Global studies of the health impacts of fine particulate matter (PM2.5) have been based on particle mass, but there is evolving evidence indicating that adverse health effects can vary depending on the source and composition of PM2.5.

Cities in India and China have become iconic for air pollution challenges and the health impacts they bring. But city-dwellers in India and China are not the only ones facing worrying levels of air pollution. From Senegal to Peru, millions of people breathe polluted air every day, suffering a range of health implications.