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National
Ambient Air Quality Standards (NAAQS)
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).
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 |
0.030 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 | |
| * Parenthetical value is an approximately equivalent
concentration. |
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