Attainment Status of National Ambient Air Quality Standards What are the NAAQS? The Clean Air Act defines six principal pollutants as the Criteria Air Pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ground-level ozone (O3), particulate matter (PM2.5 and PM10), and sulfur dioxide (SO2). The National Ambient Air Quality Standards (NAAQS) are set by the U.S. Environmental Protection Agency to protect public health and the environment. These standards set allowable levels of each criteria air pollutant in ambient (outdoor) air. The EPA periodically reviews the NAAQS and may revise them as provided in law. Areas of the nation that meet the NAAQS are attainment areas, while areas that exceed one or more NAAQS are nonattainment areas. The EPA requires states to establish additional air quality planning measures to bring nonattainment areas into attainment. North Carolina Attainment Status Since 2015, all areas of North Carolina are in attainment with all federal NAAQS. Pollutant Standard Attainment Nonattainment Counties Ozone 0.070 ppm 8-hour average (2015 standard) None Lead 0.15 μg/m3 rolling 3-month average (2008 standard) None Particulate Matter (PM2.5) 12.0 μg/m3 1-year average (2012 standard) None 12.0 μg/m3 1-year average (2012 standard) None 35 μg/m3 24-hour average (2012 standard) None Particulate Matter (PM10) 150 μg/m3 24-hour average (2012 standard) None Carbon Monoxide 9 ppm 8-hour average (1971 standard) None 35 ppm 1-hour average (1971 standard) None Nitrogen Dioxide 100 ppb 1-hour standard (2010 standard) None 53 ppb 1-year average (1971 standard) None Sulfur Dioxide 75 ppb 1-hour average (2010 standard) None 0.5 ppm 3-hour average (1971 standard) None Updated Aug. 2022 North Carolina Attainment History North Carolina has made tremendous progress in recent decades toward improving air quality by reaching full attainment with all NAAQS across the entire state. In the past, certain areas of North Carolina were designated nonattainment for ozone, PM2.5, carbon monoxide or sulfur dioxide. The below pages have information on those nonattainment designation and the State Implementation Plans that led to eventual attainment. Ozone Designation History Particulate Matter 2.5 Designation History Sulfur Dioxide Designation History Carbon Monoxide Designation History Early Action Compact Archived information about the North Carolina Early Action Compact efforts are available on this webpage.