# 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 > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2023-23247 ## Record - **Collection:** Federal Register - **Document type:** Rule - **Published:** October 20, 2023 - **Citation:** 88 FR 72372 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Parts 87, 1031, and 1068 [EPA-HQ-OAR-2022-0389; FRL-5934-02-OAR] RIN 2060-AT10 Finding That Lead Emissions From Aircraft Engines That Operate on Leaded Fuel Cause or Contribute to Air Pollution That May Reasonably Be Anticipated To Endanger Public Health and Welfare AGENCY: Environmental Protection Agency (EPA). ACTION: Final action. SUMMARY: In this action, the Administrator finds that lead air pollution may reasonably be anticipated to endanger the public health and welfare within the meaning of the Clean Air Act. The Administrator also finds that engine emissions of lead from certain aircraft cause or contribute to the lead air pollution that may reasonably be anticipated to endanger public health and welfare under the Clean Air Act. DATES: These findings are effective on November 20, 2023. ADDRESSES: The EPA has established a docket for this action under Docket ID No. EPA-HQ-OAR-2022-0389. All documents in the docket are listed in the https://www.regulations.gov website. Publicly available docket materials are available either electronically in https://www.regulations.gov or in hard copy at the EPA Air and Radiation Docket and Information Center, William Jefferson Clinton West Building, Room 3334, 1301 Constitution Ave. NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the Air Docket is (202) 566-1742. FOR FURTHER INFORMATION CONTACT: Ken Davidson, Office of Transportation and Air Quality, Assessment and Standards Division (ASD), Environmental Protection Agency; telephone number: (415) 972-3633; email address: davidson.ken@epa.gov. SUPPLEMENTARY INFORMATION: A. General Information Does this action apply to me? Regulated entities: These final findings do not themselves apply new requirements to entities other than the EPA and the FAA. With respect to requirements for the EPA and the FAA, as indicated in the proposal for this action, if the EPA issues final findings that emissions of lead from certain classes of engines used in certain aircraft cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare, the EPA then becomes subject to a duty to propose and promulgate emission standards pursuant to section 231 of the Clean Air Act. Upon EPA's issuance of regulations, the FAA shall prescribe regulations to ensure compliance with the EPA's emission standards pursuant to section 232 of the Clean Air Act. In contrast to the findings, those future standards would apply to and have an effect on other entities outside the Federal Government. In addition, pursuant to 49 U.S.C. 44714, the FAA has a statutory mandate to prescribe standards for the composition or chemical or physical properties of an aircraft fuel or fuel additive to control or eliminate aircraft emissions which the EPA has found endanger public health or welfare under section 231(a) of the Clean Air Act. In issuing these final findings, the EPA is making such a finding for emissions of lead from engines in covered aircraft. The classes of aircraft engines and of aircraft relevant to this final action are referred to as “covered aircraft engines” and as “covered aircraft,” respectively throughout this document. Covered aircraft engines in this context means any aircraft engine that is capable of using leaded aviation gasoline. Covered aircraft in this context means all aircraft and ultralight vehicles 1 equipped with covered engines. Covered aircraft would, for example, include smaller piston-engine aircraft such as the Cessna 172 (single-engine aircraft) and the Beechcraft Baron G58 (twin-engine aircraft), as well as the largest 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. 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. Entities potentially interested in this final action include those that manufacture and sell covered aircraft engines and covered aircraft in the United States and those who own or operate covered aircraft. Categories that may be affected by a future regulatory action include, but are not limited to, those listed here: Category NAICS a code SIC b code Examples of potentially affected entities Industry 3364412 3724 Manufacturers of new aircraft engines. Industry 336411 3721 Manufacturers of new aircraft. Industry 481219 4522 Aircraft charter services ( i.e., general purpose aircraft used for a variety of specialty air and flying services). Aviation clubs providing a variety of air transportation activities to the general public. Industry 611512 8249 and 8299 Flight training. a North American Industry Classification System (NAICS). 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 3 EPA (2006) A Framework for Assessing Health Risks of Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-05/093F, 2006. 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. 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. 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 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. 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). 13 As noted in section V.A. of this document, the lead air pollutant can occur as elemental lead or in lead-containing compounds. 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. 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. 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 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. 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 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. 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 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. 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. 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. 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 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 12.3.1.1. “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 12.3.1.2. “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 12.3.1.1. “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. 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. 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. 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. 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. 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. 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/. 