Scorecard's data on the concentration of criteria air pollutants in ambient air are derived from the Air Quality System (AQS) of EPA's AIRData website. The AQS database contains summary information of the criteria air pollutant concentration data collected by over 3,000 monitoring stations located in over 1,000 counties across the U.S.
State and local environmental agencies operate air monitoring sites, where equipment measures the concentration of air pollutants. The measurements are submitted to EPA for inclusion in the AIRDatabase. EPA summarizes the air pollution measurements from each monitoring site, providing information such as the highest values reported, the average value, and the number of values above National Ambient Air Quality Standards.