Health Standards (NAAQS)

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
9 ppm
(10 mg/m3)
8-hour None
35 ppm
(40 mg/m3)
0.15 µg/m3 Rolling 3-month Average Same as Primary
Nitrogen Dioxide
53 ppb Annual
(Arithmetic Average)
Same as Primary
100 ppb 1-hour None
Particulate Matter < 10 µm
150 µg/m3 24-hour Same as Primary
Particulate Matter < 2.5 µm
15.0 µg/m3 Annual
(Arithmetic Average)
Same as Primary
35 µg/m3 24-hour Same as Primary
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
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