An Air Quality Index (AQI) is an index for reporting daily air quality that is a number (e.g. UK: the index is numbered 1 (low) ~ 10 (very high) and divided into four bands, USA: the index is numbered 0 (good) ~ 500 (hazardous) and divided into six bands) used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulphur dioxide, and nitrogen dioxide.