Attainment area
Attainment area means any geographic area in which levels of a given criteria air pollutant (e.g., ozone, carbon monoxide, PM10, PM2.5, and nitrogen dioxide) meet the health-based National Ambient Air Quality Standards (NAAQS) for that pollutant. An area may be an attainment area for one pollutant and a nonattainment area for others. A maintenance area (see definition below) is not considered an attainment area for transportation planning purposes.
Source
23 CFR § 450.104
Scoping language
Unless otherwise specified, the definitions in 23 U.S.C. 101 and 49 U.S.C. 5302 are applicable to this part.