Table 1. WHO guideline values on ambient air quality, 201610.
| Contaminant | Annual limit | Daily limit |
|---|---|---|
| PM2.5 | 10 μg/m3 annual mean | 25 μg/m3 24-hour mean |
| PM10 | 20 μg/m3 annual mean | 50 μg/m3 24-hour mean |
| NO2 | 40 μg/m3 annual mean | 200 μg/m3 1-hour mean |
| SO2 | ND | 20 μg/m3 24-hour mean |
| O3 | ND | 100 μg/m3 8-hour mean |
ND: not determined; NO2: nitrogen dioxide; O3: ozone; PM2.5: fine particulate matter less than or equal to 2.5 μm in diameter; PM10: coarse particulate matter with a diameter between 2.5 and 10 μm; SO2: sulfur dioxide; WHO: World Health Organization.