Air pollution can have a dramatic impact on human health and well being. When air pollutants are above certain levels, they are considered harmful to health and the environment. For example, they are associated with aggravation of asthma, premature death from heart and lung diseases, and increased acid conditions in lakes and streams. The federal Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to identify air pollutants that pose a risk to the public health and welfare and set standards indicating the permissible air concentration of each one. EPA has identified six pollutants of concern: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2). These pollutants are referred to as “criteria pollutants” since EPA develops criteria, or science-based guidelines, for them when it sets standards. EPA sets primary and secondary standards for the pollutants. Primary standards take into consideration the human health impact of the pollutant, while secondary ones consider the impact on public welfare, which includes damage to crops, wildlife, buildings, and visibility.
Once EPA sets a standard for a pollutant, it designates individual counties and multi-county metropolitan areas of a state as nonattainment, attainment, or maintenance for the standard. Nonattainment means that the county and/or area is not meeting the standard, while attainment means that it is. Maintenance means that it has only more recently begun to meet the standard and must continue to provide EPA with information showing that it is maintaining the standard, before the area can qualify for redesignation as attainment. For each area that is nonattainment for one standard, state and local air quality management agencies must develop a specific plan to attain the standard. The plan is a State Implementation Plan (SIP) and includes many kinds of information, such as regulations for reducing emissions of the pollutant and the levels of emissions from various sources.
|
Pollutant
|
Averaging
Time
|
Standard
Concentration
|
|
Carbon Monoxide
(CO)
|
8-Hour
(1985 std)
|
9 ppm
(10 mg/m3)
|
|
Lead
(Pb)
|
Rolling 3-Month Average
(2008 std.)
|
0.15 µg/m3
|
|
Nitrogen Dioxide
(NO2)
|
Annual
(1985 std.)
|
53 ppb
(100 µg/m3)
|
|
Ozone
(O3)
|
1-Hour
(1997 std. Revoked)
|
125 ppb
|
|
8-Hour
(1997 std.)
|
85 ppb
|
|
Particulate Matter
(PM10)
|
24-Hour
(1987 std.)
|
150 µg/m3
|
|
Annual
(1997 std. Revoked)
|
50 µg/m3
|
|
Particulate Matter
(PM2.5)
|
24-Hour
(2006 std.)
|
35 µg/m3
|
|
Annual
(1997 std.)
|
15 µg/m3
|
|
Sulfur Dioxide
(SO2)
|
24 Hour
(1996 std.)
|
140 ppb
(365 µg/m3)
|
|
Annual
(1996 std.)
|
30 ppb
(80 µg/m3)
|
|
3-Hour
(1996 std.)
|
500 ppb
(1300 µg/m3)
|
