Scorecard ranks states, counties, facilities, and air quality monitoring stations by the health risks, exposures, or emissions associated with each criteria air pollutant. Specific ranking criteria are defined below, with links to more information if you need it.

Note: Scorecard rankings are based on the most current data available, which varies for different ranking criteria. See Data Sources and Limits.

Ranking by health risks
Scorecard ranks states or counties by the number of person-days in exceedance of a criteria air pollutant's National Ambient Air Quality Standard. This measure indicates the number of people experiencing daily exceedances of Clean Air Act standards, and characterizes the magnitude of poor air quality conditions in an area.

Scorecard's exceedance rankings are based data from the U.S. EPA's Air Quality System database.

Ranking by exposures
Scorecard ranks counties or local air quality monitoring stations based on two measures of air quality:

First, Scorecard ranks areas based on the maximum AQI recorded. The Air Quality Index gives a single summary characterization of air quality. The AQI converts the measured pollutant concentrations of five criteria air pollutants in a community's air to a numerical scale of 0 to 500. The intervals on the AQI scale relate to the severity of potential health effects posed by air pollution levels. Levels above a AQI of 100 are considered unhealthful.

Scorecard also ranks counties or air quality monitoring stations based on peak concentrations recorded for specific criteria air pollutants. There are separate ranking options for each National Ambient Air Quality Standard, which define the maximum legally allowable pollutant concentration over an averaging period. Scorecard lets you rank based on all available averaging times for a pollutant. For example, you can rank on compliance with the 1-hr NAAQS for carbon monoxide of 35 ppm or the 8-hr standard of 9ppm.

Units of measure for the pollutant concentrations are parts per million (ppm) by volume or micrograms per cubic meter of air (µg/m3).

Scorecard's exposure rankings are based on monitoring data from the U.S. EPA's Air Quality System database.

Ranking by emissions
Scorecard ranks states or counties based on total annual missions of each criteria air pollutant, or by emissions from specific source categories (mobile, area, or point sources). Ozone-season daily average emissions data are provided for nitrogen oxides and volatile organic compounds because emissions of these ozone precursors cause more harm in the May to September ozone season than during other parts of the year.

Scorecard's emissions rankings are based on data from the U.S. EPA's National Emissions Trends database.