A flake of “black cloud” is seen in sky over Zhengzhou, capital city of Central China’s Henan province on September 8, 2015. The pollution zone like "advection fog" started to hang over the city from 6: 00 a.m. in Tuesday. (Photo/CFP)
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A flake of “black cloud” is seen in sky over Zhengzhou, capital city of Central China’s Henan province on September 8, 2015. The pollution zone like "advection fog" started to hang over the city from 6: 00 a.m. in Tuesday. (Photo/CFP)
