Harmful air pollution now affects 99 per cent of everyone on Earth

Adam Vaughan is a writer.

Almost everyone on Earth lives in areas with harmful levels of air pollution. The official figure is that 99 percent of the world's population is affected, up from 90 percent four years ago.

Nine of the world's 10 cities have the worst air pollution caused by a pollutant called PM 2.5. A new database published by the WHO shows that Delhi is in third place. Settlements in India, Iran, Iraq, Pakistan, South Africa and Saudi Arabia make up the top 10 list of the dirtiest places.

Fossil fuel burning in cars and power plants is one of the causes of both pollutants. Chinese cities, which previously dominated lists of the world's most polluted urban areas, have cleaned up their air considerably. Beijing is the most polluted city in the world, but it still has high annual levels of PM 2.5.

The urgent need to address the twin health challenges of air pollution and climate change underscore the pressing need to move faster towards a world that is.

Low and middle-income countries are more affected by PM than the global average. The economic split is less clear for a third pollutant, nitrogen dioxide.

Although they aren't legally binding, the WHO updated its guidelines for air pollution limits last September. There are no standards for PM in South-East Asia and the Middle East and northern Africa according to the new database update. Only 13 per cent of European settlements are compliant, compared to 23 per cent in the Americas.

The average population of settlements in the database is almost half a million.