Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI)

This guidance is designed to aid local agencies in reporting air quality using the U.S. Air Quality Index as required in 40 CFR Part 58.50 and according to 40 CFR Appendix G to Part 58.

The AQI is EPA’s tool for communicating air quality. The AQI is divided into six categories that correspond to different levels of health concern. For ease of use, the categories are color-coded and provide statements about local air quality, which groups of people may be affected, and steps people can take to reduce their exposure to air pollution. The AQI is also used as the basis for air quality forecasts and current air quality reporting. EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act. Each of these pollutants has a national ambient air quality standard (NAAQS) set by EPA to protect public health:

• Ozone

• Particulate pollution (also called particulate matter)

• Carbon monoxide

• Nitrogen dioxide

• Sulfur dioxide

The AQI for each pollutant draws on the scientific information that supports the health-based NAAQS for that pollutant. The AQI value of 100 generally corresponds to an ambient air concentration that equals the level of the short-term NAAQS for protection of public health. AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is unhealthy: at first for certain sensitive groups of people, then for everyone as AQI values get higher. The AQI does not apply to hazardous air pollutants, extreme heat, and other aspects of outdoor air.