Air quality index

Air quality index

Air quality index is used to describe the air quality in simple terms and an easy-to-understand color scale. It is based on hourly means of pollutant concentrations and gives an overall characterisation of the actual air quality.

The index takes into account the concentrations of sulphur dioxide (SO2), nitrogen dioxide (NO2), respirable particles (PM10), fine particles (PM2,5), ozone (O3) and carbon monoxide (CO). The measured concentrations are compared with the current air quality guidelines.

This air quality index has been developed in Common Information to European Air (CITEAIR) projects funded by the European Union (

Color codes corresponding to the concentration levels

SO2 NO2 PM10 PM2.5 O3 CO
Very high 500- 400- 180- 110- 240- 20-
High 350-500 200-400 90-180 55-110 180-240 10-20
Medium 100-350 100-200 50-90 30-55 120-180 7.5-10
Low 50-100 50-100 25-50 15-30 60-120 5-7.5
Very low 0-50 0-50 0-25 0-15 0-60 0-5

Concentrations are in µg/m3 except for CO in mg/m3