Aviation, Air Pollution, and Climate Change

Aviation, Air Pollution, and Climate Change

Updated April 26, 2024
Aviation, Air Pollution, and Climate Change
Some Members of Congress have expressed interest in
Aside from GHG emissions, aircraft engines emit a number
addressing air pollution emissions, greenhouse gas (GHG)
of criteria—or common—pollutants, including nitrogen
emissions, and the climate change effects from domestic
oxides, carbon monoxide, oxides of sulfur, unburned or
and international aviation. Recent legislative proposals
partially combusted hydrocarbons (also known as volatile
would provide for sustainable fuel mandates, incentives for
organic compounds [VOCs]), particulates, and other trace
airport efficiency improvements, and GHG emission
compounds. A subset of the VOCs and particulates are
targets, among other requirements.
considered hazardous air pollutants.
Emissions from Aircraft
Emission Reduction Strategies
The U.S. Environmental Protection Agency (EPA)
In an effort to reduce emissions from the aviation sector,
estimates that transportation—including passenger cars and
the U.S. government, other nations, and international
light trucks, heavy-duty trucks, buses, trains, ships, and
organizations have worked together with the aviation
aircraft—accounted for 37% of carbon dioxide (CO2, the
industry toward improving technologies, increasing the
principal GHG) emissions in 2021. While CO2 emissions
efficient use of aircraft and airport infrastructure, adopting
from passenger cars and light trucks exceed those from
appropriate economic incentives, and setting standards.
aircraft in the United States, CO2 emissions from aviation
are currently experiencing a faster rate of growth. All
Aircraft Emission Standards: Domestic Process
aircraft, including military, commercial, and privately
In the United States, in accordance with Clean Air Act
chartered, accounted for 11% of the U.S. transportation
sector’s CO
(CAA) Section 231 (42 U.S.C. §7571), EPA sets emission
2 emissions and 4% of all U.S. CO2 emissions in
levels for specified pollutants, as promulgated in 40 C.F.R.
2021. Commercial aircraft, including those operated by
Part 87, “Control of Air Pollution from Aircraft and
passenger and all-cargo airlines, accounted for 7% of
Aircraft Engines.” EPA sets standards for Federal Aviation
transportation sector and 3% of all emissions. These
Administration (FAA)-certified aircraft according to the
estimates include emissions from U.S. domestic flights and
amount of thrust generated by their engines. Aircraft
emissions from international flights departing the United
States, referred to as “international bunkering.”
emission standards currently exist for fuel venting, and

