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Particulate Matter in Air - Benchmarks, Standards and Guidelines Established
to Protect Public Health
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Note: EPA no longer updates this information, but it may be useful as a reference or resource. |
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Fine Particulate Matter (PM 2.5) in Air
Airborne particles like smoke and dust are solids and liquid droplets
of different sizes suspended in the air. EPA sets the screening level
to caution sensitive groups, including people with heart or lung disease,
older adults, and children. For fine particles, that level is 40 ug/m3*
(the mass of fine particles in micrograms (a millionth of a gram) in a
cubic meter of air) for 24-hour average exposure. This level is based
on EPA's Air Quality Index. Above this level, we recommend that sensitive
groups reduce their exposure. Shorter term peaks are also of potential
concern for sensitive groups. The screening level for the general population
is 65 ug/m3 over a 24-hour period. Most healthy adults and children are
expected to recover quickly from any symptoms of short-term exposure like
coughing, wheezing, or eye and throat irritation.
Coarse Particulate Matter (PM 10) in Air
Particles in the air can be different sizes; when smaller than 10 micrometers
in diameter, they can be inhaled into the lungs. These particles, also
called "PM10," include both fine smoke and coarse dust ("coarse"
dust particles are between 2.5 and 10 micrometers in diameter). EPA sets
the screening level for PM10 to caution sensitive groups, people with
heart or lung disease, older adults, and children, about exposures to
coarse dust particles. The PM10 screening level for sensitive groups is
150 ug/m3* (the mass of coarse particles in micrograms - a millionth of
a gram - in a cubic meter of air) for 24-hour average exposure. This level
is based on EPA's Air Quality Index. Above this level, we recommend that
sensitive groups reduce their exposure. The screening level for the general
population is 250 ug/m3 over a 24-hour period. Most healthy adults, children
and the elderly are expected to recover quickly from any symptoms of short-term
exposure like coughing, wheezing, or eye or throat irritation.
* The unit, ug/m3, is the mass of fine particles in micrograms (a millionth
of a gram) in a cubic meter of air.
See the Particulate Matter Fact Sheet
for more information about particulate matter and how to reduce your exposure.
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