PerspectiveClimate Change

Clean Air for Megacities

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Science  30 Oct 2009:
Vol. 326, Issue 5953, pp. 674-675
DOI: 10.1126/science.1176064

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As of 2008, over half of humanity lives in cities. The number of megacities (with populations over 10 million) grew from 3 in 1975 to 19 in 2007, and is projected to increase to 27 in 2025 (1). These megacities are the engines of growing economies, but are also very large sources of air pollutants and climate-forcing agents. The growth of megacities greatly aggravates the health impacts of polluted air, yet it may also provide an opportunity to mitigate climate change, if implemented air quality policies are designed to also reduce global warming.