[Federal Register Volume 88, Number 202 (Friday, October 20, 2023)]
[Rules and Regulations]
[Pages 72372-72404]
[FR Doc No: 2023-23247]

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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.

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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<PHONE_NUMBER>, 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:<PHONE_NUMBER>; email address:
[email protected].

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 piston-engine 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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    \1\ The FAA regulates ultralight vehicles under 14 CFR part 103.
    \2\ Rotorcraft 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.

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    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:

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                                                                                Examples of potentially
              Category                NAICS \a\ code          SIC \b\ code                affected entities
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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.
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\a\ North American Industry Classification System (NAICS).
\b\ Standard 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\
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    \3\ EPA (2006) A Framework for Assessing Health Risks of
Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-
05/093F, 2006.
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    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.
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    \4\ EPA. 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-childrens-health.pdf.
Children's environmental health includes conception, infancy, early
childhood and through adolescence until 21 years of age.
    \5\ EPA (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.
    \6\ EPA (2013) ISA for Lead. Executive Summary ``Effects of Pb
Exposure in Children.'' pp. lxxxvii-lxxxviii. EPA/600/R-10/075F,
2013.
    \7\ EPA (2013) ISA for Lead. Section 1.9.4. ``Pb Exposure and
Neurodevelopmental Deficits in Children.'' p. I-75. EPA/600/R-10/
075F, 2013.
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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
Piston-Engine 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

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 (twin-engine
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
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    \8\ As noted in section IV.A. of this document, the lead air
pollution can occur as elemental lead or in lead-containing
compounds.
    \9\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \10\ EPA (2006) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA/600/R-5/144aF, 2006.
    \11\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-83/028aF-dF, 1986.
    \12\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
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    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).
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    \13\ As noted in section V.A. of this document, the lead air
pollutant can occur as elemental lead or in lead-containing
compounds.
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    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.
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    \14\ EPA (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).
    \15\ Of 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.
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    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\
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    \16\ U.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.
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    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

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
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    \17\ Under section 108(a)(2) of the CAA, air quality criteria
are intended to ``accurately reflect the latest 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).
    \18\ Section 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.''
    \19\ EPA (2013) ISA for Lead. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \20\ The 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.
    \21\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
    \22\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \23\ EPA (2006) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA/600/R-5/144aF, 2006.
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    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\
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    \24\ EPA (2013) ISA for Lead. Section 3.1.1. ``Pathways for Pb
Exposure.'' p. 3-1. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \25\ EPA (2013) ISA for Lead. Section 3.7.1. ``Exposure.'' p. 3-
144. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \26\ EPA (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.
    \27\ EPA (2013) ISA for Lead. Section 2.3. ``Fate and Transport
of Pb.'' p. 2-24. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \28\ EPA (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.
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    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.
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    \29\ EPA (2013) ISA for Lead. Section 3.1.1.''Pathways for Pb
Exposure.'' p. 3-1. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \30\ EPA (2013) ISA for Lead. Sections 1.3. ``Exposure to
Ambient Pb.'' p. 1-11. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
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    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 piston-engine air traffic,
but not in adults living near multi-runway airports, suggesting the
potential for adverse adult health effects near some airports.\40\
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    \31\ EPA (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.
    \32\ EPA (2006) Air Quality Criteria for Lead. Chapter 3. EPA,
Washington, DC, EPA/600/R-5/144aF, 2006.
    \33\ EPA (1986) Air Quality Criteria for Lead. Section 1.11.3.
EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \34\ EPA (1977) Air Quality Criteria for Lead. Section <IP_ADDRESS>.
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017
(NTIS PB280411), 1977.
    \35\ EPA (1977) Air Quality Criteria for Lead. Section <IP_ADDRESS>.
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017
(NTIS PB280411), 1977.
    \36\ EPA (1977) Air Quality Criteria for Lead. Section <IP_ADDRESS>.
``Air Exposures.'' p. 12-10. EPA, Washington, DC, EPA-600/8-77-017
(NTIS PB280411), 1977.
    \37\ Miranda et al., 2011. A Geospatial Analysis of the Effects
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental
Health Perspectives. 119:1513-1516.
    \38\ Zahran 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.
    \39\ Zahran 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 Piston-Engine Air Traffic in North
Carolina. International Journal of Environmental Research and Public
Health. 19(10):5941.
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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 (single-engine 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

