National Ambient Air Quality Standards
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Counties in the United States where one or more National Ambient Air Quality Standards are not met, as of June 2007.
Counties in the United States where one or more National Ambient Air Quality Standards are not met, as of June 2007.

The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency that apply for outdoor air throughout the country. Primary standards are designed to protect human health, with an adequate margin of safety, including sensitive populations such as children, the elderly, and individuals suffering from respiratory disease. Secondary standards are designed to protect public welfare from any known or anticipated adverse effects of a pollutant (e.g. building facades, visibility, crops, and domestic animals).

NAAQS requires the EPA to set standards on six criteria air contaminants:

  1. Ozone (O3)
  2. Particulate Matter
    • PM10, coarse particles: 2.5 micrometers (μm) to 10 μm in size (although current implementation includes all particles 10 μg or less in the standard)
    • PM2.5, fine particles: 2.5 μm in size or less
  3. Carbon monoxide (CO)
  4. Sulfur dioxide (SO2)
  5. Nitrogen oxides (NOx)
  6. Lead (Pb)

Standards

The standards are listed in Title 40 of the Code of Federal Regulations Part 50.

content
Pollutant Type Standard Averaging Timea Regulatory Citation
SO2 Primary 0.14 ppm (365 μg/m3) 24-hour 40 CFR 50.4(b)
SO2 Primary 0.030 ppm (80 μg/m³) annual 40 CFR 50.4(a)
SO2 Secondary 0.5 ppm (1,300 μg/m³) 3-hour 40 CFR 50.5(a)
PM10 Primary and Secondary 150 μg/m³ 24-hour 40 CFR 50.6(a)
PM2.5 Primary and Secondary 35 μg/m³ 24-hour 40 CFR 50.7(a)
PM2.5 Primary and Secondary 15 μg/m³ annual 40 CFR 50.7(a)
CO Primary 35 ppm (40 mg/m³) 1-hour 40 CFR 50.8(a)(2)
CO Primary 9 ppm (10 mg/m³) 8-hour 40 CFR 50.8(a)(1)
O3 Primary and Secondary 0.12 ppm (235 μg/m³) 1-hourb 40 CFR 50.9(a)
O3 Primary and Secondary 0.075 ppm (235 μg/m³) 8-hour 40 CFR 50.10(a)
NO2 Primary and Secondary 0.053 ppm (100 μg/m³) annual 40 CFR 50.11(a) and (b)
Pb Primary and Secondary 1.5 μg/m³ quarterly 40 CFR 50.12

Note a: Each standard has its own criteria for how many times it may be exceeded, in some cases using a three year average.

Note b: As of June 15, 2005, the 1-hour ozone standard no longer applies to areas designated with respect to the 8-hour ozone standard (which includes most of the United States, except for portions of 10 states).

Source: USEPA

See also

External links
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