The world’s most comprehensive air pollution database has been updated again, mapping out a picture of a global health crisis that is disparate, changing and in some places just obscure. Compiled by the World Health Organisation (WHO), the statistics on 4,300 cities reveal annual levels of particulate matter, miniscule particles in the air that
India is home to the world’s most toxic cities. Beijing is no longer the global symbol of smog it once was. And there is a staggering lack of air quality monitoring in some countries.