engine hydrocarbons, carbon monoxide, and nitrogen
In the United States, aggregate CO2 emissions from aircraft
oxides. In 2021, EPA promulgated standards for CO2
have fluctuated due to changes in technology, the economy,
emissions from aircraft engines. In 2022, EPA finalized
travel frequency, and military activity, among other
standards for particulate emissions from certain classes of
reasons. However, since the global financial crisis in 2009,
engines used by civil subsonic jet aircraft (87 FR 72312). In
aggregate CO2 emissions from all aircraft types have grown
2023, EPA finalized an endangerment finding for lead
steadily, increasing by almost 22% between 2009 and 2019.
pollution from gasoline-powered, piston-engine aircraft (88
This increase makes aircraft one of the faster-growing
FR 72372). With this final determination, EPA is required
sources of CO2 emissions in the U.S. transportation sector
to propose and promulgate regulatory standards for lead
over the past decade. This trend was affected, at least
emissions from aircraft engines.
temporarily, by reduced air travel in 2020 and 2021 due to
The standard-setting language under CAA Section 231 is
Coronavirus Disease 2019 (COVID-19).
similar to the statutory language for other mobile sources in
The effects of aircraft emissions on the atmosphere are
the CAA (e.g., cars, trucks, buses). However, compared to
complex, reflecting differing altitudes, geography, time
other mobile sources, EPA must meet additional
horizons, and environmental conditions. Research has
requirements in setting emission standards for aircraft and
shown that in addition to CO2 emissions, other factors
aircraft engines: (1) the EPA Administrator must consult
increase the climate change impacts of aviation. These
with the Administrator of the FAA and the Secretary of the
factors include the contribution of aircraft emissions to
U.S. Department of Transportation (DOT) in developing
ozone production; the formation of water condensation
emission standards; (2) the EPA Administrator cannot
trails and cirrus clouds; the emission of various gases and
change standards if doing so would “significantly increase
particles, including water vapor, nitrous oxides, sulfates,
noise and adversely affect safety”; and (3) the President
and particulates from jet fuel combustion; and the high
may disapprove any such standards if the DOT Secretary
altitude location of the bulk of these emissions. In
finds that they “would create a hazard to aircraft safety.”
examining the warming and cooling influences of these
CAA Section 232 requires the FAA to enforce the standards
factors, the United Nations’ Intergovernmental Panel on
at the time an engine is certified for emissions under 14
Climate Change estimated aviation’s total climate change
C.F.R. Part 34, “Fuel Venting and Exhaust Emission
impact could be from two to four times that of its past CO2
Requirements for Turbine Engine Powered Airplanes.”
emissions alone.
Since compliance with the federal standards is determined
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Aviation, Air Pollution, and Climate Change
at engine certification, there are no operational emissions
Upon EPA’s promulgation of the rule, CAA Section 232
regulations for aircraft.
requires the FAA to issue regulations to enforce the
standards and apply such standards when certifying the
Aircraft Emission Standards: International Process
engines of U.S. aircraft manufacturers (87 FR 36076). EPA
Due to the global nature of the aircraft manufacturing
stated that the standards would make domestically
industry and its customer base, EPA has generally regulated
manufactured aircraft engines competitive in the global
emissions from aircraft only after the United States has
marketplace; however, the agency also acknowledged that
negotiated an international agreement through the
the rule likely would not spur any emissions reductions
International Civil Aviation Organization (ICAO). ICAO is
from U.S. aircraft manufacturers beyond their current
a United Nations specialized agency established in 1944 to
trends.
manage the administration and governance of the
Market-Based Mechanisms
Convention on International Civil Aviation (the Chicago
In October 2016, ICAO also agreed on a framework for
Convention). ICAO has 193 member states, including the
offsetting future carbon emissions from aviation—referred
United States. ICAO addresses civil aviation (i.e., all
to as the Market-Based Mechanism, or MBM. ICAO
nonmilitary, private, and commercial aviation).
member states agreed to implement a “Carbon Offsetting
ICAO’s activities regarding environmental protection focus
and Reduction Scheme for International Aviation
on issues that could benefit most from an industry-wide
(CORSIA) to address any annual increase in total CO2
coordinated approach—for example, aircraft noise and
emissions from international civil aviation (i.e. civil
engine emissions. ICAO has no direct regulatory or
aviation flights that depart in one country and arrive in a
enforcement authority. After member states agree to a
different country) above the 2020 levels, taking into
negotiated set of international standards, they implement
account special circumstances and respective capabilities.”
these standards through their own domestic laws and
CORSIA relies on the use of emissions units from carbon
regulatory processes. Typically, ICAO’s international
markets to offset the amount of CO2 emissions that cannot
standards for pollutants from aircraft, unlike EPA’s
be reduced through the use of sustainable aviation fuels or
regulations for the same pollutants from on-road vehicles,
technological and operational improvements. CORSIA
have consistently avoided technology-forcing requirements.
began in 2021. Compliance was to be measured against a
For example, the most recent ICAO standards for nitrogen
baseline of CO2 emissions defined as the average from all
oxides essentially ratified what the principal aircraft
international civil aviation in 2019 and 2020. However, due
manufacturers had already achieved.
to the effects of the Coronavirus Disease 2019 (COVID-19)
pandemic on international air travel in 2020, ICAO adopted
Greenhouse Gas Emission Reduction Strategies
a baseline based solely on 2019 emissions for a three-year
CO
pilot phase, and a baseline of 85% of 2019 emissions for the
2 Emission Standards
period 2024-2035.
Since 2010, ICAO has negotiated with the aviation industry
and selected stakeholders to develop international CO2
Participation in CORSIA is voluntary through 2026. The
emission standards for aircraft engines. A delegation of
U.S. aviation industry agreed to participate during ICAO
EPA and FAA representatives have participated in ICAO’s
negotiations. To fulfill the U.S. commitments under the
process. In March 2017, ICAO adopted international CO2
Chicago Convention with respect to the MBM, FAA
standards for commercial aircraft engines to begin in 2020.
implemented the CORSIA Monitoring, Reporting, and
The ICAO standards represent the world’s first global
Verification Program in 2019 (84 FR 9412). Whether and
design certification measure governing CO2 emissions for
what additional authorities are required by EPA and FAA to
any industry sector. The standards apply to newly
comply with CORSIA’s mandatory trading scheme
developed civil aircraft designs phased-in between January
beginning in 2027 is under consideration.
1, 2020, and January 1, 2023, and to in-production aircraft
Other Reduction Strategies
after January 1, 2028. They do not apply to already-
Beyond federal and international CO
manufactured aircraft that are currently in use. CO
2 emission standards
2
for aircraft engines, other policy options are available to
emissions targets vary by aircraft type and are set as a
reduce GHGs from the aviation sector. These include (1)
function of the aircraft’s maximum takeoff weight.
taxes or fees on fuel or its carbon content; (2) incentives or
In accordance with the ICAO negotiations and the CAA,
mandates to use sustainable aviation fuels or fuel
EPA issued a finding that GHG emissions (including CO2
alternatives; (3) incentives to modernize air traffic control
emissions) from civil aircraft contribute to the pollution that
systems (see CRS In Focus IF11420, Aircraft Noise and Air
causes climate change and endangers U.S. public health and
Traffic Control Modernization); and (4) ground-based
welfare (81 FR 54422). EPA’s endangerment finding, under
measures aimed at reducing GHG emissions from
Section 231 of the CAA, laid the necessary foundation for
nonaircraft operations at airports. EPA and FAA administer
adoption and implementation of CO2 standards for U.S.
several initiatives in operations and research, and
aircraft, in consultation with FAA. On January 11, 2021,
collaborate at the national and international levels, in
EPA promulgated GHG emission standards for aircraft
support of many of these policies.
engines equivalent to the CO2 standards adopted by the
ICAO (86 FR 2136). The standards cover U.S. subsonic jet
Richard K. Lattanzio, Specialist in Environmental Policy
and propeller-driven aircraft above certain takeoff weights.
IF11696

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Aviation, Air Pollution, and Climate Change

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https://crsreports.congress.gov | IF11696 · VERSION 7 · UPDATED