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A woman wearing a face mask walks in heavy smog in Harbin, northeast China's Heilongjiang province, on October 21, 2013. Choking clouds of pollution blanketed Harbin, a Chinese city famed for its annual ice festival on October 21, reports said, cutting visibility to 10 metres (33 feet) and underscoring the nation's environmental challenges.   CHINA OUT     AFP PHOTO        (Photo credit should read STR/AFP/Getty Images)
A woman wearing a face mask walks in heavy smog in Harbin, northeast China's Heilongjiang province, on October 21, 2013. Choking clouds of pollution blanketed Harbin, a Chinese city famed for its annual ice festival on October 21, reports said, cutting visibility to 10 metres (33 feet) and underscoring the nation's environmental challenges.   CHINA OUT     AFP PHOTO        (Photo credit should read STR/AFP/Getty Images)

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    How deadly is air pollution?

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How deadly is air pollution?

Air pollution increases the risk of heart disease, strokes and lung cancer, causing millions of deaths every year.

How deadly is air pollution?

Air pollution increases the risk of heart disease, strokes and lung cancer, causing millions of deaths every year.