The Clean Air Act requires the EPA to establish National Ambient Air Quality Standards (NAAQS) for six pollutants considered harmful to public health and the environment: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. The standards were set at the level required to provide an ample margin of safety to protect the public health. The six pollutants were chosen based on two criteria:
(1) Emissions cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare; and
(2) Presence in the ambient air results from numerous or diverse mobile or stationary sources.
The Clean Air Act established two types of national air quality standards. Primary standards are intended 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.
Fo more, see EPA references on criteria air pollutants.
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 |
Lead (Pb) |
| Quarterly Average |
|
1.5 µg/m3 |
Primary & Secondary |
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 |
Particulate < 10 micrometers (PM-10) |
| Annual Arithmetic Mean |
|
50 µg/m3 |
Primary & Secondary |
| 24-hour Average |
|
150 µg/m3 |
Primary & Secondary |
Particulate < 2.5 micrometers (PM-2.5) |
| 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 |
|
| * The ozone 1-hour standard applies only to areas that were designated
nonattainment when the ozone 8-hour standard was adopted in July 1997.
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