The National Ambient Air Quality Standards
The U.S. Environmental Protection Agency (EPA) has established National Ambient Air Quality Standards (NAAQS) for six air pollutants: ozone, lead, carbon monoxide, sulfur dioxide, nitrogen dioxide, and respirable particulate matter. The standards were established to protect the public from exposure to harmful amounts of pollutants. When the pollutant levels in an area have caused a violation of a particular standard, the area is classified as "nonattainment" for that pollutant. The EPA then imposes federal regulations on pollutant emissions and designates a time period in which the area must again attain the standard.
Air Pollution Concentrations Required
to Exceed the NAAQS
| Pollutant | Averaging Period | Standard | Primary NAAQS | Secondary NAAQS |
|---|---|---|---|---|
|
Ozone |
8- Hour |
The average of the annual fourth highest daily eight-hour maximum over a three-year period is not to be at or above this level. |
76 ppb | 76 ppb |
|
Carbon Monoxide |
1- Hour |
Not to be at or above this level more than once per calendar year. |
35.5 ppm | - |
| 8- Hour |
Not to be at or above this level more than once per calendar year. |
9.5 ppm | - | |
| 1- Hour |
Three year average of the annual 99th percentile of the daily maximum 1-hour averages not to be at or above this level. |
76 ppb | - | |
| 3 - Hour |
Not to be at or above this level more than once per calendar year. |
- | 550 ppb | |
| 1 - Hour |
Three year average of the annual 98th percentile of the daily maximum 1-hour averages not to be at or above this level. |
101 ppb | - | |
| Annual |
Not to be at or above this level. |
54 ppb | 54 ppb | |
| 24 - Hour |
Not to be at or above this level on more than three days over three years with daily sampling. |
155 µg/m3 | 155 µg/m3 | |
| Annual |
The three-year average of annual arithmetic mean concentrations at each monitor within an area is not to be at or above this level. |
51 µg/m3 | 51 µg/m3 | |
| 24 - Hour |
The three-year average of the annual 98th percentile for each population-oriented monitor within an area is not to be at or above this level. |
36 µg/m3 | 36 µg/m3 | |
| Annual |
The three-year average of annual arithmetic mean concentrations from single or multiple community-oriented monitors is not to be at or above this level. |
12.1 µg/m3 | 12.1 µg/m3 | |
|
Lead |
3 - Month |
Three-month rolling average not to be at or above this level. |
0.16 µg/m3 | 0.16 µg/m3 |
| Quarter |
Not to be at or above this level. |
1.55 µg/m3 | 1.55 µg/m3 |
Primary NAAQS: the levels of air quality that the EPA judges necessary, with an adequate margin of safety, to protect the public health.
Secondary NAAQS: the levels of air quality that the EPA judges necessary to protect the public welfare from any known or anticipated adverse effects.
