Updated February 24, 2023
Aviation, Air Pollution, and Climate Change
Some Members of Congress have expressed interest in
impact could be from two to four times that of its past CO2
addressing air pollution emissions, greenhouse gas (GHG)
emissions alone.
emissions, and the climate change effects from domestic
and international aviation. Recent legislative proposals
Aside from GHG emissions, aircraft engines emit a number
would provide for sustainable fuel mandates, incentives for
of criteria—or common—pollutants, including nitrogen
airport efficiency improvements, and GHG emission
oxides, carbon monoxide, oxides of sulfur, unburned or
targets, among other requirements.
partially combusted hydrocarbons (also known as volatile
organic compounds [VOCs]), particulates, and other trace
Emissions from Aircraft
compounds. A subset of the VOCs and particulates are
The U.S. Environmental Protection Agency (EPA)
considered hazardous air pollutants.
estimates that transportation—including passenger cars and
light trucks, heavy-duty trucks, buses, trains, ships, and
Emission Reduction Strategies
aircraft—accounted for 37% of carbon dioxide (CO2, the
In an effort to reduce emissions from the aviation sector,
principal GHG) emissions in 2021. While CO2 emissions
the U.S. government, other nations, and international
from passenger cars and light trucks exceed those from
organizations have worked together with the aviation
aircraft in the United States, CO2 emissions from aviation
industry toward improving technologies, increasing the
are currently experiencing a faster rate of growth. All
efficient use of aircraft and airport infrastructure, adopting
aircraft, including military, commercial, and privately
appropriate economic incentives, and setting standards.
chartered, accounted for 11% of the U.S. transportation
sector’s CO
Aircraft Emission Standards: Domestic Process
2 emissions and 4% of all U.S. CO2 emissions in
2021. Commercial aircraft, including those operated by
In the United States, in accordance with Clean Air Act
passenger and all-cargo airlines, accounted for 7% of
(CAA) Section 231 (42 U.S.C. §7571), EPA sets emission
transportation sector and 3% of all emissions. These
levels for specified pollutants, as promulgated in 40 C.F.R.
estimates include emissions from U.S. domestic flights and
Part 87, “Control of Air Pollution from Aircraft and
emissions from international flights departing the United
Aircraft Engines.” EPA sets standards for Federal Aviation
States, referred to as “international bunkering.”
Administration (FAA)-certified aircraft according to the
amount of thrust generated by their engines. Aircraft
In the United States, aggregate CO2 emissions from aircraft
emission standards currently exist for fuel venting, and
have fluctuated due to changes in technology, the economy,
engine hydrocarbons, carbon monoxide, and nitrogen
travel frequency, and military activity, among other
oxides. In 2021, EPA promulgated standards for CO2
reasons. However, since the global financial crisis in 2009,
emissions from aircraft engines. In 2022, EPA finalized
aggregate CO2 emissions from all aircraft types have grown
standards for particulate emissions from certain classes of
steadily, increasing by almost 22% between 2009 and 2019.
engines used by civil subsonic jet aircraft (87 Federal
This increase makes aircraft one of the faster-growing
Register 72312, November 23, 2022), and proposed an
sources of CO2 emissions in the U.S. transportation sector
endangerment finding for lead pollution from gasoline-
over the past decade. This trend was affected, at least
powered, piston-engine aircraft (87 Federal Register 62753,
temporarily, by reduced air travel in 2020 and 2021 due to
October 17, 2022).
Coronavirus Disease 2019 (COVID-19).
The standard-setting language under CAA Section 231 is
The effects of aircraft emissions on the atmosphere are
similar to the statutory language for other mobile sources in
complex, reflecting differing altitudes, geography, time
the CAA (e.g., cars, trucks, buses). However, compared to
horizons, and environmental conditions. Research has
other mobile sources, EPA must meet additional
shown that in addition to CO2 emissions, other factors
requirements in setting emission standards for aircraft and
increase the climate change impacts of aviation. These
aircraft engines: (1) the EPA Administrator must consult
factors include the contribution of aircraft emissions to
with the Administrator of the FAA and the Secretary of the
ozone production; the formation of water condensation
U.S. Department of Transportation (DOT) in developing
trails and cirrus clouds; the emission of various gases and
emission standards; (2) the EPA Administrator cannot
particles, including water vapor, nitrous oxides, sulfates,
change standards if doing so would “significantly increase
and particulates from jet fuel combustion; and the high
noise and adversely affect safety”; and (3) the President
altitude location of the bulk of these emissions. In
may disapprove any such standards if the DOT Secretary
examining the warming and cooling influences of these
finds that they “would create a hazard to aircraft safety.”
factors, the United Nations’ Intergovernmental Panel on
CAA Section 232 requires the FAA to enforce the standards
Climate Change estimated aviation’s total climate change
at the time an engine is certified for emissions under 14
C.F.R. Part 34, “Fuel Venting and Exhaust Emission
https://crsreports.congress.gov