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 piston-engine aircraft until the
early 1970s when 100LL became the dominant leaded fuel in use.
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    \41\ ASTM International (May 1, 2021) Standard Specification for
Leaded Aviation Gasolines D910-21.
    \42\ National 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.
    \43\ Ogston 1981. A Short History of Aviation Gasoline
Development, 1903-1980. Society of Automotive Engineers. p. 810848.
    \44\ U.S. Department of Commerce Civil Aeronautics
Administration. Statistical Handbook of Aviation (Years 1930-1959).
https://babel.hathitrust.org/cgi/pt?id=mdp.39015027813032&view=1up&seq=899.
    \45\ U.S. Department of Commerce Civil Aeronautics
Administration. Statistical Handbook of Aviation (Years 1960-1971).
https://babel.hathitrust.org/cgi/pt?id=mdp.39015004520279&view=1up&seq=9&skin=2021.
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    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.
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    \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.
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    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.
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    \49\ See FAA. NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
    \50\ FAA (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.
    \51\ See FAA's NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
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    As of 2019, there were 171,934 piston-engine 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
single-engine 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
piston-engine 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

student pilots and 466,900 non-student pilots. In addition, there were
more than 301,000 FAA Non-Pilot Certificated mechanics.\60\
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    \52\ FAA. 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/.
    \53\ FAA. 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/wp-content/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/wp-content/uploads/GAMA_2019Databook_Final-2020-03-20.pdf.
    \56\ There are both fixed-wing and rotary-wing aircraft; and
airplane is an engine-driven, fixed-wing aircraft and a rotorcraft
is an engine-driven rotary-wing aircraft.
    \57\ See 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.
    \58\ FAA 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.
    \59\ FAA. 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.
    \60\ FAA. 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.
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    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\
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    \61\ FAA. 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/.
    \62\ FAA. 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/.
    \63\ FAA. 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/.
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    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 piston-engine 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\
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    \64\ FAA. 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/.
    \65\ FAA. 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.
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    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.
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    \67\ See FAA's Air Traffic Activity Data. Available at https://aspm.faa.gov/opsnet/sys/airport.asp.
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    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).
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    \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.
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    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).
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    \69\ FAA'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.
    \70\ The 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.

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2. Emissions of Lead From Piston-Engine Aircraft
    This section describes the physical and chemical characteristics of
lead emitted by covered aircraft and the national, state, county and
airport-specific 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.
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    \71\ EPA (1977) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-77-017 (NTIS PB280411), 1977.
    \72\ EPA (1986) Air Quality Criteria for Lead. EPA, Washington,
DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \73\ EPA (2013) ISA for Lead. Section <IP_ADDRESS> ``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.
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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\
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    \74\ EPA (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.
    \76\ EPA (1986) Air Quality Criteria for Lead. Volume 2:
Chapters 5 & 6. EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS
PB87142386), 1986.
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    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\
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    \77\ EPA (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.
    \78\ EPA (2013) ISA for Lead. Section <IP_ADDRESS> ``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.
    \79\ One 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.
    \80\ Memorandum 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.
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    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 piston-engine 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 5.7x10\6\ to 8.6x10\6\ particles per cm\3\. 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.
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    \81\ Swiss 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/pollutant-
emissions/aircraft-engine-emissions/report_appendices_database-
and-data-sheets.html. Retrieved on June 15, 2022.
    \82\ Swiss 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/pollutant-emissions/aircraft-engine-
emissions/report_appendices_database-and-data-sheets.html.
Retrieved on June 15, 2022.
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b. Inventory of Lead Emitted by Piston-Engine 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

Aviation Gasoline \85\ and in the document titled ``Calculating Piston-
Engine 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 in-flight, 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\
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    \83\ The 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.
    \84\ EPA 2017 NEI. Available at https://www.epa.gov/air-emissions-inventories/2017-national-emissions-inventory-nei-data.
    \85\ Advance Notice of Proposed Rulemaking on Lead Emissions
from Piston-Engine Aircraft Using Leaded Aviation Gasoline. 75 FR
2440 (April 28, 2010).
    \86\ Airport 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).
    \87\ The 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.

                                 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              59%          60%          64%          70%          69%
 total U.S. lead inventory.....................
----------------------------------------------------------------------------------------------------------------
\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.
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    \88\ Lead 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.
    \89\ Airport 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-reporting-requirements-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/emissions-modeling-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.
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    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
airport-specific 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\
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    \90\ See EPA lead inventory data available at https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms.
    \91\ EPA 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.
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    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\
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    \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.
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3. Concentrations of Lead in Air Attributable to Emissions From Piston-
Engine 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

