbued the term with its 

most natural meaning: ‘‘the health of the public.’’ 

Id. at 466. 

239See Massachusetts v. EPA, 549 U.S. 497, 533 

(2007) (interpreting an analogous provision in CAA 

section 202). 

240See 81 FR 54435 (Aug. 15, 2016). 

241CRR, 684 F.3d at 122 (internal citations 

omitted) (June 26, 2012). 

242CRR, 684 F.3d at 122 (internal citations 

omitted) (June 26, 2012). 

243 81 FR 54425 (Aug. 15, 2016). 

244See, e.g., Rulemaking for non-road 

compression-ignition engines under section 

213(a)(4) of the CAA, Proposed Rule at 58 FR 

28809, 28813–14 (May 17, 1993), Final Rule at 59 

FR 31306, 31318 (June 17, 1994); Rulemaking for 

highway heavy-duty diesel engines and diesel 

sulfur fuel under sections 202(a) and 211(c) of the 

CAA, Proposed Rule at 65 FR 35430 (June 2, 2000), 

and Final Rule at 66 FR 5002 (Jan. 18, 2001). 

245 87 FR 62773–62774 (Oct. 17, 2022). 

246As the Administrator is applying the 

provisions of CAA section 307(d) to this action 

under section 307(d)(1)(V), we need not determine 

whether those provisions would apply to this action 

under section 307(d)(1)(F). 

247See CRR, 684 F.3d at 117 (explaining two-part 

analysis under section 202(a)) (June 26, 2012). 

been previously discussed at length in 

the 2016 Findings, as well as in the 

2009 Findings, the EPA provides only a 

brief description in this final action. 

A. Statutory Text and Basis for This 

Action 

Section 231(a)(2)(A) of the CAA 

provides that the ‘‘Administrator shall, 

from time to time, issue proposed 

emission standards applicable to the 

emission of any air pollutant from any 

class or classes of aircraft engines which 

in his judgment causes, or contributes 

to, air pollution which may reasonably 

be anticipated to endanger public health 

or welfare.’’ 238 In this action, the EPA 

is addressing the predicate for 

regulatory action under CAA section 

231 through a two-part test, which as 

noted previously, is the same as the test 

used in the 2016 Findings under section 

231 and in the 2009 Findings under 

section 202 of the CAA. 

As the first step of the two-part test, 

the Administrator must decide whether, 

in his judgment, the air pollution under 

consideration may reasonably be 

anticipated to endanger public health or 

welfare. As the second step, the 

Administrator must decide whether, in 

his judgment, emissions of an air 

pollutant from certain classes of aircraft 

engines cause or contribute to this air 

pollution. If the Administrator answers 

both questions in the affirmative, he 

will issue standards under section 

231.239

In accordance with the EPA’s 

interpretation of the text of section 

231(a)(2)(A), as described in the 2016 

Findings, the phrase ‘‘may reasonably 

be anticipated’’ and the term 

‘‘endanger’’ in section 231(a)(2)(A) 

authorize, if not require, the 

Administrator to act to prevent harm 

and to act in conditions of 

uncertainty.240 They do not limit him to 

merely reacting to harm or to acting 

only when certainty has been achieved; 

indeed, the references to anticipation 

and to endangerment imply that the 

failure to look to the future or to less 

than certain risks would be to abjure the 

Administrator’s statutory 

responsibilities. As the D.C. Circuit 

explained, the language ‘‘may 

reasonably be anticipated to endanger 

public health or welfare’’ in CAA 

section 202(a) requires a ‘‘precautionary, 

forward-looking scientific judgment 

about the risks of a particular air 

pollutant, consistent with the CAA’s 

precautionary and preventive 

orientation.’’ 241 The court determined 

that ‘‘[r]equiring that the EPA find 

‘certain’ endangerment of public health 

or welfare before regulating greenhouse 

gases would effectively prevent the EPA 

from doing the job that Congress gave it 

in [section] 202(a)—utilizing emission 

standards to prevent reasonably 

anticipated endangerment from 

maturing into concrete harm.’’ 242 The 

same language appears in section 

231(a)(2)(A), and the same 

interpretation applies in that context. 

Moreover, by instructing the 

Administrator to consider whether 

emissions of an air pollutant cause or 

contribute to air pollution in the second 

part of the two-part test, the Act makes 

clear that he need not find that 

emissions from any one sector or class 

of sources are the sole or even the major 

part of the air pollution considered. 

This is clearly indicated by the use of 

the term ‘‘contribute.’’ Further, the 

phrase ‘‘in his judgment’’ authorizes the 

Administrator to weigh risks and to 

consider projections of future 

possibilities, while also recognizing 

uncertainties and extrapolating from 

existing data. 

Finally, when exercising his judgment 

in making both the endangerment and 

cause-or-contribute findings, the 

Administrator balances the likelihood 

and severity of effects. Notably, the 

phrase ‘‘in his judgment’’ modifies both 

‘‘may reasonably be anticipated’’ and 

‘‘cause or contribute.’’ 

Often, past endangerment and cause 

or contribute findings have been 

proposed concurrently with proposed 

standards under various sections of the 

CAA, including section 231.243

Comment has been taken on these 

proposed findings as part of the notice 

and comment process for the emission 

standards.244 However, there is no 

requirement that the Administrator 

propose or finalize the endangerment 

and cause or contribute findings 

concurrently with proposed standards 

and, most recently under section 231, 

the EPA made endangerment and cause 

or contribute findings for GHGs separate 

from, and prior to, proceeding to set 

standards. 

As noted in the proposal,245 the 

Administrator is applying the 

procedural provisions of CAA section 

307(d) to this action, pursuant to CAA 

section 307(d)(1)(V), which provides 

that the provisions of 307(d) apply to 

‘‘such other actions as the Administrator 

may determine.’’ 246 Any subsequent 

standard-setting rulemaking under CAA 

section 231 would also be subject to the 

procedures under CAA section 307(d), 

as provided in CAA section 307(d)(1)(F) 

(applying the provisions of CAA section 

307(d) to the promulgation or revision 

of any aircraft emission standard under 

CAA section 231). Thus, these final 

findings are subject to the same 

procedural requirements that would 

apply if the final findings were part of 

a standard-setting rulemaking. 

B. Considerations for the Endangerment 

and Cause or Contribute Analyses 

Under Section 231(a)(2)(A) 

In the context of this final action, the 

EPA understands section 231(a)(2)(A) of 

the CAA to call for the Administrator to 

exercise his judgment and make two 

separate determinations: first, whether 

the relevant kind of air pollution (here, 

lead air pollution) may reasonably be 

anticipated to endanger public health or 

welfare, and second, whether emissions 

of any air pollutant from classes of the 

sources in question (here, any aircraft 

engine that is capable of using leaded 

aviation gasoline), cause or contribute to 

this air pollution.247

This analysis entails a scientific 

judgment by the Administrator about 

the potential risks posed by lead 

emissions to public health and welfare. 

In this final action, the EPA used the 

same approach in making scientific 

judgments regarding endangerment as it 

has previously described in the 2016 


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248See, e.g., 81 FR 54434–55435 (Aug. 15, 2016). 

249See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 

250See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 

251See, e.g., 81 FR 54437–54438 (Aug. 15, 2016). 

252See 81 FR 54437–54438 (Aug. 15, 2016). 

253See 81 FR 54437–54438 (Aug. 15, 2016). 

254See 81 FR 54437–54438 (Aug. 15, 2016). 

255CRR, 684 F.3d at 122–123 (June 26, 2012). 

256CRR, 684 F.3d at 122–123. (quoting Ethyl 

Corp., 541 F.2d at 18) (June 26, 2012). 

257 81 FR 54438 (Aug. 15, 2016). 

258 81 FR 54438 (Aug. 15, 2016). 

259 81 FR 54438 (Aug. 15, 2016). 

260See 81 FR 54462 (Aug. 15, 2016). 261CAA section 233. 

Findings, and its analysis was guided by 

the same five principles that guided the 

Administrator’s analysis in those 

Findings.248

Similarly, the EPA took the same 

approach to the cause or contribute 

analysis as was previously explained in 

the 2016 Findings.249 For example, as 

previously noted, section 231(a)(2)(A)’s 

instruction to consider whether 

emissions of an air pollutant cause or 

contribute to air pollution makes clear 

that the Administrator need not find 

that emissions from any one sector or 

class of sources are the sole or even the 

major part of an air pollution 

problem.250 Moreover, like the language 

in CAA section 202(a) that governed the 

2009 Findings, the statutory language in 

section 231(a)(2)(A) does not contain a 

modifier on its use of the term 

‘‘contribute.’’ 251 Unlike other CAA 

provisions, it does not require 

‘‘significant’’ contribution. Compare, 

e.g., CAA sections 111(b); 213(a)(2), (4). 

Congress made it clear that the 

Administrator is to exercise his 

judgment in determining contribution, 

and authorized regulatory controls to 

address air pollution even if the air 

pollution problem results from a wide 

variety of sources.252 While the 

endangerment test looks at the air 

pollution being considered as a whole 

and the risks it poses, the cause or 

contribute test is designed to authorize 

the EPA to identify and then address 

what may well be many different 

sectors, classes, or groups of sources 

that are each part of the problem.253

Moreover, as the EPA has previously 

explained, the Administrator has ample 

discretion in exercising his reasonable 

judgment and determining whether, 

under the circumstances presented, the 

cause or contribute criterion has been 

met.254 As noted in the 2016 Findings, 

in addressing provisions in section 

202(a), the D.C. Circuit has explained 

that the Act at the endangerment finding 

step did not require the EPA to identify 

a precise numerical value or ‘‘a 

minimum threshold of risk or harm 

before determining whether an air 

pollutant endangers.’’ 255 Accordingly, 

the EPA ‘‘may base an endangerment 

finding on ‘a lesser risk of greater harm 

. . . or a greater risk of lesser harm’ or 

any combination in between.’’ 256 As the 

language in section 231(a)(2)(A) is 

analogous to that in section 202(a), it is 

reasonable to apply this interpretation 

to the endangerment determination 

under section 231(a)(2)(A).257 Moreover, 

the logic underlying this interpretation 

supports the general principle that 

under CAA section 231 the EPA is not 

required to identify a specific minimum 

threshold of contribution from 

potentially subject source categories in 

determining whether their emissions 

‘‘cause or contribute’’ to the 

endangering air pollution.258 The 

reasonableness of this principle is 

further supported by the fact that 

section 231 does not impose on the EPA 

a requirement to find that such 

contribution is ‘‘significant,’’ let alone 

the sole or major cause of the 

endangering air pollution.259

Finally, as also described in the 2016 

Findings, there are a number of possible 

ways of assessing whether air pollutants 

cause or contribute to the air pollution 

which may reasonably be anticipated to 

endanger public health and welfare, and 

no single approach is required or has 

been used exclusively in previous cause 

or contribute determinations under title 

II of the CAA.260

C. Regulatory Authority for Emission 

Standards 

Though the EPA is not proposing 

standards in this final action, in issuing 

these final findings, the EPA becomes 

subject to a duty under CAA section 231 

regarding emission standards applicable 

to emissions of lead from aircraft 

engines. As noted in section III.A. of 

this document, section 231(a)(2)(A) of 

the CAA directs the Administrator of 

the EPA to propose and promulgate 

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. 

