Air pollution kills seven million people a year, according to the WHO. This map shows about 50 of the worst cities for indoor and outdoor air pollution measured by the amount of particulate matter in the air. The WHO current interim target asks countries to aim for 70 on the scale shown on the map. For more on this neglected health threat, read our analysis here: http://www.irinnews.org/report/101285/killing-us-softly