What are PM2.5 pollutantsPM2.5 refers to fine particles that have a diameter of 2.5 micrometers or less. These tiny, light, and inhalable pollutants can stay in the air for long periods of time and are a major risk to human health when concentrations are high. The World Health Organization advises that annual mean PM2.5 concentrations should not exceed 10 µg/m3. Major sources of PM2.5 include solid waste burning, road vehicles, and power plants.
Pollution in citiesIn 2021, Delhi was yet again the most polluted capital city in the world with an average PM2.5 concentration of 85 µg/m3. This was followed by the Bangladesh capital, Dhaka.
In 2020, many cities around the world experienced reductions in PM2.5 concentrations due to COVID-19 lockdowns and restrictions, with levels in Delhi falling roughly 15 percent compared with the previous year.