dioxide in the city air is due to exhaust gases from traffic. The abbreviation NO2 refers to nitrogen
are high if the hourly value exceeds 150 µg/m3. The limit for the hourly value is 200 µg/m3 and the threshold value is
400 µg/m3. These values are very rarely
exceeded in the Helsinki Metropolitan Area and when they are exceeded, the
situation will be dealt through a contingency plan. On the annual level,
concentrations are high and the limit value of 40 µg/m3 is exceeded in the city
centre of Helsinki and along the heavily trafficked routes.