Based on the air quality monitoring results, the area can be classified into the following categories.
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Attainment Area: An area considered to have air quality that meets or exceeds the United States Environmental Protection Agency’s health standards used in the Clean Air Act. An area may be an attainment area for one pollutant and a non-attainment area for others.
- Maintenance Area: Any geographic region of the United States previously designated non-attainment pursuant to the Clean Air Act amendments of 1990 and subsequently redesignated to attainment subject to requirement to develop a maintenance plan.
- Non-Attainment Area: Any geographic region of the United States that has been designated as non-attainment for any pollutant for which a National Ambient Air Quality Standard (NAAQS) exists. The non-attainment designation identifies the area as an area where pollution levels have exceeded those standards prescribed by the EPA. The designation requires that those areas designated as such implement strategies to improve air quality or risk losing funding.
Guilford and Davidson Counties were originally declared non-attainment for ozone (O3) on January 6, 1992. At that time, Guilford and Davidson Counties were classified as moderate non-attainment. On November 8, 1993, both counties were redesignated to maintenance for ozone.