Cyclists in Zhengzhou wear masks, while riding along a road in heavy smog. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A tour boat sails through heavy smog in Suzhou, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A man does morning exercises in heavy smog in Dezhou,China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A train travels along a bridge in heavy smog in Beijing, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A man does morning exercises at a park in heavy smog in Wenxian, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A woman poses for photos in heavy smog in Suzhou, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A salesman dressed as Santa Claus wears a mask in heavy smog in Jinan, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A dog wearing a mask and his owner walk along a road in heavy smog in Hangzhou, China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
Heavy smog blankets Donggang CBD in Dalian, which is located in northeast China's Liaoning Province. (Photo via Xinhua/Wang Hua via Getty Images)
Vehicles run in heavy smog in Shijiazhuang, Hebei Province of China. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)
A Chinese paramilitary policeman wearing a mask guards Beijing's Tiananmen Square. (Photo by ChinaFotoPress/ChinaFotoPress via Getty Images)