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.

Color	Air quality	Health impacts	Other long term impacts
green	good	no known impacts	mild environmental impacts
yellow	satisfactory	very unlikely	mild environmental impacts
orange	fair	unlikely	clear impacts in vegetation and materials
red	poor	sensitive individuals may experience adverse effects	clear impacts in vegetation and materials
purple	very poor	sensitive population may experience adverse effects	clear 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	PM_2.5	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.