CAA section 231(a)(2)(B) further 

directs the EPA to consult with the 

Administrator of the 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. CAA section 231(a)(3) provides 

that after we provide an opportunity for 

a public hearing on standards, the 

Administrator shall issue standards 

‘‘with such modifications as he deems 

appropriate.’’ In addition, under CAA 

section 231(b), the effective date of any 

standards shall provide the necessary 

time to permit the development and 

application of the requisite technology, 

giving appropriate consideration to the 

cost of compliance, as determined by 

the EPA in consultation with the U.S. 

Department of Transportation (DOT). 

Once the EPA adopts standards, CAA 

section 232 then directs the Secretary of 

DOT to prescribe regulations to ensure 

compliance with the EPA’s standards. 

Finally, section 233 of the CAA 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.261

D. Response to Certain Comments on 

the Legal Framework for This Action 

In commenting on the legal 

framework for this action, some 

commenters assert that the EPA does 

have authority under CAA section 

231(a)(2)(A) to both find that lead air 

pollution may reasonably be anticipated 

to endanger the public health and 

welfare and to find that engine 

emissions of lead from certain aircraft 

cause or contribute to the lead air 

pollution that may reasonably be 

anticipated to endanger the public 

health and welfare. We agree with these 

comments. 

Other commenters assert that the EPA 

does not have the legal authority to 

proceed with this proposal or regulate 

aviation fuel. These commenters state 

that Congress excluded aircraft from the 

CAA of 1970, that the EPA does not 

have authority to regulate aircraft fuel 

(citing a regulatory definition of 

‘‘transportation fuel’’ in 40 CFR 

80.1401) and that aircraft are not motor 

vehicles (citing a regulatory definition 

of ‘‘motor vehicles’’ in 40 CFR 85.1703). 

These commenters say that the 

definitions of transportation fuel and 

motor vehicles were not changed 

through 1977 or 1990 amendments to 

the CAA. Additionally, commenters 

assert that the ‘‘EPA points to findings 

for Green House Gases (GHGs) under 

section 202(a) supportive of its 

proposed authority,’’ quoting that 

section and emphasizing the terms 

‘‘new motor vehicles’’ and ‘‘new motor 

vehicle engines’’ which are used in it. 

In response, the EPA notes that these 

commenters have fundamentally 

misunderstood the nature of this action 

and the legal authority upon which it 

relies. These final findings do not 


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262The change to the current language in section 

231(a)(2) occurred in 1977, see Clean Air Act 

Amendments of 1977, Public Law 95–95, 91 Stat. 

685, 791 (1977). 

263See e.g., 81 FR 55434–54440 (Aug. 15, 2016). 

264 74 FR 66496, 66505–10 (Dec. 15, 2009); see 

also Coalition for Responsible Regulation, Inc. v. 

EPA, 684 F.3d 102 (D.C. Cir. 2012) (CRR) 

(subsequent history omitted) (affirming EPA’s 

approach in the 2009 Findings). 

establish regulatory standards for leaded 

avgas, nor are they related in any way 

to the regulatory definitions of 

transportation fuels in 40 CFR 80.1401 

or of motor vehicles in 40 CFR 85.1703, 

which implement EPA programs under 

Part A of Title II of the CAA and do not 

apply to aircraft that are governed by 

Part B of Title II. EPA’s regulatory 

provisions implementing Title II Part B 

and related to air pollution from aircraft 

are found in 40 CFR parts 87, 1030, and 

1031. The EPA’s authority for this 

action is not based on its authority to 

regulate fuels under CAA section 211 or 

its authority to regulate motor vehicles 

or motor vehicle engines under CAA 

section 202(a). Rather, the EPA’s 

authority for this action comes from 

CAA section 231(a)(2). Further, this 

action is focused on the threshold 

endangerment and cause or contribute 

criteria, which are being undertaken in 

proceedings that are separate and 

distinct from any follow-on regulatory 

action; no regulatory provisions were 

proposed and none are being finalized 

in this action. 

In response to the claims that aircraft 

are excluded from the CAA and that the 

EPA does not have authority to conduct 

this endangerment and cause or 

contribute finding, we disagree. As 

described in the proposal, the EPA is 

acting under the express authority 

prescribed by Congress in section 

231(a)(2)(A) of the CAA, which, as 

amended, provides that the 

Administrator ‘‘shall, from time to time, 

issue proposed emission standards 

applicable to the emission of any air 

pollutant from any class or classes of 

aircraft engines which in his judgment 

causes, or contributes to, air pollution 

which may reasonably be anticipated to 

endanger public health or welfare.’’ The 

D.C. Circuit recognized EPA’s authority 

to promulgate emission standards 

applicable to air pollutants from aircraft 

engines under CAA section 231 in 

National Association of Clean Air 

Agencies v. EPA, 489 F.3d 1221 (D.C. 

Cir. 2007) (‘‘NACAA’’). Similarly, in the 

1970 amendments to the CAA, section 

231(a)(2) provided that the 

Administrator ‘‘shall issue proposed 

emission standards applicable to 

emissions of any air pollutant from any 

class or classes of aircraft or aircraft 

engines which in his judgment cause or 

contribute to or are likely to cause or 

contribute to air pollution which 

endangers the public health or welfare.’’ 

Public Law 91–604. Thus, the statement 

in the comment that the 1970 CAA 

excluded aircraft is incorrect.262

Further, the EPA has previously made 

endangerment and cause or contribute 

findings related to emissions from 

aircraft engines under section 231 of the 

CAA. 

As explained in the proposal, and in 

section III. above, in this action the 

Administrator is using the same 

approach of applying a two-part test 

under section 231(a)(2)(A) as described 

in the finalized endangerment and cause 

or contribute findings under CAA 

section 231 for greenhouse gases (GHGs) 

emissions from aircraft in 2016.263 We 

further explained that this approach is 

the same approach that the EPA used in 

making endangerment and cause and 

contribute findings for GHGs under 

section 202(a) of the CAA in 2009 (2009 

Findings), which is reasonable in light 

of the parallels of the language and 

structure between sections 231(a)(2)(A) 

and 202(a)(1) of the CAA.264 Some 

comments misconstrued EPA’s 

discussion of section 202(a) in the 

proposal to infer that EPA was relying 

on its authority under section 202(a) in 

this action. That is not the case. While 

using the same approach as in the 2009 

Findings, the EPA is not acting under 

the authority of section 202(a) in making 

these final findings, but rather, is 

relying on the authority under section 

231(a)(2)(A) as described herein, which 

expressly authorizes regulation of 

emissions of air pollutants from aircraft 

engines which the Administrator judges 

to cause or contribute to air pollution 

which may reasonably be anticipated to 

endanger public health or welfare. 

Additional commenters state that they 

are opposed to any rulemaking that 

could lead to the elimination of leaded 

avgas before a comparatively priced 

substitute fuel is available for 

widespread use. As an initial matter, the 

EPA notes that, as described in section 

III.A. of this document, in this action, 

the EPA is addressing the predicate to 

regulatory action under CAA section 

231 through a two-part test. In the first 

step of the two-part test, the 

Administrator must decide whether, in 

his judgment, the air pollution under 

consideration may reasonably be 

anticipated to endanger public health or 

welfare. As the second step, the 

Administrator must decide whether, in 

his judgment, emissions of an air 

pollutant from certain classes of aircraft 

engines cause or contribute to this air 

pollution. If the Administrator answers 

both questions in the affirmative, as he 

is doing here, the EPA becomes subject 

to a duty to propose and promulgate 

standards under section 231, but the 

EPA is not proposing or promulgating 

any standards in this action. These 

commenters have concerns regarding 

the cost and availability of unleaded 

fuels that might be required to meet a 

future emission standard for lead. To 

reiterate, the EPA is not proposing or 

promulgating any standards in this 

action, nor is the EPA reaching any 

conclusions about the possible 

elimination of leaded avgas or the cost 

or availability of comparatively priced 

substitute fuels; those issues will be 

addressed, if at all, only in a future 

standard-setting rulemaking. As for 

future standards, the delegation of 

authority in CAA section 231 to the EPA 

‘‘is both explicit and extraordinarily 

broad,’’ NACAA, 489 F.3d at 1229, and 

‘‘confer[s] broad discretion to the [EPA] 

Administrator to weigh various factors 

in arriving at appropriate standards,’’ id. 

at 1230. However, as described in 

section III.C. of this document, CAA 

section 231(a)(2)(B) directs the EPA to 

consult with the Administrator of the 

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. Further, under 

CAA section 231(b), the effective date of 

any standards shall provide the 

necessary time to permit the 

development and application of the 

requisite technology, giving appropriate 

consideration to the cost of compliance, 

as determined by the EPA in 

consultation with the U.S. Department 

of Transportation (DOT). 

IV. The Final Endangerment Finding 

Under CAA Section 231 

In this action, the Administrator finds 

that lead air pollution may reasonably 

be anticipated to endanger the public 

health and welfare within the meaning 

of CAA section 231(a)(2)(A). This 

section discusses both the public health 

and welfare aspects of the 

endangerment finding and describes the 

scientific evidence that informs the 

Administrator’s final determination. 

The vast majority of comments 

supported the EPA’s proposal and 

agreed with the EPA’s description of the 

health and welfare effects of lead air 

pollution. The Agency’s responses to 

public comments on the proposed 

endangerment finding, including those 

opposing finalizing the finding, can be 


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265EPA (2013) ISA for Lead. Section 2.2. 

‘‘Sources of Atmospheric Pb.’’ p. 2–1. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

266EPA (2013) ISA for Lead. Executive Summary. 

‘‘Sources, Fate and Transport of Lead in the 

Environment, and the Resulting Human Exposure 

and Dose.’’ pp. lxxviii-lxxix. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

267The lead air pollution can occur as elemental 

lead or in lead-containing compounds, and this 

definition of the air pollution recognizes that lead 

in air (whatever form it is found in, including in 

inorganic and organic compounds containing lead) 

has the potential to elicit public health and welfare 

effects. We note, for example, that the 2013 Lead 

ISA and 2008 AQCD described the toxicokinetics of 

inorganic and organic forms of lead and studies 

evaluating lead-related health effects commonly 

measure total lead level (i.e., all forms of lead in 

various biomarker tissues such as blood). 

268EPA (2013) ISA for Lead. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

269EPA (2006) Air Quality Criteria for Lead. EPA, 

Washington, DC, EPA/600/R–5/144aF, 2006. 

270EPA (2013) ISA for Lead. Section 5.4. 

