POLLUTION LOCATOR|National Ambient Air Quality Standards

The Clean Air Act requires the EPA to establish National Ambient Air Quality Standards (NAAQS) for six pollutants considered harmful to public health and the environment: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. The standards were set at the level required to provide an ample margin of safety to protect the public health. The six pollutants were chosen based on two criteria:
(1) Emissions cause or contribute to air pollution that may reasonably be anticipated to endanger public health or welfare; and
(2) Presence in the ambient air results from numerous or diverse mobile or stationary sources.

The Clean Air Act established two types of national air quality standards. Primary standards are intended 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.

Fo more, see EPA references on criteria air pollutants.

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

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

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

Particulate < 10 micrometers (PM-10)
    Annual Arithmetic Mean   50 µg/m3 Primary & Secondary
    24-hour Average   150 µg/m3 Primary & Secondary

Particulate < 2.5 micrometers (PM-2.5)
    Annual Arithmetic Mean   15 µg/m3 Primary & Secondary
    24-hour Average   65 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
* The ozone 1-hour standard applies only to areas that were designated nonattainment when the ozone 8-hour standard was adopted in July 1997.