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Aviation, Air Pollution, and Climate Change
Requirements for Turbine Engine Powered Airplanes.”
cover U.S. subsonic jet and propeller-driven aircraft above
Since compliance with the federal standards is determined
certain takeoff weights.
at engine certification, there are no operational emissions
regulations for aircraft.
Upon EPA’s promulgation of the rule, CAA Section 232
requires the FAA to issue regulations to enforce the
Aircraft Emission Standards: International Process
standards and apply such standards when certifying the
Due to the global nature of the aircraft manufacturing
engines of U.S. aircraft manufacturers (87 Federal Register
industry and its customer base, EPA has generally regulated
36076, June 15, 2022). EPA stated that the standards would
emissions from aircraft only after the United States has
make domestically manufactured aircraft engines
negotiated an international agreement through the
competitive in the global marketplace; however, the agency
International Civil Aviation Organization (ICAO). ICAO is
also acknowledged that the rule likely would not spur any
a United Nations specialized agency established in 1944 to
emissions reductions from U.S. aircraft manufacturers
manage the administration and governance of the
beyond their current trends.
Convention on International Civil Aviation (the Chicago
Market-Based Mechanisms
Convention). ICAO has 193 member states, including the
In October 2016, ICAO also agreed on a framework for
United States. ICAO addresses civil aviation (i.e., all
offsetting future carbon emissions from aviation—referred
nonmilitary, private, and commercial aviation).
to as the Market-Based Mechanism, or MBM. ICAO
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 CO
coordinated approach—for example, aircraft noise and
2
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 CO
standards for pollutants from aircraft, unlike EPA’s
2 emissions that cannot
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 CO
oxides essentially ratified what the principal aircraft
2 emissions defined as the average from all
international civil aviation in 2019 and 2020. However, due
manufacturers had already achieved.
to the effects of the Coronavirus Disease 2019 (COVID-19)
Greenhouse Gas Emission Reduction Strategies
pandemic on international air travel in 2020, ICAO adopted
a baseline based solely on 2019 emissions for a three-year
CO2 Emission Standards
pilot phase, and a baseline of 85% of 2019 emissions for the
Since 2010, ICAO has negotiated with the aviation industry
period 2024-2035.
and selected stakeholders to develop international CO2
emission standards for aircraft engines. A delegation of
Participation in CORSIA is voluntary through 2026. The
EPA and FAA representatives have participated in ICAO’s
U.S. aviation industry agreed to participate during ICAO
process. In March 2017, ICAO adopted international CO2
negotiations. To fulfill the U.S. commitments under the
standards for commercial aircraft engines to begin in 2020.
Chicago Convention with respect to the MBM, FAA
The ICAO standards represent the world’s first global
implemented the CORSIA Monitoring, Reporting, and
design certification measure governing CO2 emissions for
Verification Program in 2019 (84 Federal Register 9412,
any industry sector. The standards apply to newly
March 14, 2019). Whether and what additional authorities
developed civil aircraft designs phased-in between January
are required by EPA and FAA to comply with CORSIA’s
1, 2020, and January 1, 2023, and to in-production aircraft
mandatory trading scheme beginning in 2027 is under
after January 1, 2028. They do not apply to already-
consideration.
manufactured aircraft that are currently in use. CO2
Other Reduction Strategies
emissions targets vary by aircraft type and are set as a
Beyond federal and international CO
function of the aircraft’s maximum takeoff weight.
2 emission standards
for aircraft engines, other policy options are available to
reduce GHGs from the aviation sector. These include (1)
In accordance with the ICAO negotiations and the CAA,
taxes or fees on fuel or its carbon content; (2) incentives or
EPA issued a finding that GHG emissions (including CO2
mandates to use sustainable aviation fuels or fuel
emissions) from civil aircraft contribute to the pollution that
alternatives; (3) incentives to modernize air traffic control
causes climate change and endangers U.S. public health and
systems (see CRS In Focus IF11420, Aircraft Noise and Air
welfare (81 Federal Register 54422, August 15, 2016).
EPA’
Traffic Control Modernization); and (4) ground-based
s endangerment finding, under Section 231 of the
measures aimed at reducing GHG emissions from
CAA, laid the necessary foundation for adoption and
nonaircraft operations at airports. EPA and FAA administer
implementation of CO2 standards for U.S. aircraft, in
several initiatives in operations and research, and
consultation with FAA. On January 11, 2021, EPA
collaborate at the national and international levels, in
promulgated GHG emission standards for aircraft engines
support of many of these policies.
equivalent to the CO2 standards adopted by the ICAO (86
Federal Register 2136, January 11, 2021). The standards
Richard K. Lattanzio, Specialist in Environmental Policy
https://crsreports.congress.gov

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Aviation, Air Pollution, and Climate Change

IF11696


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https://crsreports.congress.gov | IF11696 · VERSION 5 · UPDATED

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