Table 2.

Limit concentration of each air pollutant according to the WHO and to the Lebanese Ministry of Environment

Outdoor air pollutants	WHO guidelines [12]	Lebanese Ministry of Environment averages [29]
NO2	40 μg/m3 annual mean 200 μg/m3 1-h mean	100 μg/m3 annual mean 150 μg/m3 24-h mean 200 μg/m3 1-h mean
SO2	20 μg/m3 24-h mean 500 μg/m3 10-min mean	80 μg/m3 annual mean 120 μg/m3 24-h mean 350 μg/m3 1-h mean
CO	10 mg/m3 8-h mean 30 mg/m3 1-h mean	10,000 μg/m3 8-h mean 30,000 μg/m3 1-h mean
O3	100 μg/m3 8-h mean	100 μg/m3 8-h mean 150 μg/m3 1-h mean
PM2.5	10 μg/m3 annual mean 25 μg/m3 24-h mean	–
PM10	20 μg/m3 annual mean 50 μg/m3 24-h mean	80 μg/m3 24-h mean