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
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    \93\ Carr et al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field 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.
    \94\ Feinberg 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.
    \95\ Municipality 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%20Study_2012/Merrill%20Field%20Lead%20Study%20Report%20-%20final.pdf.
    \96\ Environment Canada (2000) Airborne Particulate Matter, Lead
and Manganese at Buttonville Airport. Toronto, Ontario, Canada:
Conor Pacific Environmental Technologies for Environmental
Protection Service, Ontario Region.
    \97\ Fine 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/air-quality-monitoring-studies/general-aviation-study/study-of-air-toxins-near-van-nuys-and-santa-monica-airport.pdf.
    \98\ Lead emitted from piston-engine aircraft in the particulate
phase would also be measured in samples collected to evaluate total
ambient PM2.5 concentrations.
    \99\ One 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.
    \100\ EPA (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).
    \101\ EPA (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.
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    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
run-up 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\
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    \102\ Carr et al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field 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.
    \103\ Heiken et al., 2014. Quantifying Aircraft Lead Emissions
at Airports. ACRP Report 133. Available at https://www.nap.edu/catalog/22142/quantifying-aircraft-lead-emissions-at-airports.
    \104\ Hudda 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.
    \105\ Fine 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/air-quality-monitoring-studies/general-aviation-study/study-of-air-toxins-near-van-nuys-and-santa-monica-airport.pdf.
    \106\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \107\ EPA (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.
    \108\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \109\ Feinberg 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.
    \110\ Feinberg 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.
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    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.
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    \111\ 73 FR 66965 (Nov. 12, 2008).
    \112\ 40 CFR 50.16 (Nov. 12, 2008).
    \113\ 75 FR 81126 (Dec. 27, 2010).
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    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

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
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    \114\ EPA (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.
    \115\ EPA (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.
    \116\ A 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.

    Table 2--Lead Concentrations Monitored at 17 Airports in the U.S.
------------------------------------------------------------------------
                                                 Lead design value,\116\
                 Airport, State                         [mu]g/m\3\
------------------------------------------------------------------------
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\
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    \117\ As 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.
---------------------------------------------------------------------------

    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 run-up 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\
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    \118\ The 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.
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    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 model-extrapolated 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

from the location of highest concentration.
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    \119\ EPA (2020) Model-Extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \120\ EPA (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.
---------------------------------------------------------------------------

    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\
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    \122\ Prior 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).
    \123\ EPA (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.
---------------------------------------------------------------------------

    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\ Model-
extrapolated 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 piston-engine 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\
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    \124\ EPA (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.
    \125\ See methods used in EPA (2020) Model-extrapolated
Estimates of Airborne Lead Concentrations at U.S. Airports. Table 2.
p.23. EPA, Washington, DC, EPA-420-R-20-003, 2020.
    \126\ EPA (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.
    \127\ Carr et al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field impacts of lead
emissions from piston-engine aircraft operating on leaded aviation
gasoline. Atmospheric Environment 45: 5795-5804.
---------------------------------------------------------------------------

    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 ``Model-extrapolated
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. Airport-
specific assessments would be needed to determine the magnitude of the
potential range in lead concentrations at and downwind of each
facility.
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    \128\ EPA (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.
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    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 area-weighted census block
concentrations within the tract. Lead concentrations reported in the
AirToxScreen are based on emissions estimates from

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.
---------------------------------------------------------------------------

    \129\ See EPA's 2019 AirToxScreen. Available at https://www.epa.gov/AirToxScreen/2019-airtoxscreen.
    \130\ These 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.
    \131\ As 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.
---------------------------------------------------------------------------

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 start-up, 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
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    \132\ Swiss 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/pollutant-
emissions/aircraft-engine-emissions/report-appendices_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.
    \134\ EPA (2013) ISA for Lead. Section 1.3. ``Exposure to
Ambient Pb.'' p. 1-11. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \135\ The EPA received comments on the information provided in
this section to which we respond in the Response to Comments
document for this action.
---------------------------------------------------------------------------

    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\
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    \136\ EPA (1977) Air Quality Criteria for Lead. Section <IP_ADDRESS>.
EPA, Washington, DC, EPA-600/8-77-017, 1977.
    \137\ EPA (2006) Air Quality Criteria for Lead. Section E.6.
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \138\ EPA (2006) Air Quality Criteria for Lead. Section E.6. p.
2-5. EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \139\ EPA (2006) Air Quality Criteria for Lead. Section 2. EPA,
Washington, DC, EPA/600/R-5/144aF, 2006.
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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\
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    \140\ EPA (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.
    \141\ Memorandum to Docket EPA-HQ-OAR-2022-0389. Deposition of
Lead Emitted by Piston-engine Aircraft. June 15, 2022. Docket ID
EPA-HQ-2022-0389.
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    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\
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    \142\ EPA (2013) ISA for Lead. Section 2.6.1. ``Soils.'' p. 2-
118. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \143\ EPA (2013) ISA for Lead. Chapter 6. ``Ecological Effects
of Pb.'' p. 6-57. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \144\ Murphy et al., 2008. Weekly patterns of aerosol in the
United States. Atmospheric Chemistry and Physics. 8:2729-2739.
    \145\ Lead concentrations collected as part of the Interagency
Monitoring of Protected Visual Environments (IMPROVE) network and
the National Oceanic and Atmospheric Administration (NOAA)
monitoring sites.
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    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

