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The Clean Air Act, which
was last amended in 1990, requires EPA to set National Ambient Air Quality
Standards for pollutants considered harmful to public health and the environment.
The Clean Air Act established two types of national air quality standards. Primary
standards set limits to protect public health, including the health
of "sensitive" populations such as asthmatics, children, and the elderly. Secondary
standards set limits to protect public welfare, including protection
against decreased visibility, damage to animals, crops, vegetation, and buildings.
The EPA Office of Air Quality Planning
and Standards (OAQPS) has set National Ambient Air Quality Standards for
six principal pollutants, which are called "criteria" pollutants. They are listed
below. Units of measure for the standards are parts per million (ppm) by volume,
milligrams per cubic meter of air (mg/m3), and micrograms per cubic
meter of air (µg/m3).
EPA AirData
National Ambient Air Quality Standards
| POLLUTANT |
STANDARD
VALUE
* |
STANDARD
TYPE |
Carbon Monoxide (CO) |
| 8-hour Average |
9 ppm |
(10 mg/m3) |
Primary |
| 1-hour Average |
35 ppm |
(40 mg/m3) |
Primary |
Nitrogen Dioxide (NO2) |
| Annual Arithmetic Mean |
0.053 ppm |
(100 µg/m3) |
Primary & Secondary |
Ozone (O3) |
| 1-hour Average |
0.12 ppm |
(235 µg/m3) |
Primary & Secondary |
| 8-hour Average ** |
0.08 ppm |
(157 µg/m3) |
Primary & Secondary |
Lead (Pb) |
| Quarterly Average |
1.5 µg/m3 |
|
Primary & Secondary |
Particulate (PM 10)
Particles with diameters of 10 micrometers or less |
| Annual Arithmetic Mean |
50 µg/m3 |
|
Primary & Secondary |
| 24-hour Average |
150 µg/m3 |
|
Primary & Secondary |
Particulate (PM 2.5)
Particles with diameters of 2.5 micrometers or less
|
| Annual Arithmetic Mean ** |
15 µg/m3 |
|
Primary & Secondary |
| 24-hour Average ** |
65 µg/m3 |
|
Primary & Secondary |
Sulfur Dioxide (SO2) |
| Annual Arithmetic Mean |
0.03 ppm |
(80 µg/m3) |
Primary |
| 24-hour Average |
0.14 ppm |
(365 µg/m3) |
Primary |
| 3-hour Average |
0.50 ppm |
(1300 µg/m3) |
Secondary |
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| * Parenthetical value is an approximately equivalent concentration.
** The ozone 8-hour standard and the PM 2.5 standards are included for
information only. A 1999 federal court ruling blocked implementation
of these standards, which EPA proposed in 1997. EPA has asked the
U.S. Supreme Court to reconsider that decision. The
Updated Air Quality
Standards website has additional information.
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