image: Some major cities have made efforts to reduce air pollution, but the results are often not sufficient or long-lasting enough to mitigate health problems associated with air pollution. This material relates to a special issue of Science, "Urban Planet," that includes two Reviews, six Perspectives, and a series of new stories that feature the wide range of challenges from and impacts of an increasingly urbanized world. It appeared in the May 20, 2016 issue of Science, published by AAAS. view more
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