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 aircraft-induced 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).
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    \146\ Heiken 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.
    \147\ McCumber 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.
    \149\ Heiken 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.
    \150\ EPA (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.
    \151\ Environment Canada (2000) Airborne Particulate Matter,
Lead and Manganese at Buttonville Airport. Toronto, Ontario, Canada:
Conor Pacific Environmental Technologies for Environmental
Protection Service, Ontario Region.
    \152\ Lejano 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.
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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, piston-engine 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.
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    \153\ EPA (2013) ISA for Lead. Section <IP_ADDRESS>. ``Dietary Pb
Exposure.'' p. 3-20 through 3-24. EPA, Washington, DC, EPA/600/R-10/
075F, 2013.
    \154\ EPA (2006) Air Quality Criteria for Lead. Section 8.2.2.
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \155\ EPA (2006) Air Quality Criteria for Lead. Section 8.2.2.
EPA, Washington, DC, EPA/600/R-5/144aF, 2006.
    \156\ O'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-applicator-cert-core-manual-2014.pdf.
    \157\ The 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.
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    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\
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    \158\ EPA (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.
    \159\ EPA (2006) Air Quality Criteria for Lead. p. AXZ7-39. EPA,
Washington, DC, EPA/600/R-5/144aF, 2006.
    \160\ EPA (1986) Air Quality Criteria for Lead. Sections 6.5.3.
EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986.
    \161\ EPA (1986) Air Quality Criteria for Lead. Section
<IP_ADDRESS>.1.EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS
PB87142386), 1986.
    \162\ EPA (1986) Air Quality Criteria for Lead. Section
<IP_ADDRESS>.2. EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS
PB87142386), 1986.
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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.
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    \163\ EPA (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.
    \164\ EPA (2002) Persistent, Bioaccumulative, and Toxic
Pollutants (PBT) Program. PBT National Action Plan for Alkyl-Pb.
Washington, DC. June. 2002.
    \165\ See FAA's NASR. Available at https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/eNASR_Browser/.
---------------------------------------------------------------------------

    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

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\
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    \166\ National 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.
    \167\ Memorandum 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.
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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 near-airport population, with attention to
implications related to environmental justice (EJ) and the population
of children in this near-source environment.\168\
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    \168\ As 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.
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    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
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    \169\ See, https://www.federalregister.gov/documents/2023/04/26/2023-08955/revitalizing-our-nations-commitment-to-environmental-justice-for-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-guide-final.pdf. See also https://www.epa.gov/environmentaljustice.
    \170\ EPA (2013) ISA for Lead. Section 5.4. ``Summary.'' p. 5-
40. EPA, Washington, DC, EPA/600/R-10/075F, 2013.
    \171\ EPA. 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.
    \172\ The 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.
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    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
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    \173\ This analysis used the U.S. Census and demographic data
from 2010 which was the most recent data available at the time of
this assessment.
    \174\ Residential 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.
    \175\ Miranda et al., 2011. A Geospatial Analysis of the Effects
of Aviation Gasoline on Childhood Blood Lead Levels. Environmental
Health Perspectives. 119:1513-1516.
    \176\ Zahran 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.
    \177\ Zahran et al., 2022. Leaded Aviation Gasoline Exposure
Risk and Child Blood Lead Levels. Proceedings of the National
Academy of Sciences Nexus. 2:1-11.
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    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

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\
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    \178\ Rowangould 2013. A census of the near-roadway 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.
    \179\ Marshall 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.
    \180\ Marshall 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.
    \181\ Tessum et al., 2021. PM2.5 polluters
disproportionately and systemically affect people of color in the
United States. Science Advances 7:eabf4491.
    \182\ Mohai et al., 2009. Environmental justice. Annual Reviews
34:405-430. Available at https://doi.org/10.1146/annurev-environ-082508-094348.
    \183\ McNair 2020. Investigation of environmental justice
analysis in airport planning practice from 2000 to 2010.
Transportation Research Part D 81:102286.
    \184\ Woodburn 2017. Investigating neighborhood change in
airport-adjacent communities in multiairport regions from 1970 to
2010. Journal of the Transportation Research Board, 2626, 1-8.
    \185\ Rissman et al., 2013. Equity and health impacts of
aircraft emissions at the Hartfield-Jackson Atlanta International
Airport. Landscape and Urban Planning, 120: 234-247.
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    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.
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    \186\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
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    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
piston-engine 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 piston-engine 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
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    \187\ EPA (2020) Model-extrapolated Estimates of Airborne Lead
Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-
003, 2020.
    \188\ Carr et al., 2011. Development and evaluation of an air
quality modeling approach to assess near-field 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.
    \189\ We 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 piston-engine
aircraft at airports nationwide suggests that exposure to lead from
aircraft emissions is likely to vary widely.