12. WHO Air Quality Guidelines Reference

Pollutant	Averaging Period	WHO 2021 Guideline Level
PM2.5	Annual Mean	5 μg/m³
PM2.5	24-hour Mean	15 μg/m³
PM10	Annual Mean	15 μg/m³
PM10	24-hour Mean	45 μg/m³

Most African cities substantially exceed WHO guidelines, with annual PM2.5 often 5–10 times the guideline level. WHO also provides interim targets (IT1–IT4) for countries working progressively toward guideline levels. Evidence shows health effects occur at concentrations below these guidelines, with no apparent safe threshold.