WHO Air quality standards worldwide 2005-2021, by pollutant
The latest World Health Organization (WHO) Air Quality guidelines (AQG) recommend that annual average concentrations of PM2.5 should not exceed five micrograms per cubic meter (μg/m3). However, annual average PM2.5 levels in major global cities, such as Mumbai, Beijing, and Cairo, are often far higher than the recommended limit.
The new PM2.5 AQG is an improvement from the previous limit of 10 μg/m3 in 2005. Average annual nitrogen dioxide guidelines have also become stricter since 2005, falling from 40 μg/m3 to 10 μg/m3.