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 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. 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 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/. 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 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. 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. 67 See FAA's Air Traffic Activity Data. Available at https://aspm.faa.gov/opsnet/sys/airport.asp. 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). 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. 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). 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. 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. 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 2.2.2.1 “Pb Emissions from Piston-engine Aircraft Operating on Leaded Aviation Gasoline and Other Non-road Sources.” pp. 2-7 through 2-10. EPA, Washington, DC, EPA/600/R-10/075F, 2013. 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 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. 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 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 2.2.2.1 “Pb Emissions from Piston-engine Aircraft Operating on Leaded-Aviation Gasoline and Other Non-road Sources.” p. 2-10. EPA, Washington, DC, EPA/600/R-10/075F, 2013. 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. 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. 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. 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 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 total U.S. lead inventory 59% 60% 64% 70% 69% a Due to the Covid-19 Pandemic, a substantial decrease in activity by aircraft occurred in 2020, impacting the total lead emissions for this year. The 2020 NEI is available at: https://www.epa.gov/air-emissions-inventories/2020-national-emissions-inventory-nei-data. At the state level, the EPA estimates of lead emissions from piston-engine aircraft range from 0.3 tons (Rhode Island) to 50.5 tons (California), 47 percent of which is emitted in the landing and takeoff cycle and 53 percent of which the EPA estimates is emitted in-flight, outside the landing and takeoff cycle. 88 Among the counties in the U.S. where the EPA estimates engine emissions of lead from covered aircraft, these lead inventories range from 0.00005 tons per year to 4.3 tons per year and constitute the only source of air-related lead in 1,140 counties (the county estimates of lead emissions include the lead emitted during the landing and takeoff cycle and not lead emitted in-flight). 89 In the counties where engine emissions of lead from aircraft are the sole source of lead to these estimates, annual lead emissions from the landing and takeoff cycle ranged from 0.00015 to 0.74 tons. Among the 1,872 counties in the U.S. with multiple sources of lead, including engine emissions from covered aircraft, the contribution of aircraft engine emissions ranges from 0.00005 to 4.3 tons, comprising 0.15 to 98 percent of the county total, respectively. 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. 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 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. 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 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. 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 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 PM 2.5 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. 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). 110 102 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. 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. 111 73 FR 66965 (Nov. 12, 2008). 112 40 CFR 50.16 (Nov. 12, 2008). 113 75 FR 81126 (Dec. 27, 2010). 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. 114 115 114 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. Airport, State Lead design value, 116 μg/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. 117 117 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. 118 118 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. 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. 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. 123 122 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. 127 124 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. 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. 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. 134 135 132 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. 139 136 EPA (1977) Air Quality Criteria for Lead. Section 6.2.2.1. 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. 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. 141 140 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. 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. 145 142 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. 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 (PM 2.5 ) 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). 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. 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. 153 EPA (2013) ISA for Lead. Section 3.1.3.3. “Dietary Pb Exposure.” p. 3-20 through 3-24. EPA, Washington, DC, EPA/600/R-10/075F, 2013. 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. 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. 162 158 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 7.2.2.2.1.EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986. 162 EPA (1986) Air Quality Criteria for Lead. Section 7.2.2.2.2. EPA, Washington, DC, EPA-600/8-83/028aF-dF (NTIS PB87142386), 1986. 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. 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. 167 166 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. 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. 168 168 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. 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. 170 171 172 169 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. 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. 175 176 177 173 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. 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. 185 178 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. PM 2.5 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. 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. 186 EPA (2020) Model-extrapolated Estimates of Airborne Lead Concentrations at U.S. Airports. EPA, Washington, DC, EPA-420-R-20-003, 2020. 