TABLE 1

European Union (EU) reference values and World Health Organization (WHO) air quality guidelines (AQGs) for the main air pollutants [22]

EU reference valueWHO AQGs
PM2.525 µg·m−3 annual mean10 µg·m−3 annual mean
25 µg·m−3 24-h mean
PM1040 µg·m−3 annual mean
50 µg·m−3 24-h mean (not to be exceeded on >35 days per year)
20 µg·m−3 annual mean
50 µg·m−3 24-h mean
NO240 µg·m−3 annual mean
200 µg·m−3 1-h mean
40 µg·m−3 annual mean
200 µg·m−3 1-h mean
O3120 µg·m−3 8-h mean100 µg·m−3 8-h mean
SO2125 µg·m−3 24-h mean (not to be exceeded on >3 days per year)20 µg·m−3 24-h mean
500 µg·m−3 10-min mean
BaP1 ng·m−3 annual mean

PMx: particles with a 50% cut-off aerodynamic diameter of x µm; NO2: nitrogen dioxide; O3: ozone; SO2: sulfur dioxide; BaP: benzo[a]pyrene.