AirNow is a one-stop source for air quality data. AirNow reports air quality using the official U.S. Air Quality Index (AQI), a color-coded index designed to communicate whether air quality is healthy or unhealthy.

The AQI is calculated for four major air pollutants regulated by the Clean Air Act: ground level ozone, particle pollution, carbon monoxide, and sulfur dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health. Of these, ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health.

AirNow is a partnership of the EPA, NOAA, National Park Service, NASA, Centers for Disease Control, and tribal, state, and local air quality agencies.