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 can lead to health conditions such as asthma, lung cancer or heart disease.





The data is collected from multiple, variable sources and in some places is just not available, so with these caveats in mind, this is what we learned:



