A numerical index used for reporting severity of ambient air pollution levels to the public. The air quality index (AQI) currently incorporates five criteria pollutants (ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide) into a single index. The AQI also incorporates the 8-hour ozone standard and the 24-hour PM2.5 standard into the index calculation. AQI ranges from 0 (good air quality) to 500 (hazardous air quality). The index number increases as air pollution increases, increasing the likelihood of health effects.