The National Ambient Air Quality Standards are the Environmental Protection Agency’s limits on the amount of the seven criteria pollutants that are permissible in the ambient air. The primary standard is human health-based; the secondary standard is environmentally-based. The environmentally-based secondary standards prevent damage to crops, animals, vegetation, and buildings.
The Clean Air Act requires that each pollutant’s standards be reviewed against the latest health-based information every five years to determine if the standards need to change to protect human health with an adequate margin of safety for sensitive populations (children, elderly and individuals suffering from respiratory or heart disease).
National Ambient Air Quality Standards
| |
Primary Standards |
Secondary Standards |
| Pollutant |
Level |
Averaging Time |
Level |
Averaging Time |
Carbon Monoxide
(CO) |
9 ppm
(10 mg/m3) |
8-hour |
None |
35 ppm
(40 mg/m3) |
1-hour |
Lead
(Pb) |
0.15 µg/m3 |
Rolling 3-month Average |
Same as Primary |
Nitrogen Dioxide
(NO2) |
53 ppb |
Annual
(Arithmetic Average) |
Same as Primary |
| 100 ppb |
1-hour |
None |
Particulate Matter < 10 µm
(PM10) |
150 µg/m3 |
24-hour |
Same as Primary |
Particulate Matter < 2.5 µm
(PM2.5) |
15.0 µg/m3 |
Annual
(Arithmetic Average) |
Same as Primary |
| 35 µg/m3 |
24-hour |
Same as Primary |
Ozone
(O3) |
0.075 ppm
(2008 Standard) |
8-hour |
Same as Primary |
0.08 ppm
(1997 Standard) |
Same as Primary |
| 0.12 ppm |
1-hour |
Same as Primary |
Sulfur Dioxide
(SO2) |
0.03 ppm |
Annual
(Arithmetic Average) |
0.5 ppm |
3-hour |
| 0.14 ppm |
24-hour |
| 75 ppb |
1-hour |
None |
|
| Current as of April 19, 2011. Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb - 1 part in 1,000,000,000) by volume, milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3). |
|
For more information about the NAAQS, go to www.epa.gov/air/criteria.html.