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 measured air quality data and gives an overall characterization of the actual air quality. Finnish air quality index is a hourly index which describes the air quality today, based on hourly values and updated every hour.

ColorAir qualityHealth impactsOther long term impacts
goodno known impactsmild environmental impacts
satisfactoryvery unlikelymild environmental impacts
fairunlikelyclear impacts in vegetation and materials
poorsensitive individuals may experience adverse effectsclear impacts in vegetation and materials
very poorsensitive population may experience adverse effectsclear impacts in vegetation and materials

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

Sub-index definitions

A sub-index is assigned for each of the measured compounds and the highest sub-index determines the overall air quality index at the station. So far, black carbon (BC) is not taken into account when determining the overall index.

Index values of the different compounds (sub-indexes), concentration micrograms per cubic meter air (µg/m3)
Index classification SO2 NO2 PM10 PM2.5 O3 BC TRS
good below 20 below 40 below 20 below 10 below 60 below 1 below 5
satisfactory 20-80 40-70 20-50 10-25 60-100 1-3 5-10
fair 80-250 70-150 50-100 25-50 100-140 3-7 10-20
poor 250-350 150-200 100-200 50-75 140-180 7-12 20-50
very poor above 350 above 200 above 200 above 75 above 180 above 12 above 50

The air quality index in use in Finland is developed and maintained by the Helsinki Region Environmental Services Authority HSY and the National Institute for Health and Welfare THL. The corresponding classification of black carbon (BC) has been developed in the EU-funded HOPE project.