‘‘Summary.’’ p. 5–40. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

271The causal framework draws upon the 

assessment and integration of evidence from across 

scientific disciplines, spanning atmospheric 

chemistry, exposure, dosimetry and health effects 

studies (i.e., epidemiologic, controlled human 

exposure, and animal toxicological studies), and 

assessment of the related uncertainties and 

limitations that ultimately influence our 

understanding of the evidence. This framework 

employs a five-level hierarchy that classifies the 

overall weight of evidence with respect to the 

causal nature of relationships between criteria 

pollutant exposures and health and welfare effects 

using the following categorizations: causal 

relationship; likely to be causal relationship; 

suggestive of, but not sufficient to infer, a causal 

relationship; inadequate to infer the presence or 

absence of a causal relationship; and not likely to 

be a causal relationship. EPA (2013) ISA for Lead. 

Preamble section. p. xliv. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

272EPA (2013) ISA for Lead. Table ES–1. 

‘‘Summary of causal determinations for the 

relationship between exposure to Pb and health 

effects.’’ pp. lxxxiii–lxxxvii. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

273EPA (2013) ISA for Lead. Table ES–1. 

‘‘Summary of causal determinations for the 

relationship between exposure to Pb and health 

effects.’’ p. lxxxiii and p. lxxxvi. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

274EPA (2013) ISA for Lead. Table ES–1. 

‘‘Summary of causal determinations for the 

relationship between exposure to Pb and health 

effects.’’ pp. lxxxiii–lxxxiv. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

275EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– 

lxxxviii. EPA, Washington, DC, EPA/600/R–10/ 

075F, 2013. 

found in the Response to Comments 

document for this action. After 

consideration of the comments on this 

topic, the EPA concludes that the 

scientific evidence supports finalizing 

the finding as proposed. 

A. Scientific Basis of the Endangerment 

Finding 

1. Lead Air Pollution 

Lead is emitted and exists in the 

atmosphere in a variety of forms and 

compounds and is emitted by a wide 

range of sources.265 Lead is persistent in 

the environment. Atmospheric transport 

distances of airborne lead vary 

depending on its form and particle size, 

as discussed in section II.A. of this 

document, with coarse lead-bearing 

particles deposited to a greater extent 

near the source, while fine lead-bearing 

particles can be transported long 

distances before being deposited. 

Through atmospheric deposition, lead is 

distributed to other environmental 

media, including soils and surface water 

bodies.266 Lead is retained in soils and 

sediments, where it provides a historical 

record and, depending on several 

factors, can remain available in some 

areas for extended periods for 

environmental or human exposure, with 

any associated potential public health 

and public welfare impacts. 

For purposes of this action, the EPA 

defines the ‘‘air pollution’’ referred to in 

section 231(a)(2)(A) of the CAA as lead, 

which we also refer to as lead air 

pollution in this document.267

2. Health Effects and Lead Air Pollution 

In 2013, the EPA completed the 

Integrated Science Assessment for Lead 

which built on the findings of previous 

AQCDs for Lead. These documents 

critically assess and integrate relevant 

scientific information regarding the 

health and welfare effects of lead and 

have undergone extensive critical 

review by the EPA, the Clean Air 

Scientific Advisory Committee 

(CASAC), and the public. As such, these 

assessments provide the primary 

scientific and technical basis for the 

Administrator’s finding that lead air 

pollution is reasonably anticipated to 

endanger public health and 

welfare.268 269

As summarized in section II.A. of this 

document, human exposure to lead that 

is emitted into the air can occur by 

multiple pathways. Inhalation pathways 

include both ambient air outdoors and 

ambient air that has infiltrated into 

indoor environments. Additional 

exposure pathways may involve media 

other than air, including indoor and 

outdoor dust, soil, surface water and 

sediments, vegetation and biota. The 

bioavailability of air-related lead is 

modified by several factors in the 

environment (e.g., the chemical form of 

lead, environmental fate of lead emitted 

to air). That notwithstanding, as 

described in section II.A. of this 

document, it is well-documented that 

exposures to lead emitted into the air 

can result in increased blood lead 

levels, particularly for children living 

near air lead sources, due to their 

proximity to these sources of 

exposure.270

As described in the EPA’s 2013 Lead 

ISA and in prior AQCDs, lead has been 

demonstrated to exert a broad array of 

deleterious effects on multiple organ 

systems. The 2013 Lead ISA 

characterizes the causal nature of 

relationships between lead exposure 

and health effects using a weight-ofevidence approach.271 We summarize 

here those health effects for which the 

EPA in the 2013 Lead ISA has 

concluded that the evidence supports a 

determination of either a ‘‘causal 

relationship,’’ ‘‘likely to be causal 

relationship,’’ or ‘‘suggestive of a causal 

relationship’’ between lead exposure 

and a health effect.272 In the discussion 

that follows, we summarize findings 

regarding effects observed in children, 

effects observed in adults, and 

additional effects observed that are not 

specific to an age group. 

The EPA has concluded that there is 

a ‘‘causal relationship’’ between lead 

exposure during childhood (pre and 

postnatal) and a range of health effects 

in children, including the following: 

cognitive function decrements; the 

group of externalizing behaviors 

comprising attention, increased 

impulsivity, and hyperactivity; and 

developmental effects (i.e., delayed 

pubertal onset).273 In addition, the EPA 

has concluded that the evidence 

supports a conclusion that there is a 

‘‘likely to be causal relationship’’ 

between lead exposure and conduct 

disorders in children and young adults, 

internalizing behaviors such as 

depression, anxiety and withdrawn 

behavior, auditory function decrements, 

and fine and gross motor function 

decrements.274

Multiple epidemiologic studies 

conducted in diverse populations of 

children consistently demonstrate the 

harmful effects of lead exposure on 

cognitive function (as measured by 

decrements in intelligence quotient [IQ], 

decreased academic performance, and 

poorer performance on tests of executive 

function). These findings are supported 

by extensively documented 

toxicological evidence substantiating 

the plausibility of these findings in the 

epidemiological literature and provide 

information on the likely mechanisms 

underlying these neurotoxic effects.275

Intelligence quotient is a wellestablished, and among the most 

rigorously standardized, cognitive 

function measure that has been used 

extensively as a measure of the negative 


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276EPA (2013) ISA for Lead. Section 4.3.2. 

‘‘Cognitive Function.’’ p. 4–59. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

277EPA (2006) Air Quality Criteria for Lead. 

Sections 6.2.2 and 8.4.2. EPA, Washington, DC, 

EPA/600/R–5/144aF, 2006. 

278EPA (2013) ISA for Lead. Section 4.3.2. 

‘‘Cognitive Function.’’ p. 4–59. EPA, Washington, 

DC, EPA/600/R–10/075F, 2013. 

279 In this statement, the term ‘‘concurrent’’ is 

referring to blood lead measurements that were 

taken concurrently with the neurocognitive testing. 

280EPA (2013) ISA for Lead. Section 1.9.4. ‘‘Pb 

Exposure and Neurodevelopmental Deficits in 

Children.’’ p. 1–76. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

281EPA (2013) ISA for Lead. Section 1.9.4. ‘‘Pb 

Exposure and Neurodevelopmental Deficits in 

Children.’’ p. 1–76. EPA/600/R–10/075F, 2013. 

282EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Children.’’ pp. lxxxvii– 

lxxxviii. EPA, Washington, DC, EPA/600/R–10/ 

075F, 2013. 

283EPA (2013) ISA for Lead. Section 1.9.5. 

‘‘Reversibility and Persistence of Neurotoxic Effects 

of Pb.’’ p. 1–76. EPA, Washington, DC, EPA/600/R– 

10/075F, 2013. 

284EPA (2013) ISA for Lead. Section 4.3.14. 

‘‘Public Health Significance of Associations 

between Pb Biomarkers and Neurodevelopmental 

Effects.’’ p. 4–279. EPA, Washington, DC, EPA/600/ 

R–10/075F, 2013. 

285EPA (2013) ISA for Lead. Section 1.9.1. 

‘‘Public Health Significance.’’ p. 1–68. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

286EPA (2013) ISA for Lead. Executive Summary. 

‘‘Public Health Significance.’’ p. xciii. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

287EPA (2013) ISA for Lead. Section 1.9.1. 

‘‘Public Health Significance.’’ p. 1–68. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

288EPA (2013) ISA for Lead. Section 1.9.1. 

‘‘Public Health Significance.’’ p. 1–68. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

289EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. 

EPA/600/R–10/075F, 2013. 

290EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. 

EPA/600/R–10/075F, 2013. 

291EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. 

EPA/600/R–10/075F, 2013. 

292EPA (2013) ISA for Lead. Executive Summary. 

‘‘Effects of Pb Exposure in Adults.’’ p. lxxxviii. 

EPA/600/R–10/075F, 2013. 

293EPA (2013) ISA for Lead. Executive Summary. 

‘‘Public Health Significance.’’ p. xciii. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

294EPA (2013) ISA for Lead. Table ES–1. 

‘‘Summary of causal determinations for the 

relationship between exposure to Pb and health 

effects of exposure to lead.276 277

Examples of other measures of cognitive 

function negatively associated with lead 

exposure include measures of 

intelligence and cognitive development 

and cognitive abilities, such as learning, 

memory, and executive functions, as 

well as academic performance and 

achievement.278

In summarizing the evidence relating 

neurocognitive effects to lead exposure 

metrics, the 2013 Lead ISA notes that 

‘‘in individual studies, postnatal (early 

childhood and concurrent) blood [lead] 

