The Clean Air Act requires the United States Environmental Protection Agency (U.S. EPA) to set National Ambient Air Quality Standards (NAAQS) for pollutants that cause or contribute to air pollution which may reasonably be anticipated to endanger public health and welfare. The U.S. EPA has set NAAQS for the six criteria pollutants (carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2)).
Nonattainment areas are designated regions within the country where measured concentrations of one or more criteria pollutant exceeds the NAAQS or contribute significant amounts of pollutants to an area that measures air quality that exceeds the standard. If a state has nonattainment areas within its borders, the state must submit a state implementation plan (SIP) to U.S. EPA detailing steps necessary to achieve the standard. Nonattainment areas which are later redesignated to attainment are considered maintenance areas.
Since establishing the first NAAQS in the 1970s, U.S. EPA has continued to conduct periodic reviews and adopt appropriate revisions. U.S. EPA’s NAAQS Table provides the current standards for each criteria pollutant, as well as links to historical timelines showing specific changes over the years. Following is information concerning the current and historical nonattainment status for Indiana’s counties under previous and current NAAQS.
Information by NAAQS
- Carbon Monoxide
- Nitrogen Dioxide
- Particulate Matter
- Sulfur Dioxide