Pollutants | EU legal limits (averaging period) | WHO guidelines (averaging period) | Main sources |
Nitrogen dioxide (NO2) | 200 µg/m3 (1 hour) 40 µg/m3 (1 year) | 200 µg/m3 (1 hour) 40 µg/m3 (1 year) | Transport, combustion |
Ozone (O3) | 120 µg/m3 (8 hours) | 100 µg/m3 (8 hours) | Reaction of hydrocarbons, nitrogen oxides and volatile organic compounds in sunlight |
Particulate matter (PM10) | 50 µg/m3 (24 hours) 40 µg/m3 (1 year) | 50 µg/m3 (24 hours) 20 µg/m3 (1 year) | Transport (exhaust, tyre, brake wear), combustion, industrial processes and construction |
Particulate matter (PM2.5) | 25 µg/m3 (1 year) | 10 µg/m3 (24 hours) 25 µg/m3 (1 year) | |
Sulfur dioxide (SO2) | 350 µg/m3 (1 hour) 125 µg/m3 (24 hours) | 500 µg/m3 (10 min) 20 µg/m3 (24 hours) | Coal combustion and road transport |