levels are also consistently associated 

with cognitive function decrements in 

children and adolescents.’’ 279 280 The 

2013 Lead ISA additionally notes that 

the findings from experimental animal 

studies indicate that lead exposures 

during multiple early lifestages and 

periods are observed to induce 

impairments in learning, and that these 

findings ‘‘are consistent with the 

understanding that the nervous system 

continues to develop (i.e., 

synaptogenesis and synaptic pruning 

remains active) throughout childhood 

and into adolescence.’’ 281 The 2013 

Lead ISA further notes that ‘‘it is clear 

that [lead] exposure in childhood 

presents a risk; further, there is no 

evidence of a threshold below which 

there are no harmful effects on cognition 

from [lead] exposure,’’ and additionally 

recognizes uncertainty about the 

patterns of [lead] exposure that 

contribute to the blood [lead] levels 

analyzed in epidemiologic studies 

(uncertainties which are greater in 

studies of older children and adults 

than in studies of younger children who 

do not have lengthy exposure 

histories).282 Evidence suggests that 

while some neurocognitive effects of 

lead in children may be transient, some 

lead-related cognitive effects may be 

irreversible and persist into 

adulthood,283 potentially affecting lower 

educational attainment and financial 

well-being.284

The 2013 Lead ISA concluded that 

neurodevelopmental effects in children 

were among the effects best 

substantiated as occurring at the lowest 

blood lead levels, and that these 

categories of effects were clearly of the 

greatest concern with regard to potential 

public health impact.285 For example, in 

considering population risk, the 2013 

Lead ISA notes that ‘‘[s]mall shifts in 

the population mean IQ can be highly 

significant from a public health 

perspective.’’ 286 Specifically, if leadrelated decrements are manifested 

uniformly across the range of IQ scores 

in a population, ‘‘a small shift in the 

population mean IQ may be significant 

from a public health perspective 

because such a shift could yield a larger 

proportion of individuals functioning in 

the low range of the IQ distribution, 

which is associated with increased risk 

of educational, vocational, and social 

failure’’ as well as a decrease in the 

proportion with high IQ scores.287

With regard to lead effects identified 

for the adult population, the 2013 Lead 

ISA concluded that there is a ‘‘causal 

relationship’’ between lead exposure 

and hypertension and coronary heart 

disease in adults. The 2013 Lead ISA 

concluded that cardiovascular effects in 

adults were those of greatest public 

health concern for adults because the 

evidence indicated that these effects 

occurred at the lowest blood lead levels, 

compared to other health effects, 

although it further noted that the role of 

past versus recent exposures to lead is 

unclear.288

With regard to evidence of 

cardiovascular effects and other effects 

of lead on adults, the 2013 Lead ISA 

notes that ‘‘[a] large body of evidence 

from both epidemiologic studies of 

adults and experimental studies in 

animals demonstrates the effect of longterm [lead] exposure on increased blood 

pressure and hypertension.’’ 289 In 

addition to its effect on blood pressure, 

‘‘[lead] exposure can also lead to 

coronary heart disease and death from 

cardiovascular causes and is associated 

with cognitive function decrements, 

symptoms of depression and anxiety, 

and immune effects in adult 

humans.’’ 290 The extent to which the 

effects of lead on the cardiovascular 

system are reversible is not well 

characterized. Additionally, the 

frequency, timing, level, and duration of 

lead exposure causing the effects 

observed in adults has not been 

pinpointed, and higher exposures 

earlier in life may play a role in the 

development of health effects measured 

later in life.291 The 2013 Lead ISA states 

that ‘‘[i]t is clear however, that [lead] 

exposure can result in harm to the 

cardiovascular system that is evident in 

adulthood and may also affect a broad 

array of organ systems.’’ 292 In 

summarizing the public health 

significance of lead on the adult 

population, the 2013 Lead ISA notes 

that ‘‘small [lead]-associated increases 

in the population mean blood pressure 

could result in an increase in the 

proportion of the population with 

hypertension that is significant from a 

public health perspective.’’ 293

In addition to the effects summarized 

here, the EPA has concluded there is a 

‘‘likely to be causal relationship’’ 

between lead exposure and both 

cognitive function decrements and 

psychopathological effects in adults. 

The 2013 Lead ISA also concludes that 

there is a ‘‘causal relationship’’ between 

lead exposure and decreased red blood 

cell survival and function, altered heme 

synthesis, and male reproductive 

function. The EPA has also concluded 

there is a ‘‘likely to be causal 

relationship’’ between lead exposure 

and decreased host resistance, resulting 

in increased susceptibility to bacterial 

infection and suppressed delayed type 

hypersensitivity, and cancer.294


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effects.’’ pp. lxxxiv–lxxxvii. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

295EPA (2013) ISA for Lead. Table ES–1. 

‘‘Summary of causal determinations for the 

relationship between exposure to Pb and health 

effects.’’ pp. lxxxiv–lxxxvi. EPA, Washington, DC, 

EPA/600/R–10/075F, 2013. 

296EPA (2013) ISA for Lead. Chapter 5. 

‘‘Approach to Classifying Potential At-Risk 

Factors.’’ p. 5–2. EPA, Washington, DC, EPA/600/ 

R–10/075F, 2013. 

297EPA (2013) ISA for Lead. Section 5.4. 

‘‘Summary.’’ p. 5–44. EPA, Washington, DC, EPA/ 

600/R–10/075F, 2013. 

298Causal determinations for ecological effects 

were based on integration of information on 

biogeochemistry, bioavailability, biological effects, 

and exposure-response relationships of lead in 

terrestrial, freshwater, and saltwater environments. 

This framework employs a five-level hierarchy that 

classifies the overall weight of evidence with 

respect to the causal nature of relationships 

between criteria pollutant exposures and health and 

welfare effects using the categorizations described 

in the 2013 Lead NAAQS. 

299EPA (2013) ISA for Lead. Table ES–2. 

‘‘Schematic representation of the relationships 

between the various MOAs by which Pb exerts its 

effects.’’ p. lxxxii. EPA, Washington, DC, EPA/600/ 

R–10/075F, 2013. 

300EPA (2013) ISA for Lead. Table ES–2. 

‘‘Summary of causal determinations for the 

relationship between Pb exposure and effects on 

plants, invertebrates, and vertebrates.’’ p. xc. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

301EPA (2013) ISA for Lead. Table ES–2. 

‘‘Summary of causal determinations for the 

relationship between Pb exposure and effects on 

plants, invertebrates, and vertebrates.’’ p. xc. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 

302EPA (2013) ISA for Lead. Table ES–2. 

‘‘Summary of causal determinations for the 

relationship between Pb exposure and effects on 

plants, invertebrates, and vertebrates.’’ p. xc. EPA, 

Washington, DC, EPA/600/R–10/075F, 2013. 303EPA (2013) ISA for Lead. ‘‘Summary.’’ p. xcvi. 

EPA, Washington, DC, EPA/600/R–10/075F, 2013. 

Additionally, in 2013 EPA concluded 

that the evidence is ‘‘suggestive of a 

causal relationship’’ between lead 

exposure and some additional effects. 

These include auditory function 

decrements in adults and subclinical 

atherosclerosis, reduced kidney 

function, birth outcomes (e.g., low birth 

weight, spontaneous abortion), and 

female reproductive function.295

The EPA has identified factors that 

may increase the risk of health effects of 

lead exposure due to susceptibility and/ 

or vulnerability; these are termed ‘‘atrisk’’ factors. The 2013 Lead ISA 

describes the systematic approach the 

EPA uses to evaluate the coherence of 

evidence to determine the biological 

plausibility of associations between atrisk factors and increased vulnerability 

and/or susceptibility. An overall weight 

of evidence is used to determine 

whether a specific factor results in a 

population being at increased risk of 

lead-related health effects.296 The 2013 

Lead ISA concludes that ‘‘there is 

adequate evidence that several factors— 

childhood, race/ethnicity, nutrition, 

residential factors, and proximity to 

[lead] sources—confer increased risk of 

lead-related health effects.’’ 297

3. Welfare Effects and Lead Air 

Pollution 

The 2013 Lead ISA characterizes the 

causal nature of relationships between 

lead exposure and welfare effects using 

a five-level hierarchy that classifies the 

overall weight of evidence.298 We 

summarize here the welfare effects for 

which the EPA has concluded that the 

evidence supports a determination of 

either a ‘‘causal relationship,’’ or a 

‘‘likely to be causal relationship,’’ with 

exposure to lead, or that the evidence is 

‘‘suggestive of a causal relationship’’ 

with lead exposure. The discussion that 

follows is organized to first provide a 

summary of the effects of lead in the 

terrestrial environment, followed by a 

summary of effects of lead in freshwater 

and saltwater ecosystems. The 2013 

Lead ISA further describes the scales or 

levels at which these determinations 

between lead exposure and effects on 

plants, invertebrates, and vertebrates 

were made (i.e., community-level, 

ecosystem-level, population-level, 

organism-level or sub-organism 

level).299

In terrestrial environments, the EPA 

determined that ‘‘causal relationships’’ 

exist between lead exposure and 

reproductive and developmental effects 

in vertebrates and invertebrates, growth 

in plants, survival for invertebrates, 

hematological effects in vertebrates, and 

physiological stress in plants.300 The 

EPA also determined that there were 

‘‘likely to be causal relationships’’ 

between lead exposure and community 

and ecosystem effects, growth in 

invertebrates, survival in vertebrates, 

neurobehavioral effects in invertebrates 

and vertebrates, and physiological stress 

in invertebrates and vertebrates. 

In freshwater environments, the EPA 

found that ‘‘causal relationships’’ exist 

between lead exposure and reproductive 

and developmental effects in vertebrates 

and invertebrates, growth in 

invertebrates, survival for vertebrates 

and invertebrates, and hematological 

effects in vertebrates. The EPA also 

determined that there were ‘‘likely to be 

causal relationships’’ between lead 

exposure and community and 

ecosystem effects, growth in plants, 

neurobehavioral effects in invertebrates 

and vertebrates, hematological effects in 

invertebrates, and physiological stress 

in plants, invertebrates, and 

vertebrates.301

The EPA also determined that the 

evidence for saltwater ecosystems was 

‘‘suggestive of a causal relationship’’ 

between lead exposure and reproductive 

and developmental effects in 

invertebrates, hematological effects in 

vertebrates, and physiological stress in 

invertebrates.302

The 2013 Lead ISA concludes, ‘‘With 

regard to the ecological effects of [lead], 

uptake of [lead] into fauna and 

subsequent effects on reproduction, 

growth and survival are established and 

are further supported by more recent 

evidence. These may lead to effects at 

the population, community, and 

ecosystem level of biological 

organization. In both terrestrial and 

aquatic organisms, gradients in response 

are observed with increasing 

concentration of [lead] and some studies 

report effects within the range of [lead] 

detected in environmental media over 

the past several decades. Specifically, 

effects on reproduction, growth, and 

survival in sensitive freshwater 

invertebrates are well-characterized 

from controlled studies at 

concentrations at or near [lead] 

concentrations occasionally 

encountered in U.S. fresh surface 

waters. Hematological and stress related 

responses in some terrestrial and 

aquatic species were also associated 

with elevated [lead] levels in polluted 

areas. However, in natural 

environments, modifying factors affect 

[lead] bioavailability and toxicity and 

there are considerable uncertainties 

associated with generalizing effects 

observed in controlled studies to effects 

at higher levels of biological 

organization. Furthermore, available 

studies on community and ecosystemlevel effects are usually from 

contaminated areas where [lead] 

concentrations are much higher than 

typically encountered in the 

environment. The contribution of 

atmospheric [lead] to specific sites is 

not clear and the connection between 

air concentration of [lead] and 

ecosystem exposure continues to be 

poorly characterized.’’ 303

B. Final Endangerment Finding 

The Administrator finds, for purposes 

of CAA section 231(a)(2)(A), that lead 

air pollution may reasonably be 

anticipated to endanger the public 

health and welfare. This finding is 

based on consideration of the extensive 

scientific evidence, described in this 

section, that has been amassed over 

decades and rigorously peer reviewed 

by CASAC, as well as consideration of 

public comments on the proposal. 

V. The Final Cause or Contribute 

Finding Under CAA Section 231 

In this action, the Administrator finds 

that engine emissions of lead from 


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304The lead air pollutant can occur as elemental 

lead or in lead-containing compounds, and this 

definition of the air pollutant recognizes the range 

of chemical forms of lead emitted by engines in 

covered aircraft. 

