National ambient a
National ambient air
The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency under authority of the Clean Air Act (42 U.S.C. 7401 et seq.) 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 diseases. Secondary standards are designed to protect public welfare from any known or anticipated adverse effects of a pollutant. A district meeting a given standard is known as an "attainment area" for that standard, and otherwise a "non-attainment area"
standards
The standards are listed in Title 40 of the Code of Federal Regulations Part 50.
| 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 (150 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 | 0.15 μg/m³ | Rolling 3 months | 40 CFR 50.12 |
- ^a Each standard has its own criteria for how many times it may be exceeded, in some cases using a three year average.
- ^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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