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National Ambient Air Quality Standards
Under the federal Clean Air Act, the U.S. Environmental Protection Agency has identified and set standards for six criteria air pollutants: ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, particulate matter, and lead. For each pollutant, a health-based or "primary" standard has been set to protect public health in general and a welfare-based or "secondary" standard has been set to protect quality of life and the environment. Pollutants may have short-term standards to protect against acute or high dose exposures and/or longer-term standards to protect against chronic or extended exposures. The values listed in the table below are based on an average dose measured over the time period listed.
(New Hampshire Ambient Air Quality Standards Rule)
| National Ambient Air Quality Standards |
| Pollutant |
Primary Standard |
Secondary Standard |
Regulation Allowance |
| Ozone (O3)1 |
1-hour average conc.:
0.120 ppm
8-hour average conc.:
0.075 ppm
|
Same as primary
Same as primary
|
Not to exceed more than one per year over 3-year average 3-year average of the annual 4th highest daily maximum concentration at or below the standard |
| Carbon Monoxide (CO) |
8-hour average conc.:
9 ppm
|
N/A |
Not to be exceeded more than once per year |
1-hour average conc.:
35 ppm
|
N/A |
Not to be exceeded more than once per year |
Nitrogen Dioxide
(NO2) |
Annual Arithmetic Mean:
100 µg/m3
|
Same as primary
|
|
Particulate
Matter (PM10)2
|
24-hour conc.:
150 µg/m3
|
Same as primary
|
3-year average of 99th percentile conc. at or below the standard3
|
Annual Arithmetic Mean:
50 µg/m3
|
Same as primary
|
3-year average at or below the standard |
Particulate
Matter (PM2.5)3
|
24-hour average conc.: 35 µg/m3
|
Same as primary
|
3-year average of 98th percentile conc. at or below the standard
|
Annual Arithmetic Mean:
15 µg/m3
|
Same as primary
|
3-year average at or below the standard
|
| Sulfur Dioxide (SO2) |
Annual Arithmetic Mean:
0.03 ppm (80 µg/m3)
|
|
|
Maximum 24-hour conc.:
0.14 ppm (365 µg/m3) |
Maximum 3-Hour conc.:
1300 µg/m3
|
Not to be exceeded more than once per year
|
| Lead
|
Maximum Arithmetic Mean:
1.5 µg/m3
|
Same as primary
|
|
Abbreviations: ppm = parts per million; m g/m3
= micrograms per cubic meter
1Standard for ozone was revised in 1997 from a one-hour standard to an eight-hour standard. In 2005, the one-hour ozone standard was revoked, except in limited areas outside New Hampshire. In March 2008, EPA revised the eight-hour standard from 0.08ppm to 0.075ppm to be more protective of public health; implementation of the new standard is currently in transition.
2Standard for particulate matter was revised in 1987
from total suspended particulates (TSP) to PM10, a smaller particle
size of 10 micrometers or less in diameter.
3Standard for fine particulate matter (particle size of 2.5 micrometers or less in diameter) was added in 1997 and revised in 2006.
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