A simple air quality index (AQI) was introduced for the Helsinki Metropolitan Area in 1993, in order to inform the public about the current air quality in an easily understood way. The pollutants included in the AQI are CO (1 and 8 h), NO2 (1 and 24 h), SO2 (1 and 24 h), O-3 (1 h) and PM10 (24 h). The AQI is linked to the new air quality guidelines in Finland. The AQI is based on acute health effects, but longterm effects on nature and materials are also taken into consideration. Subindices are calculated hourly for all pollutants and for a given hour the highest subindex becomes the AQI. AQI values are currently calculated for the center of Helsinki and for typical suburban areas.
