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An area is classified or designated as being in attainment if air quality monitoring indicates that the area is meeting National Ambient Air Quality Standards (NAAQS). NAAQS are set by the United States Environmental Protection Agency (U.S. EPA) and are required by the federal Clean Air Act (CAA) in order to protect human health and the environment. Ambient air in Indiana is closely monitored to be sure that NAAQS are being met. An area can be flagged for designation to nonattainment if air monitoring over a period of time indicates that there are more pollutants in the air than the NAAQS allow or if the area contributes air pollutants to a neighboring area where NAAQS are being exceeded. An area can be redesignated from nonattainment to attainment if the area has monitored attainment of the air quality standard and U.S. EPA has determined that the improvement in air quality is due to permanent and enforceable reductions in emissions, among other requirements.