BEIJING, CHINA - MARCH 27: A genernal view of Chang'an Avenue blanketed in smog on March 27, 2014 in Beijing, China. An estimated 7 million people die worldwide every year due to air pollution, both indoor and outdoor, and it is now the "single largest environmental health risk", according to a report by the UN World Health Organization (WHO). The reports findings suggested a link between air pollution and heart disease, respiratory problems and cancer, listing it as the cause of about one in eight deaths worldwide. (Photo by Xiao Lu Chu/Getty Images)
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Getty Images News Xiaolu Chu