305The lead inventories for 2008, 2011 and 2014 

are provided in the EPA (2018b) Report on the 

Environment Exhibit 2. Anthropogenic lead 

emissions in the U.S. Available at https://

cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead 

inventories for 2017 are available at https://

www.epa.gov/air-emissions-inventories/2017- 

national-emissions-inventory-nei-data#dataq. 

306As described in section II.A.2., the EPA 

estimates 427 tons of lead were emitted by aircraft 

engines operating on leaded fuel in 2020. Due to the 

Covid–19 pandemic, a substantial decrease in 

activity by aircraft occurred in 2020, impacting the 

total lead emissions for this year. The 2020 NEI is 

available at: https://www.epa.gov/air-emissionsinventories/2020-national-emissions-inventory-neidata. 

307Airport lead annual emissions data used were 

reported in the 2017 NEI. Available at https://

www.epa.gov/air-emissions-inventories/2017- 

national-emissions-inventory-nei-data. In addition 

to the triennial NEI, the EPA collects from state, 

local, and Tribal air agencies point source data for 

larger sources every year (see https://www.epa.gov/ 

air-emissions-inventories/air-emissions-reportingrequirements-aerr for specific emissions 

thresholds). While these data are not typically 

published as a new NEI, they are available publicly 

upon request and are also included in https://

www.epa.gov/air-emissions-modeling/emissionsmodeling-platforms, which are created for years 

other than the triennial NEI years. County estimates 

of lead emissions from non-aircraft sources used in 

this action are from the 2019 inventory. There are 

3,012 counties and statistical equivalent areas 

where EPA estimates engine emissions of lead 

occur. 

308FAA. General Aviation and Part 135 Activity 

Surveys—CY 2019. Chapter 3: Primary and Actual 

Use. Table 1.3—General Aviation and Part 135 

Total Hours Flown by Aircraft Type 2008–2019 

(Hours in Thousands). Retrieved on Dec., 27, 2021 

at https://www.faa.gov/data_research/aviation_

data_statistics/general_aviation/CY2019/. 

309 Geidosch. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Past Trends and Future 

Projections in General Aviation Activity and 

Emissions. June 1, 2022. Docket ID EPA–HQ–2022– 

0389. 

310 Geidosch. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Past Trends and Future 

Projections in General Aviation Activity and 

Emissions. June 1, 2022. Docket ID EPA–HQ–2022– 

0389. 

311FAA TAF Fiscal Years 2020–2045 describes 

the forecast method, data sources, and review 

process for the TAF estimates. The documentation 

for the TAF is available at https://taf.faa.gov/ 

Downloads/TAFSummaryFY2020–2045.pdf. 

certain aircraft cause or contribute to the 

lead air pollution that may reasonably 

be anticipated to endanger public health 

and welfare under section 231(a)(2)(A) 

of the Clean Air Act. This section 

describes the definition of the air 

pollutant and the data and information 

supporting the Administrator’s final 

determination. Public comments on the 

cause or contribute finding were largely 

supportive of the EPA’s proposal, 

though some commenters opposed 

finalizing the finding. After 

consideration of the comments on this 

topic, the EPA concludes that the 

scientific evidence supports finalizing 

the finding as proposed. The Agency’s 

responses to certain public comments 

on the cause or contribute finding can 

be found in section V.C. of this 

document, and responses to additional 

comments on the cause or contribute 

finding can be found in the Response to 

Comments document for this action. 

A. Definition of the Air Pollutant 

Under section 231, the Administrator 

is to determine whether emissions of 

any air pollutant from any class or 

classes of aircraft engines cause or 

contribute to air pollution which may 

reasonably be anticipated to endanger 

public health or welfare. As in the 2016 

Findings that the EPA made under 

section 231 for greenhouse gases, in 

making this cause or contribute finding 

under section 231(a)(2), the 

Administrator first defines the air 

pollutant being evaluated. The 

Administrator has reasonably and 

logically considered the relationship 

between the lead air pollution and the 

air pollutant when considering 

emissions of lead from engines used in 

covered aircraft. The Administrator 

defines the air pollutant to match the 

definition of the air pollution, such that 

the air pollutant analyzed for 

contribution mirrors the air pollution 

considered in the endangerment 

finding. Accordingly, for purposes of 

this action, the Administrator defines 

the ‘‘air pollutant’’ referred to in section 

231(a)(2)(A) as lead, which we also refer 

to as the lead air pollutant in this 

document.304 As noted in section II.A.2. 

of this document, lead emitted to the air 

from covered aircraft engines is 

predominantly in particulate form as 

lead dibromide; however, some 

chemical compounds of lead that are 

expected in the exhaust from these 

engines, including alkyl lead 

compounds, would occur in the air in 

gaseous form. 

B. The Data and Information Used To 

Evaluate the Final Cause or Contribute 

Finding 

The Administrator’s assessment of 

whether emissions from the engines 

used in covered aircraft cause or 

contribute to lead air pollution was 

informed by estimates of lead emissions 

from the covered aircraft, lead 

concentrations in air at and near 

airports that are attributable to lead 

emissions from piston engines used in 

covered aircraft, and projected future 

conditions. 

As used in this final action, the term 

‘‘covered aircraft’’ refers to all aircraft 

and ultralight vehicles equipped with 

covered engines which, in this context, 

means any aircraft engine that is capable 

of using leaded avgas. Examples of 

covered aircraft would include smaller 

piston-powered aircraft such as the 

Cessna 172 (single-engine aircraft) and 

the Beechcraft Baron G58 (twin-engine 

aircraft), as well as the largest pistonengine aircraft such as the Curtiss C–46 

and the Douglas DC–6. Other examples 

of covered aircraft would include 

rotorcraft, such as the Robinson R44 

helicopter, light-sport aircraft, and 

ultralight vehicles equipped with piston 

engines. The vast majority of covered 

aircraft are piston-engine powered. 

In recent years, covered aircraft are 

estimated to be the largest single source 

of lead to air in the U.S. Since 2008, as 

described in section II.A.2.b. of this 

document, lead emissions from covered 

aircraft are estimated to have 

contributed over 50 percent of all lead 

emitted to the air nationally. The EPA 

estimates 470 tons of lead were emitted 

by covered aircraft in 2017, comprising 

70 percent of lead emitted to air 

nationally that year.305 306 In 

approximately 1,000 counties in the 

U.S., the EPA’s emissions inventory 

identifies covered aircraft as the sole 

source of lead emissions. Among the 

1,872 counties in the U.S. for which the 

inventory identifies multiple sources of 

lead emissions, including engine 

emissions from covered aircraft, the 

contribution of aircraft engine emissions 

ranges from 0.00005 to 4.3 tons per year, 

comprising 0.15 to 98 percent 

(respectively) of total lead emissions to 

air in those counties.307

Covered aircraft activity, as measured 

by the number of hours flown 

nationwide, increased nine percent in 

the period from 2012 through 2019.308

General aviation activity, largely 

conducted by covered aircraft, increased 

up to 52 percent at airports that are 

among the busiest in the U.S.309 In 

future years, while piston-engine 

aircraft activity overall is projected to 

decrease slightly, this change in activity 

is not projected to occur uniformly 

across airports in the U.S.; some airports 

are forecast to have increased activity by 

general aviation aircraft, the majority of 

which is conducted by piston-engine 

aircraft.310 Although there is some 

uncertainty in these projections, they 

indicate that lead emissions from 

covered aircraft may increase at some 

airports in the future.311

Additionally, engine emissions of 

lead from covered aircraft may deposit 

in the local environment and, due to the 

small size of the lead-bearing particles 

emitted by engines in covered aircraft, 

these particles may disperse widely in 


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312Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment, 45 (32), 5795–5804. 

DOI: https://dx.doi.org/10.1016/ 

j.atmosenv.2011.07.017. 

313EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

Table 6. EPA–420–R–20–003, 2020. Available at 

https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf. 

314Carr et al., 2011. Development and evaluation 

of an air quality modeling approach to assess nearfield impacts of lead emissions from piston-engine 

aircraft operating on leaded aviation gasoline. 

Atmospheric Environment, 45 (32), 5795–5804. 

DOI: https://dx.doi.org/10.1016/ 

j.atmosenv.2011.07.017. 

315Heiken et al., 2014. Quantifying Aircraft Lead 

Emissions at Airports. ACRP Report 133. Available 

at https://www.nap.edu/catalog/22142/quantifyingaircraft-lead-emissions-at-airports. 

316Hudda et al., 2022. Substantial Near-Field Air 

Quality Improvements at a General Aviation Airport 

Following a Runway Shortening. Environmental 

Science & Technology. DOI: 10.1021/ 

acs.est.1c06765. 

317 73 FR 66965 (Nov. 12, 2008). 

318 75 FR 81126 (Dec. 27, 2010). 

319EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports 

Table 6. EPA–420–R–20–003, 2020. Available at 

https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf. 

320EPA’s 2019 AirToxScreen is available at 

https://www.epa.gov/AirToxScreen/2019- 

airtoxscreen. 

321South Coast Air Quality Management District 

(2012) Adoption of 2012 Lead SIP Los Angeles 

County by South Coast Governing Board, p.3–11, 

Table 3–3. Available at https://www.aqmd.gov/ 

home/air-quality/clean-air-plans/lead-stateimplementation-plan. The South Coast Air Quality 

Management District identified 22 airports in the 

Los Angeles County-South Coast Air Basin 

nonattainment area; the Whiteman Airport is among 

those in the nonattainment area and the EPA 

estimated activity at this airport may increase lead 

concentrations to levels above the lead NAAQS in 

the report, Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports. 

Table 7. EPA, Washington, DC, EPA–420–R–20– 

003, 2020. Available at https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf. 

322EPA provides updated information regarding 

nonattainment areas at this website: https://

www.epa.gov/green-book/green-book-lead-2008- 

area-information. 

the environment. Therefore, because 

lead is a persistent pollutant in the 

environment, we anticipate current and 

future emissions of lead from covered 

aircraft engines may contribute to 

exposures and uptake by humans and 

biota into the future. 

In evaluating the contributions of 

engine emissions from covered aircraft 

to the lead air pollution, as defined in 

section IV.A. of this document, the EPA 

also considered three types of 

information about lead concentrations 

in the ambient air: monitored 

concentrations, modeled concentrations, 

and model-extrapolated estimates of 

lead concentrations. Lead 

concentrations monitored in the 

ambient air typically quantify lead 

compounds collected as suspended 

particulate matter. The information 

gained from air monitoring and air 

quality modeling provides insight into 

how lead emissions from piston engines 

used in covered aircraft can affect lead 

concentrations in air. 

