The National Ambient Air Quality Standards for Particle Pollution

SUMMARY OF PROPOSAL TO RETAIN THE AIR QUALITY STANDARDS FOR PARTICLE
POLLUTION

On April 14, 2020 U.S. Environmental Protection Agency (EPA) proposed to retain the nation's air quality

standards for particle pollution, also referred to as particulate matter or PM.

THE PROPOSED STANDARDS

•	The Clean Air Act requires EPA to set two types of outdoor air quality standards: primary standards, to
protect public health, and secondary standards, to protect the public against adverse environmental
effects. The law requires that primary standards be "requisite to protect public health with an adequate
margin of safety," including the health of sensitive groups of people. For PM, the evidence suggests that
people with heart or lung disease, children and older adults, and nonwhite populations are at particular
risk. Secondary standards must be "requisite to protect the public welfare" from both known and
anticipated adverse effects.

•	EPA will accept public comment for 60 days after the proposed standards are published in the Federal
Register. Details on virtual public hearings will be announced shortly. EPA will issue the final standards by
the end of 2020.

Primary (Health) Standards for Fine Particles:

•	EPA sets both an annual and a 24-hour standard for fine particles (PM2.5). These standards work
together to protect the public from harmful health effects from both long- and short-term fine particle
exposures.

•	EPA reviewed thousands of studies as part of this review of the standards, including hundreds of new
studies published since EPA completed the last review in 2012. The new evidence includes many new
epidemiological, controlled human exposure, and animal toxicological studies. EPA also considered
analyses by agency experts and input from the Clean Air Scientific Advisory Committee (CASAC).

•	Annual standard: The annual fine particle standard is designed to protect against health effects
associated with both long- and short- term exposure to PM2.5. The current annual standard has been in
place since 2012.

o EPA is proposing to retain the current annual standard, with its level of 12.0 |ig/m3. An area
would meet the standard if the three-year average of its annual average PM2.5 concentration is
less than or equal to the level of the standard.

•	24-hour standard: The 24-hour primary standard is designed to provide supplemental health
protection against short-term fine particle exposures, particularly in areas with high peak PM2.5
concentrations. The current 24-hour standard was issued in 2006.

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o EPA is proposing to retain the existing 24-hour standard, with its level of 35 |ig/m3. An area
would meet the 24-hour standard if the 98th percentile of the yearly distribution of 24-hour
PM2.5 concentrations, averaged over three years, is less than or equal to 35 |-ig/m3.

Primary (Health) Standard for Coarse Particles

•	EPA is proposing to retain the existing 24-hour primary standard for coarse particles (PM10), with its
level of 150 |-ig/m3. An area meets the 24-hour PM10 standard if it does not exceed the 150 |-ig/m3 level
more than once per year on average over a three-year period.

•	The existing coarse particle standard has been in place since 1987.

Secondary Standards for Particle Pollution:

•	Particle pollution causes haze in cities and some of the country's most treasured national parks. In
addition, particles such as nitrates and sulfates contribute to acid rain formation which erodes buildings,
historical monuments, and paint on cars. Particle pollution also can affect the climate by absorbing or
reflecting sunlight, contributing to cloud formation and influencing rainfall patterns.

•	EPA's current secondary standards for particle pollution are identical to the primary standards for PM2.5
and PM10, except for the annual PM2.5 standard which has a level of 15.0 |-ig/m3. After reviewing the
science on particle pollution, analysis by EPA experts and advice from the agency's independent science
advisors, the Clean Air Scientific Advisory Committee (CASAC), EPA is proposing that the current secondary
standards are adequate to protect against PM-related visibility impairment, climate effects, and effects on
materials.

BACKGROUND

•	EPA has regulated particle pollution since 1971. The agency has revised the standards four times - in 1987,
1997, 2006 and 2012 - to ensure they continue to protect public health and welfare. A table of historical
PM standards is available at http://www.epa.gOv/ttn/naaqs/standards/pm/s pm history.html)

•	The Clean Air Act requires EPA to review national air quality standards every five years to determine
whether they should be retained or revised.

FOR MORE INFORMATION:

•	To read the proposal, visit https://www.epa.gov/naaqs/particulate-matter-pm-standards-federal-register-notices-
current-review

For technical documents related to this review of the standards, visit https://www.epa.gov/naaqs/particulate-

matter-pm-air-qualitv-standards

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