2014

From the dataset abstract

The material contains the air quality indices of HSY’s air quality monitoring sites on an hourly basis. The air quality index divides air quality into five different classes, from good to very poor. The index classes are based on the health effects of air pollutants and on standards. When the air quality is poor, sensitive people may develop symptoms.

The material is updated four times a year (March, June, September and December).

Source: Pääkaupunkiseudun ja muun Uudenmaan ilmanlaatuindeksit