As described in section II.A.3. of this 

document, the EPA has conducted air 

quality modeling at two airports and 

extrapolated modeled estimates of lead 

concentrations to 13,000 airports with 

piston-engine aircraft activity. These 

studies indicate that over a three-month 

averaging time (the averaging time for 

the Lead NAAQS), the engine emissions 

of lead from covered aircraft are 

estimated to contribute to air lead 

concentrations to a distance of at least 

500 meters downwind from a 

runway.312 313 Additional studies have 

reported that lead emissions from 

covered aircraft may have increased 

concentrations of lead in air by one to 

two orders of magnitude at locations 

proximate to aircraft emissions 

compared to nearby locations not 

impacted by a source of lead air 

emissions.314 315 316

In 2008 and 2010, the EPA enhanced 

the lead monitoring network by 

requiring monitors to be placed in areas 

with sources such as industrial facilities 

and airports, as described further in 

section II.A.3. of this document.317 318

As part of this 2010 requirement to 

expand lead monitoring nationally, the 

EPA required a 1-year monitoring study 

of 15 additional airports with estimated 

lead emissions between 0.50 and 1.0 ton 

per year in an effort to better understand 

how these emissions affect 

concentrations of lead in the air at and 

near airports. Further, to help evaluate 

airport characteristics that could lead to 

ambient lead concentrations that 

approach or exceed the lead NAAQS, 

airports for this 1-year monitoring study 

were selected based on factors such as 

the level of activity of covered aircraft 

and the predominant use of one runway 

due to wind patterns. Monitored lead 

concentrations in ambient air are highly 

sensitive to monitor location relative to 

the location of the run-up areas for 

piston-engine aircraft and other 

localized areas of elevated lead 

concentrations relative to the air 

monitor locations. 

The lead monitoring study at airports 

began in 2011. In 2012, air monitors 

were placed in close proximity to the 

run-up areas at the San Carlos Airport 

(measurements started on March 10, 

2012) and the McClellan-Palomar 

Airport (measurements started on March 

16, 2012). The concentrations of lead 

measured at both of these airports in 

2012 were above the level of the lead 

NAAQS, with the highest measured 

levels of lead in total suspended 

particles over a rolling three-month 

average of 0.33 micrograms per cubic 

meter of air at the San Carlos Airport 

and 0.17 micrograms per cubic meter of 

air at the McClellan-Palomar Airport. 

These concentrations violate the 

primary and secondary lead NAAQS, 

which are set at a level of 0.15 

micrograms per cubic meter of air 

measured in total suspended particles, 

as an average of three consecutive 

monthly concentrations. 

In recognition of the potential for lead 

concentrations to exceed the lead 

NAAQS in ambient air near the area of 

maximum concentration at airports, the 

EPA further conducted an assessment of 

airports nationwide, titled ‘‘Modelextrapolated Estimates of Airborne Lead 

Concentrations at U.S. Airports’’ and 

described in section II.A.3. of this 

document.319 The model-extrapolated 

lead concentrations estimated in this 

study are attributable solely to 

emissions from engines in covered 

aircraft operating at the airports 

evaluated and did not include other 

sources of lead emissions to air. The 

EPA identified four airports with the 

potential for lead concentrations above 

the lead NAAQS due to lead emissions 

from engines used in covered aircraft. 

Additional information regarding the 

contribution of engine emissions of lead 

from covered aircraft to lead air 

pollution is provided by the EPA’s Air 

Toxics Screening Assessment. As 

described and summarized in section 

II.A.3. of this document, the EPA’s Air 

Toxics Screening Assessment estimates 

that piston engines used in aircraft 

contribute more than 50 percent of the 

estimated lead concentrations in over 

half of the census tracts in the U.S.320

The EPA also notes that lead is 

emitted from engines in covered aircraft 

in three of the ten areas in the U.S. 

currently designated as nonattainment 

for the 2008 lead NAAQS. These areas 

are Arecibo, PR, and Hayden, AZ, each 

of which include one airport servicing 

covered aircraft, and the Los Angeles 

County-South Coast Air Basin, CA, 

which contains at least 22 airports 

within its nonattainment area 

boundary.321 322 Although the lead 

emissions from aircraft are not the 

predominant source of airborne lead in 

these areas, the emissions from covered 

aircraft may increase ambient air lead 

concentrations in these areas. 


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C. Response to Certain Comments on 

the Cause or Contribute Finding 

The EPA received comments related 

to the contribution of lead emissions 

from engines in covered aircraft to lead 

air pollution. Commenters provided 

both support for and opposition to the 

EPA’s proposed cause or contribute 

finding, with specific comments 

regarding the amount of lead emitted by 

aircraft operating on leaded fuel and the 

contribution of aircraft engine emissions 

to lead concentrations in the air. 

Numerous commenters state their 

support for the proposed cause or 

contribute finding, in some cases noting 

that ample evidence supports this 

finding and highlighting the important 

role that lead emissions from covered 

aircraft engines have in local 

environments in many areas of the U.S. 

Additional commenters express concern 

regarding monitored lead concentrations 

that exceed the NAAQS at some 

airports. The comments expressing 

support for the proposed cause or 

contribute finding and EPA’s responses 

are described in greater detail in the 

Response to Comment document for this 

action. We acknowledge these 

comments and the support expressed for 

the EPA’s cause or contribute finding, 

and we agree with the commenters that 

lead emissions from engines in covered 

aircraft contribute to lead air pollution. 

Commenters stating opposition to the 

cause or contribute finding based on the 

amount of lead emitted by aircraft 

operating on leaded fuel, assert that lead 

emissions today are 425 times less than 

lead emissions of the 1970s or that the 

emissions of lead from aircraft are less 

than one quarter of one percent of the 

emissions from cars in the 1970s. Some 

commenters also state that it only stands 

to reason that covered aircraft engine 

emissions of lead represent a high 

percentage of current lead emissions 

because lead is no longer being emitted 

by motor vehicles. At least one 

additional commenter states that given 

the number of hours flown by covered 

aircraft, they do not contribute enough 

lead to affect air pollution. 

Commenters stating opposition to the 

cause or contribute finding based on the 

concentrations of lead in air from engine 

emissions by covered aircraft state that 

concentrations of lead exceeding the 

lead NAAQS are rare, representing two 

of 17 airports studied. One commenter 

also notes that Table 2 (in section II.A.3. 

of this document) does not address the 

localized conditions of the airports 

studied and that the airports where lead 

concentrations violated the lead 

NAAQS may have unique conditions 

that resulted in the concentrations 

measured. Additionally, some 

commenters state that there is no 

evidence that engine emissions of lead 

are creating a hazard, and that the lead 

emitted is not toxic in the small amount 

emitted by aircraft engines. 

In response to commenters comparing 

emissions of lead from covered aircraft 

to lead emitted by motor vehicles in the 

1970s, the EPA acknowledges that more 

lead was emitted by motor vehicles in 

the 1970s than is emitted by covered 

aircraft engines currently. This cause or 

contribute finding is focused on 

emissions of lead from covered aircraft 

engines, a different category of mobile 

sources from motor vehicles, and the 

commenters do not explain why the fact 

that historical emissions were higher 

from a different source category means 

that current emissions from covered 

aircraft engines are not contributing to 

the existing lead air pollution. 

Similarly, the historical contributions of 

lead emitted by motor vehicles is not 

germane to the present-day analysis of 

the contribution of lead emissions from 

covered aircraft engines to the total lead 

released to the air annually in the U.S. 

Indeed, nothing in CAA section 231(a) 

precludes EPA from making a cause or 

contribute finding for emissions from 

aircraft engines where such a finding is 

warranted, even if emissions from other 

sources regulated elsewhere in the CAA 

or under other Federal programs may 

also contribute to that air pollution or 

have historically contributed to it. See 

Massachusetts v. E.P.A., 549 U.S. 497, 

533 (2007) (the alleged efficacy of other 

‘‘Executive Branch programs’’ in 

addressing the air pollution problem is 

not a valid reason for declining to make 

an endangerment finding). As noted 

previously, in making a cause or 

contribute finding, CAA section 231 

does not require the EPA to find that the 

contribution from the relevant source 

category is ‘‘significant,’’ let alone the 

sole or major cause of the endangering 

air pollution. As described in section 

V.B., the lead emissions from engines 

used in covered aircraft clearly 

contribute to the endangering lead air 

pollution, as these emissions 

contributed over 50 percent of lead 

emissions to air starting in 2008, when 

approximately 560 tons of lead were 

emitted by engines in covered aircraft, 

and more recently, in 2017, when 

approximately 470 tons of lead were 

emitted by engines in covered aircraft. 

In the EPA’s view, both the quantity and 

percentage of lead emitted by covered 

aircraft engines amply demonstrate that 

this source contributes to lead air 

pollution in the U.S. 

In response to commenters stating 

that the number of hours flown by 

covered aircraft do not contribute 

enough lead to affect air pollution, the 

EPA notes that the commenters made a 

conclusory allegation and did not 

provide data or analysis supporting 

their claim. The EPA disagrees with this 

comment, and we present data in 

section V.B. of this document 

demonstrating that the activity by 

covered aircraft, which includes the 

number of hours flown, contributes to 

lead air pollution as described in the 

preceding paragraph. 

In response to commenters asserting 

that concentrations of lead exceeding 

the lead NAAQS are rare, representing 

two of 17 airports studied, as an initial 

matter, the EPA notes that nothing in 

section 231(a) of the CAA premises the 

cause or contribute finding on emissions 

from the relevant classes of aircraft 

engines contributing to such 

exceedances in a minimum number of 

air quality regions. More importantly, 

the EPA notes that the purpose of this 

airport monitoring study was not to 

determine the frequency with which 

potential violations of the lead NAAQS 

occur at or near airports, but to 

understand the potential range in lead 

concentrations at a small sample of 

airports and the factors that influence 

those concentrations. As described in 

section II.A.3. of this document, the 

concentrations of lead monitored at and 

near highly active general aviation 

airports is largely determined by the 

placement of the monitor relative to the 

run-up area, and monitor placement 

relative to the run-up area was not 

uniform across the airports studied. The 

EPA fully explains the basis on which 

the Administrator finds that emissions 

of lead from covered aircraft engine 

emissions cause or contribute to lead air 

pollution. The data that support this 

finding are presented in section V.B. 

and, as articulated in section V.D., 

where, among other data, the 

Administrator takes into account the 

fact that in some situations lead 

emissions from covered aircraft have 

contributed and may continue to 

contribute to air concentrations that 

exceed the lead NAAQS. Given that the 

lead NAAQS are established to provide 

requisite protection of public health and 

welfare, the Administrator expresses 

particular concern with contributions to 

concentrations that exceed the lead 

NAAQS, and those contributions are 

part of the support for the conclusion 

that lead emissions from engines in 

covered aircraft cause or contribute to 

the endangering air pollution. 

