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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 (mg/m3). Click here for description of pollutants listed below.

National Ambient Air Quality Standards
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 0.075 ppm    (150 µg/m3) Primary & Secondary
Lead (Pb)
    Rolling Three Month Average 0.15 µg/m3 Primary & Secondary
Fine Particulate (PM2.5)
    Annual Arithmetic Mean 15 µg/m3 Primary & Secondary
    24-hour Average 35 µg/m3 Primary & Secondary
Particulate (PM10)
    Annual Arithmetic Mean 50 µg/m3 Primary & Secondary
    24-hour Average 150 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

*Parenthetical value is approximately equivalent concentration.


VT DEC Air Quality & Climate Division Davis Building 2nd Floor, 1 National Life Drive   Montpelier, VT  05620-3802  Tele: 802-828-1288 Fax: 802-828-1250

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