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. 187 188 189 187 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. Because the U.S. has a dense network of airports, many of which have neighboring communities, we quantified the number of people living and children attending school within 500 meters of the approximately 20,000 airports in the U.S. 190 From this analysis, the EPA estimates that approximately 5.2 million people live within 500 meters of an airport runway, 363,000 of whom are children aged five and under. The EPA also estimates that 573 schools attended by 163,000 children in kindergarten through twelfth grade are within 500 meters of an airport runway. 191 190 In this analysis, we included populations living in census blocks that intersected the 500-meter buffer around each runway in the U.S. Potential uncertainties in this approach are described in our report National Analysis of the Populations Residing Near or Attending School Near U.S. Airports. EPA-420-R-20-001, available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf, and in the EPA responses to peer review comments on the report, available here: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YISM.pdf. 191 EPA (2020) National Analysis of the Populations Residing Near or Attending School Near U.S. Airports. EPA-420-R-20-001. Available at https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YG4A.pdf. In order to identify potential disparities in the near-airport population, we also evaluated populations at the state level. Using the U.S. Census population data for each state in the U.S., we compared the percent of people by age, race and indigenous peoples ( i.e., children five and under, Black, Asian, and Native American or Alaska Native) living within 500 meters of an airport runway with the percent by age, race, and indigenous peoples comprising the state population. 192 Using the methodology described in Clarke (2022), the EPA identified states in which children, Black, Asian, and Native American or Alaska Native populations represent a greater fraction of the population living within 500 meters of a runway compared with the percent of these groups in the state population. 193 Results of this analysis are presented in the following tables. 194 This state-level analysis presents summary information for a subset of potentially relevant demographic characteristics. We present data in this section regarding a wider array of demographic characteristics when evaluating populations living near NPIAS airports. 192 Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389. Estimation of Population Size and Demographic Characteristics among People Living Near Airports by State in the United States. May 31, 2022. Docket ID EPA-HQ-2022-0389. 193 Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389. Estimation of Population Size and Demographic Characteristics among People Living Near Airports by State in the United States. May 31, 2022. Docket ID EPA-HQ-2022-0389. 194 These data are presented in tabular form for all states in this memorandum located in the docket: Clarke. Memorandum to Docket EPA-HQ-OAR-2022-0389. Estimation of Population Size and Demographic Characteristics among People Living Near Airports by State in the United States. May 31, 2022. Docket ID EPA-HQ-2022-0389. Among children five and under, there were three states (Nevada, South Carolina, and South Dakota) in which the percent of children five and under living within 500 meters of a runway represents a greater fraction of the population by a difference of one percent or greater compared with the percent of children five and under in the state population (Table 3). Table 3—The Population of Children Five Years and Under Within 500 Meters of an Airport Runway Compared to the State Population of Children Five Years and Under State Percent of children aged five years and under within 500 meters Percent of children aged five years and under within the state Number of children aged five years and under within 500 meters Number of children aged five years and under in the state Nevada 10 8 1000 224,200 South Carolina 9 8 400 361,400 South Dakota 11 9 3,000 71,300 There were nine states in which the Black population represented a greater fraction of the population living in the near-airport environment by a difference of one percent or greater compared with the state as a whole. These states were California, Kansas, Kentucky, Louisiana, Mississippi, Nevada, South Carolina, West Virginia, and Wisconsin (Table 4). Table 4—The Black Population Within 500 Meters of an Airport Runway and the Black Population, by State State Percent black within 500 meters Percent black within the state Black population within 500 meters Black population in the state California 8 7 18,981 2,486,500 Kansas 8 6 1,240 173,300 Kentucky 9 8 3,152 342,800 Louisiana 46 32 14,669 1,463,000 Mississippi 46 37 8,542 1,103,100 Nevada 12 9 1,794 231,200 South Carolina 31 28 10,066 1,302,900 West Virginia 10 3 1,452 63,900 Wisconsin 9 6 4,869 367,000 There were three states with a greater fraction of Asians in the near-airport environment compared with the state as a whole by a difference of one percent or greater: Indiana, Maine, and New Hampshire (Table 5). Table 5—The Asian Population Within 500 Meters of an Airport Runway and the Asian Population, by State State Percent asian within 500 meters Percent asian within the state Asian population within 500 meters Asian population in the state Indiana 4 2 1,681 105,500 Maine 2 1 406 13,800 New Hampshire 4 2 339 29,000 There were five states (Alaska, Arizona, Delaware, South Dakota, and New Mexico) where the near-airport population had greater representation by Native Americans and Alaska Natives compared with the portion of the population they comprise at the state level by a difference of one percent or greater. In Alaska, the disparity in residential proximity to a runway was the largest: 16,020 Alaska Natives were estimated to live within 500 meters of a runway, representing 48 percent of the population within 500 meters of an airport runway. In contrast, Alaska Natives comprise 15 percent of the Alaska state population (Table 6). Table 6—The Native American and Alaska Native Population Within 500 Meters of an Airport Runway and the Native American and Alaska Native Population, by State State Percent Native American and Alaska Native within 500 meters Percent Native American and Alaska Native within the state Native American and Alaska Native populat [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2023-23247. Public record. Not legal advice.