In response to the comment regarding 

the assertion that the two airports where 

lead concentrations violated the lead 

NAAQS may have unique conditions 


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323The data in Table 2 represent concentrations 

measured at one location at each airport and 

monitors were not consistently placed in close 

proximity to the run-up areas. As described in 

section II.A.3., monitored concentrations of lead in 

air near airports are highly influenced by proximity 

of the monitor to the run-up area. In addition to 

monitor placement, there are individual airport 

factors that can influence lead concentrations (e.g., 

the use of multiple run-up areas at an airport, fleet 

composition, and wind speed). The monitoring data 

reported in Table 2 reflect a range of lead 

concentrations indicative of the location at which 

measurements were made and the specific 

operations at an airport. 

324EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports 

Appendix B, Table B–2. EPA–420–R–20–003, 2020. 

Available at https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf. 

325While the comment does not clearly explain 

what it is referring to with the phrase ‘‘creating a 

hazard,’’ we understand that phrase to align with 

the ‘‘cause’’ portion of the cause or contribute 

findings. 

326The lead inventories for 2008, 2011 and 2014 

are provided in the U.S. EPA (2018b) Report on the 

Environment Exhibit 2. Anthropogenic lead 

emissions in the U.S. Available at https://

cfpub.epa.gov/roe/indicator.cfm?i=13#2. The lead 

inventories for 2017 are available at https://

www.epa.gov/air-emissions-inventories/2017-

national-emissions-inventory-nei-data#dataq. 

327EPA (2020) Model-extrapolated Estimates of 

Airborne Lead Concentrations at U.S. Airports 

Table 7. EPA–420–R–20–003, 2020. Available at 

https://nepis.epa.gov/Exe/ 

ZyPDF.cgi?Dockey=P100YG52.pdf. 

that resulted in the concentrations 

measured, the EPA notes that the 

commenter did not specify or explain 

what localized conditions might lead to 

this result; nor did they provide 

supporting evidence for localized 

conditions occurring in these areas that 

could explain these lead concentrations 

presented in Table 2 of this document. 

The EPA describes in section II.A.3. of 

this document that at both of these 

airports, monitors were located in close 

proximity to the area at the end of the 

runway most frequently used for preflight safety checks (i.e., run-up), and 

monitor placement relative to the runup area is a key factor in evaluating the 

maximum impact location attributable 

to lead emissions from piston-engine 

aircraft. Additionally, as described in 

section II.A.3. of this document, air lead 

concentrations at and downwind from 

airports can be influenced by factors 

such as the use of more than one runup area, wind speed, and the number of 

operations conducted by single- versus 

twin-engine aircraft.323 At the two 

airports at which concentrations of lead 

violated the lead NAAQS, the EPA 

observed a similar fleet composition of 

single- versus twin-engine aircraft 

compared with other airports where onsite measurements were taken; wind 

speeds, which are inversely 

proportional to lead concentration, were 

not lower at the airports with lead 

concentrations violating the lead 

NAAQS compared with other airports; 

and these airports were not unique in 

that the activity by piston-engine 

aircraft was in the range of activity by 

these aircraft at the majority of airports 

where monitors were located.324 The 

EPA thus concludes that these two 

airports do not have unique conditions 

responsible for the concentrations of 

lead that violated the lead NAAQS. 

In response to the comments that 

there is no evidence that engine 

emissions of lead are creating a 

hazard,325 and that the lead emitted is 

not toxic in the small amount emitted 

by aircraft engines, we note that these 

comments conflate the endangerment 

and cause or contribute steps of the 

analysis. The text in section 231(a)(2) 

provides for the EPA to make a finding 

based on a determination that emissions 

of the air pollutant from the covered 

aircraft engine ‘‘causes, or contributes 

to’’ the air pollution. In making a cause 

or contribute finding, the EPA need not 

additionally and separately make a 

determination as to whether the 

emissions from covered aircraft engines 

alone cause endangerment. In section 

IV. of this document, the EPA explained 

why the Administrator is finding that 

the lead air pollution endangers public 

health and welfare. The only remaining 

issue at the second step of the analysis 

is whether emissions from the analyzed 

class or classes of aircraft engines cause 

or contribute to the air pollution that 

may reasonably be anticipated to 

endanger public health and welfare. For 

the reasons described in section V. of 

this document, in the Administrator’s 

judgment, emissions of the lead air 

pollutant from engines in the covered 

aircraft cause or contribute to the lead 

air pollution. 

Additional comments were submitted 

to the EPA regarding the emissions, 

deposition, transport, and fate of lead 

emitted by covered aircraft engines. The 

EPA responds to these comments in the 

Response to Comments Document for 

this action. 

D. Final Cause or Contribute Finding for 

Lead 

Taking into consideration the data 

and information summarized in section 

V. of this document, and the public 

comments received on the proposed 

finding, the Administrator finds that 

engine emissions of the lead air 

pollutant from covered aircraft cause or 

contribute to the lead air pollution that 

may reasonably be anticipated to 

endanger public health and welfare. In 

reaching this conclusion, the 

Administrator noted that piston-engine 

aircraft operate on leaded avgas. That 

operation emits lead-containing 

compounds into the air, contributing to 

lead air pollution in the environment. 

As explained in section II.A. of this 

document, once emitted from covered 

aircraft, lead may be transported and 

distributed to other environmental 

media, where it presents the potential 

for human exposure through air and 

non-air pathways before the lead is 

removed to deeper soils or waterbody 

sediments. In reaching this final finding, 

the Administrator takes into 

consideration different air quality 

scenarios in which emissions of the lead 

air pollutant from engines in covered 

aircraft may cause or contribute to lead 

air pollution. Among these 

considerations, he places weight on the 

fact that current lead emissions from 

covered aircraft are an important source 

of air-related lead in the environment 

and that engine emissions of lead from 

covered aircraft are the largest single 

source of lead to air in the U.S. in recent 

years. In this regard, he notes that these 

emissions contributed over 50 percent 

of lead emissions to air starting in 2008, 

when approximately 560 tons of lead 

was emitted by engines in covered 

aircraft (of the total 950 tons of lead) 

and, more recently, in 2017, when 

approximately 470 tons of lead was 

emitted by engines in covered aircraft 

(of the total 670 tons of lead).326

Additionally, he takes into account 

the fact that in some situations lead 

emissions from covered aircraft have 

contributed and may continue to 

contribute to air concentrations that 

exceed the lead NAAQS. The NAAQS 

are standards that have been set to 

protect public health, including the 

health of sensitive groups, with an 

adequate margin of safety and to protect 

public welfare from any known or 

anticipated adverse effects associated 

with the presence of the pollutant in the 

ambient air. For example, the EPA’s 

monitoring data show that lead 

concentrations at two airports, 

McClellan-Palomar and San Carlos, 

violated the lead NAAQS. The EPA’s 

model-extrapolated estimates of lead 

also indicate that some U.S. airports 

may have air lead concentrations above 

the NAAQS in the area of maximum 

impact from operation of covered 

aircraft.327 Given that the lead NAAQS 

are established to protect public health 

and welfare, contributions to 

concentrations that exceed the lead 

NAAQS are of particular concern to the 

Administrator and are persuasive 

support for the conclusion that lead 

emissions from engines in covered 


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328FAA Terminal Area Forecast provides 

projections of aircraft activity at airports. The 

forecast is available at https://taf.faa.gov and the 

FAA Terminal Area Forecast for Fiscal Years 2020– 

2045 describes the forecast method, data sources, 

and review process for the TAF estimates, available 

at: https://taf.faa.gov/Downloads/ 

TAFSummaryFY2020-2045.pdf. 

329 Geidosch. Memorandum to Docket EPA–HQ– 

OAR–2022–0389. Past Trends and Future 

Projections in General Aviation Activity and 

Emissions. June 1, 2022. Docket ID EPA–HQ–2022– 

0389. 

330See Docket ID Number EPA–HQ–OAR–2006– 

0735. The Tribes that submitted comments were: 

The Bad River Band of Lake Superior Tribe of 

Chippewa Indians, The Quapaw Tribe of Oklahoma, 

The Leech Lake Band of Ojibwe, The Lone Pine 

Paiute-Shoshone Reservation, The Fond du Lac 

Band of Lake Superior Chippewa, and The Mille 

Lacs Band of Ojibwe. 

aircraft cause or contribute to the 

endangering air pollution. 

The Administrator is also concerned 

about the likelihood for these emissions 

to continue to be an important source of 

air-related lead in the environment in 

the future, if uncontrolled. While 

recognizing that national consumption 

of leaded avgas is forecast to decrease 

slightly from 2026 to 2041 

commensurate with overall pistonengine aircraft activity, the 

Administrator also notes that these 

changes are not expected to occur 

uniformly across the U.S.328 For 

example, he takes note of the FAA 

forecasts for airport-specific aircraft 

activity out to 2045 that project 

decreases in activity by general aviation 

at some airports, while projecting 

increases at other airports.329 Although 

there is some uncertainty in these 

projections, they indicate that lead 

emissions from covered aircraft may 

increase at some airports in the future. 

Thus, even assuming that consumption 

of leaded avgas and general aviation 

activity decrease somewhat overall, as 

projected, the Administrator anticipates 

that current concerns about these 

sources of air-related lead will continue 

into the future, without controls. 

Accordingly, the Administrator is 

considering both current levels of 

emissions and anticipated future levels 

of emissions from covered aircraft. In 

doing so, the Administrator finds that 

current levels cause or contribute to 

pollution that may reasonably be 

anticipated to endanger public health 

and welfare. He also is taking into 

consideration the projections that some 

airports may see increases in activity 

while others see decreases, as well as 

the uncertainties in these predictions. 

The Administrator therefore considers 

all this information and data 

collectively to inform his judgment on 

whether lead emissions from covered 

aircraft cause or contribute to 

endangering air pollution. 

Accordingly, for all the reasons 

described, the Administrator concludes 

that emissions of the lead air pollutant 

from engines in covered aircraft cause or 

contribute to the lead air pollution that 

may reasonably be anticipated to 

endanger public health and welfare. 

VI. Statutory Authority and Executive 

Order Reviews 

Additional information about these 

statutes and Executive Orders can be 

found at https://www2.epa.gov/lawsregulations/laws-and-executive-orders. 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 14094: Modernizing Regulatory 

Review 

This action is a ‘‘significant regulatory 

action’’ as defined in Executive Order 

12866, as amended by Executive Order 

14094. Accordingly, EPA submitted this 

action to the Office of Management and 

Budget (OMB) for Executive Order 

12866 review. Documentation of any 

changes made in response to the 

Executive Order 12866 review is 

available in the docket. This action 

finalizes a finding that emissions of the 

lead air pollutant from engines in 

covered aircraft cause or contribute to 

the lead air pollution that may be 

reasonably anticipated to endanger 

public health and welfare. 

