Air Pollution in the Mega-cities

Health concerns related to air pollution in large cities have been voiced repeatedly over the last decades. This paper uses two approaches to describe particulate matter (PM) levels in 56 of the largest cities of the world. One is based on data from PM monitoring, collected from various sources by the World Health Organization. The other is based on the combination of atmospheric modelling, satellite remote sensing and surface monitoring data. According to both sources of information, at least 96 % of the populations of the large cities are exposed to PM 2.5 exceeding World Health Organization (WHO) Air Quality Guidelines levels. The cities with the highest PM concentrations and the lowest rates of air quality improvement over the past decade tend to be in countries at lower levels of economic development. Addressing local pollution sources, including transportation and solid fuel combustion for cooking and heating, may be effective in cleaning the air of the most polluted and less economically developed cities.