Keep track of the most polluted cities in the world with our air quality index … The air quality index is not a tool for checking compliance with air quality standards and cannot be used for this purpose. Air Quality Index (AQI) Calculation The Air Quality Index is based on measurement of particulate matter (PM 2.5 and PM 10), Ozone (O 3), Nitrogen Dioxide (NO 2), Sulfur Dioxide (SO 2) and Carbon Monoxide (CO) emissions.Most of the stations on the map are monitoring both PM 2.5 and PM 10 data, but there are few exceptions where only PM 10 is available. Methodology The Index uses ‘up-to-date’ air quality data officially reported every hour by EEA member countries, complemented where necessary by modelled air quality data from the European Union’s Copernicus Atmosphere Monitoring Service (CAMS).