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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 (g/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 g/m3) Primary & Secondary

Ozone (O3)
    1-hour Average 0.12 ppm (235 g/m3) Primary & Secondary
    8-hour Average 0.08 ppm (157 g/m3) Primary & Secondary

Lead (Pb)
    Quarterly Average 1.5 g/m3   Primary & Secondary

Particulate (PM 10)       Particles with diameters of 10 micrometers or less
    Annual Arithmetic Mean 50 g/m3   Primary & Secondary
    24-hour Average 150 g/m3   Primary & Secondary

Particulate (PM 2.5)       Particles with diameters of 2.5 micrometers or less
    Annual Arithmetic Mean 15 g/m3   Primary & Secondary
    24-hour Average 65 g/m3   Primary & Secondary

Sulfur Dioxide (SO2)
    Annual Arithmetic Mean 0.030 ppm (80 g/m3) Primary
    24-hour Average 0.14 ppm (365 g/m3) Primary
    3-hour Average 0.50 ppm (1300 g/m3) Secondary
* Parenthetical value is an approximately equivalent concentration.

 

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