The Air Pollution Index (API) is a simple and generalized way to describe the air quality, which is used in Malaysia. It is calculated from several sets of air pollution data. It was formerly used in mainland China and Hong Kong. In mainland China the API was replaced by an updated Air Quality Index in early 2012 and on 30 December 2013 Hong Kong moved to a health based index.

An air quality index (AQI) is a number used by government agencies  to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects. Different countries have their own air quality indices, corresponding to different national air quality standards. Some of these are the Air Quality Health Index (Canada), the Air Pollution Index (Malaysia), and the Pollutant Standards Index (Singapore).