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
Read more about this topic: National Ambient Air Quality Standards
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—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
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