B. Paperwork Reduction Act (PRA) 

This action does not impose an 

information collection burden under the 

PRA. The final endangerment and cause 

or contribute findings under CAA 

section 231(a)(2)(A) do not contain any 

information collection activities. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action will not 

impose any requirements on small 

entities. The final endangerment and 

cause or contribute findings under CAA 

section 231(a)(2)(A) do not in-and-ofthemselves impose any new 

requirements on any regulated entities 

but rather set forth the Administrator’s 

finding that emissions of the lead air 

pollutant from engines in covered 

aircraft cause or contribute to lead air 

pollution that may be reasonably 

anticipated to endanger public health 

and welfare. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538 and does 

not significantly or uniquely affect small 

governments. The action imposes no 

enforceable duty on any state, local or 

Tribal governments or the private sector. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have Tribal 

implications as specified in Executive 

Order 13175. The final endangerment 

and cause or contribute findings under 

CAA section 231(a)(2)(A) do not in-andof-themselves impose any new 

requirements but rather set forth the 

Administrator’s final finding that 

emissions of the lead air pollutant from 

engines in covered aircraft cause or 

contribute to lead air pollution that may 

be reasonably anticipated to endanger 

public health and welfare. Thus, 

Executive Order 13175 does not apply 

to this action. 

Tribes have previously submitted 

comments to the EPA noting their 

concerns regarding potential impacts of 

lead emitted by piston-engine aircraft 

operating on leaded avgas at airports on, 

and near, their Reservation Land.330 The 

EPA plans to continue engaging with 

Tribal stakeholders on this issue and 

will offer a government-to-government 

consultation upon request. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

Executive Order 13045 (62 FR 19885, 

April 23, 1997) directs Federal agencies 

to include an evaluation of the health 

and safety effects on children of a 

planned regulation in setting Federal 

health and safety standards. This action 

is not subject to Executive Order 13045 

because it does not propose to establish 

an environmental standard intended to 

mitigate health or safety risks. Although 

the Administrator considered health 

and safety risks as part of the 

endangerment and cause or contribute 

findings under CAA section 

231(a)(2)(A), the findings themselves do 

not impose a standard intended to 

mitigate those risks. However, the EPA’s 

Policy on Children’s Health applies to 

this action. Consistent with this policy, 


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331Sierra Club v. EPA, 47 F.4th 738, 745 (D.C. Cir. 

2022) (‘‘EPA’s decision whether to make and 

publish a finding of nationwide scope or effect is 

committed to the agency’s discretion and thus is 

unreviewable’’); Texas v. EPA, 983 F.3d 826, 834– 

35 (5th Cir. 2020). 

332 81 FR 54422 (Aug. 15, 2016) (2016 Findings); 

74 FR 66496 (2009 Findings). 

333Coalition for Responsible Regulation, Inc. v. 

EPA, 684 F.3d 102 (D.C. Cir. 2012) (subsequent 

history omitted) (affirming 2009 Findings); Biogenic 

CO2 Coalition v. EPA (Doc. No. 1932392, No. 16– 

1358, D.C. Cir., January 26, 2022) (granting 

petitioner’s motion to voluntarily dismiss petition 

for review of 2016 Findings). 

334 In deciding whether to invoke the exception 

by making and publishing a finding that an action 

is based on a determination of nationwide scope or 

effect, the Administrator takes into account a 

number of policy considerations, including his 

judgment balancing the benefit of obtaining the D.C. 

Circuit’s authoritative centralized review versus 

allowing development of the issue in other contexts 

and the best use of agency resources. 

the Administrator considered lead 

exposure risks to children as part of this 

final endangerment finding under CAA 

section 231(a)(2)(A). Information on 

how the Policy was applied is available 

under ‘‘Children’s Environmental 

Health’’ in the SUPPLEMENTARY

INFORMATION section B. of this 

document. A copy of the documents 

pertaining to the impacts on children’s 

health from emissions of lead from 

piston-engine aircraft that the EPA 

references in this action have been 

placed in the public docket for this 

action (Docket EPA–HQ–OAR–2022– 

0389). 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not a ‘‘significant 

energy action’’ because it is not likely to 

have a significant adverse effect on the 

supply, distribution or use of energy. 

Further, we have concluded that this 

action is not likely to have any adverse 

energy effects because the final 

endangerment and cause or contribute 

findings under section 231(a)(2)(A) do 

not in-and-of themselves impose any 

new requirements but rather set forth 

the Administrator’s finding that 

emissions of the lead air pollutant from 

engines in covered aircraft cause or 

contribute to lead air pollution that may 

be reasonably anticipated to endanger 

public health and welfare. 

I. National Technology Transfer and 

Advancement Act (NTTAA) 

This action does not involve technical 

standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations; Executive 

Order 14096: Revitalizing Our Nation’s 

Commitment to Environmental Justice 

for All 

The EPA believes that the human 

health or environmental conditions that 

exist prior to this action result in or 

have the potential to result in 

disproportionate and adverse human 

health or environmental effects on 

communities with environmental justice 

concerns. The EPA conducted an 

analysis of people living within 500 

meters or one kilometer of airports and 

found that there is a greater prevalence 

of people of color and of low-income 

populations within 500 meters or one 

kilometer of some airports compared 

with people living more distant. The 

EPA provides a summary of the 

evidence for potentially 

disproportionate and adverse effects 

among people of color and low-income 

populations residing near airports in 

section II.A.5. of this document. A copy 

of the documents pertaining to the 

EPA’s analysis of potential 

environmental justice concerns 

regarding populations who live in close 

proximity to airports has been placed in 

the public docket for this action (Docket 

EPA–HQ–OAR–2022–0389). 

The EPA believes that this action will 

not change existing disproportionate 

and adverse effects on communities 

with environmental justice concerns. In 

this action, the EPA finds, under section 

231(a)(2)(A) of the Clean Air Act, that 

emissions of lead from engines in 

covered aircraft may cause or contribute 

to air pollution that may reasonably be 

anticipated to endanger public health or 

welfare. We are not proposing emission 

standards at this time. 

The EPA additionally promoted fair 

treatment and meaningful involvement 

for the public, including for 

communities with environmental justice 

concerns, in this action by briefing 

Tribal members on this action and 

providing information on our website in 

both Spanish and English, as well as 

providing access to Spanish translation 

during the public hearing. 

K. Congressional Review Act (CRA) 

The EPA will submit a rule report to 

each House of the Congress and to the 

Comptroller General of the United 

States. This action is not a ‘‘major rule’’ 

as defined by 5 U.S.C. 804(2). 

L. Determination Under Section 307(d) 

Section 307(d)(1)(V) of the CAA 

provides that the provisions of section 

307(d) apply to ‘‘such other actions as 

the administrator may determine.’’ 

Pursuant to section 307(d)(1)(V), the 

Administrator determines that this 

action is subject to the provisions of 

section 307(d). 

M. Judicial Review 

Section 307(b)(1) of the CAA governs 

judicial review of final actions by the 

EPA. This section provides, in part, that 

petitions for review must be filed in the 

D.C. Circuit: (i) when the agency action 

consists of ‘‘nationally applicable 

regulations promulgated, or final actions 

taken, by the Administrator,’’ or (ii) 

when such action is locally or regionally 

applicable, but ‘‘such action is based on 

a determination of nationwide scope or 

effect and if in taking such action the 

Administrator finds and publishes that 

such action is based on such a 

determination.’’ For locally or regionally 

applicable final actions, the CAA 

reserves to the EPA complete discretion 

whether to invoke the exception in (ii) 

described in the preceding sentence.331

This action is ‘‘nationally applicable’’ 

within the meaning of CAA section 

307(b)(1) because in issuing these final 

findings, the EPA becomes subject to a 

statutory duty to propose and 

promulgate aircraft engine emission 

standards under CAA section 231(a), 

which are nationally applicable 

regulations for which judicial review is 

available only in the U.S. Court of 

Appeals for the District of Columbia 

Circuit (D.C. Circuit) pursuant to CAA 

section 307(b)(1). Further, these 

emission standards would apply to 

covered aircraft, wherever in the nation 

they are located. We note also that 

similar actions, including the 2016 

Endangerment and Cause or Contribute 

Findings under CAA section 231 for 

greenhouse gases and the 2009 

Endangerment and Cause or Contribute 

Findings under CAA section 202(a) for 

greenhouse gases, were also nationally 

applicable 332 and were challenged in 

the D.C. Circuit.333

In the alternative, to the extent a court 

finds this final action to be locally or 

regionally applicable, the Administrator 

is exercising the complete discretion 

afforded to him under the CAA to make 

and publish a finding that this action is 

based on a determination of 

‘‘nationwide scope or effect’’ within the 

meaning of CAA section 307(b)(1).334 In 

issuing these final findings, the EPA 

becomes subject to a statutory duty to 

propose and promulgate emissions 

standards under CAA section 231(a), 

which would apply nationwide to 

covered aircraft that travel and operate 

within multiple judicial circuits. As 

described in section III. of this 

document, in making these findings, the 

EPA is applying the same analytical 

framework that the Agency applied in 

the 2016 Endangerment and Cause or 


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Contribute Findings under CAA section 

231 for greenhouse gases and the 2009 

Endangerment and Cause or Contribute 

Findings under CAA section 202(a) for 

greenhouse gases, both of which were 

challenged in the D.C. Circuit, as noted 

above. 

The Administrator finds that this is a 

matter on which national uniformity in 

judicial resolution of any petitions for 

review is desirable, to take advantage of 

the D.C. Circuit’s administrative law 

expertise, and to facilitate the orderly 

development of the law under the Act. 

The Administrator also finds that 

consolidated review of this action in the 

D.C. Circuit will avoid piecemeal 

litigation in the regional circuits, further 

judicial economy, and eliminate the risk 

of inconsistent results, and that a 

nationally consistent approach to the 

CAA’s provisions related to making 

endangerment and cause or contribute 

findings under section 231 of the CAA, 

including for lead air pollution and 

emissions of lead from engines in 

covered aircraft as here, constitutes the 

best use of agency resources. 

For these reasons, this final action is 

nationally applicable or, alternatively, 

the Administrator is exercising the 

complete discretion afforded to him by 

the CAA and finds that this final action 

is based on a determination of 

nationwide scope or effect for purposes 

of CAA section 307(b)(1) and is 

publishing that finding in the Federal 

Register. Under section 307(b)(1) of the 

CAA, petitions for judicial review of 

this action must be filed in the United 

States Court of Appeals for the District 

of Columbia Circuit by December 19, 

2023. 

VII. Statutory Provisions and Legal 

Authority 

Statutory authority for this action 

comes from 42 U.S.C. 7571, 7601 and 

7607. 

List of Subjects 

40 CFR Parts 87 and 1031 

Environmental protection, Air 

pollution control, Aircraft, Aircraft 

engines. 

40 CFR Part 1068 

Environmental protection, 

Administrative practice and procedure, 

Confidential business information, 

Imports, Motor vehicle pollution, 

Penalties, Reporting and recordkeeping 

requirements, Warranties. 

Michael S. Regan, 

Administrator. 

[FR Doc. 2023–23247 Filed 10–19–23; 8:45 am] 

BILLING CODE 6560–50–P 


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