After EPA sets a new National Ambient Air Quality Standard (NAAQS) or revises an existing standard, the Clean Air Act requires the agency to designate areas in the United States as "attainment" (meeting),  "nonattainment" (not meeting) or “unclassifiable” (insufficient data). This website provides information on the process EPA, the states, and the tribes follow to designate areas for the health-based nitrogen dioxide standard established in 2010.