National Ambient Air Quality Standards

From Wikipedia, the free encyclopedia

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, including sensitive populations such as children, the elderly, and individuals suffering from respiratory disease. Secondary standards are designed to protect public welfare (e.g. building facades, visibility, crops, and domestic animals).

NAAQS requires the EPA to set standards on six criteria pollutants:

  1. Ozone (O3)
  2. Particulate Matter
    • PM10, course 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)

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 0.08 ppm (235 μg/m3) 8-hour 40 CFR 50.10(a)
NOx 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

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