Quantifying the magnitude of those impacts in cities worldwide, however, presents considerable challenges due to limited information on both health effects and air pollution exposures in many parts of the world. Man-made outdoor air pollution in the world’s cities, derived largely from combustion processes, is a complex mixture with many toxic components. We indexed this mixture in terms of particulate matter (PM), a component that has been consistently linked with serious health effects and, importantly, that can be estimated worldwide. Exposure to PM has been associated with a wide range of health effects, but its effects on mortality are arguably the most important, and are also most amenable.
