A picture made available 16 December 2016 shows a woman taking photos of lion sculptures that have their mouth covered by masks, on top of the stone hitching posts in Xi'an Fine Art College in Xi'an, Shaanxi province, China, 12 December 2016. Several art students spent an hour and a half in the night to putting masks on more than 800 stone hitching posts to raise awareness of air pollution. (Photo by EPA/Stringer)





People wearing masks stand in smog during a heavily polluted day in Beijing, China, December 17, 2016. (Photo by Reuters/China Daily)





Monks wearing masks walk at Tiananmen Square during a polluted day in Beijing, China, December 17, 2016. (Photo by Reuters/Stringer)





A man walks during sunrise in smog on a polluted day as a red alert issued for air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





People are seen on a street in smog during polluted day in Shenyang, Liaoning province, China, December 18, 2016. (Photo by Reuters/Stringer)





People sit on a bench at a park in heavy smog during a polluted day in Beijing, China, December 18, 2016. (Photo by Reuters/Stringer)





Pigeons fly in heavy smog during a polluted day in Beijing, China, December 19, 2016. (Photo by Reuters/Stringer)





A woman wearing a mask walks along a bridge in smog during a polluted day in Tianjin, China, December 19, 2016. (Photo by Reuters/Stringer)





A man wearing a mask is seen in smog during a polluted day in Harbin, Heilongjiang province, China, December 19, 2016. (Photo by Reuters/Stringer)





A woman sits on the back of a motorcycle in smog during a polluted day in Liaocheng, Shandong province, China, December 19, 2016. (Photo by Reuters/Stringer)





People walk across a road in smog during a polluted day in Tianjin, China, December 19, 2016. (Photo by Reuters/Stringer)





Assistants set up 24 mobile phones on artist Liu Bolin's vest before he live broadcasts air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





Artist Liu Bolin wearing a vest with 24 mobile phones stands in front of a poster promoting the core values of Chinese socialism as he live broadcasts air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





A woman is pictured behind artist Liu Bolin wearing a vest with 24 mobile phones as he walks along a street during a live broadcast of air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





Artist Liu Bolin wearing a vest with 24 mobile phones stands in the middle of a road during morning rush hour as he live broadcasts air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





Artist Liu Bolin wearing a vest with 24 mobile phones stands in smog as he live broadcasts air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





Artist Liu Bolin wearing a vest with 24 mobile phones walks in smog as he live broadcasts air pollution in the city on the fourth day after a red alert was issued for heavy air pollution in Beijing, China, December 19, 2016. (Photo by Jason Lee/Reuters)





A machine is used to reduce pollution at a construction side during a polluted day in Beijing, China, December 18, 2016. (Photo by Reuters/Stringer)





A machine is used to reduce pollution at a construction side during a polluted day in Beijing, China, December 18, 2016. (Photo by Reuters/Stringer)





A food vendor waits for customers as heavy smog blankets Shengfang, in Hebei province, on an extremely polluted day with red alert issued, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





Women wearing face masks wait for the bus on an extremely polluted day with red alert issued, in Langfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A couple wearing face masks walk past a tricycle taxi on an extremely polluted day with red alert issued, in Langfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





People ride a bus on an extremely polluted day with red alert issued, in Langfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





People wait for the bus on an extremely polluted day with red alert issued, in Langfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A woman wearing a face mask rides a moped on an extremely polluted day with red alert issued, in Langfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





People make their way through heavy smog on an extremely polluted day with red alert issued, in Shengfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A man cooks in open air as heavy smog blankets Shengfang, in Hebei province, on an extremely polluted day with red alert issued, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





People make their way through heavy smog on an extremely polluted day with red alert issued, in Shengfang, Hebei province, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A street food vendor waits for customers as heavy smog blankets Shengfang, in Hebei province, on an extremely polluted day with red alert issued, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





People wait for street food as heavy smog blankets Shengfang, in Hebei province, on an extremely polluted day with red alert issued, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A street food vendor prepares food for customers as heavy smog blankets Shengfang, in Hebei province, on an extremely polluted day with red alert issued, China December 19, 2016. (Photo by Damir Sagolj/Reuters)





A member of the security personnel wearing a mask stands guard in the smog at Tiananmen Square after a red alert was issued for heavy air pollution in Beijing, China, December 20, 2016. (Photo by Jason Lee/Reuters)





A man wearing a respiratory protection mask is pictured in the subway after a red alert was issued for heavy air pollution in Beijing, China, December 20, 2016. (Photo by Jason Lee/Reuters)





A paramilitary police officer wearing a mask stands guard in front of a portrait of the late Chairman Mao Zedong during smog at Tiananmen Square after a red alert was issued for heavy air pollution in Beijing, China, December 20, 2016. (Photo by Jason Lee/Reuters)





People wearing masks cycle past Tiananmen Gate during the smog after a red alert was issued for heavy air pollution in Beijing, China, December 20, 2016. (Photo by Jason Lee/Reuters)





Buildings are seen in heavy smog during a polluted day in Jinan, Shandong province, China, December 20, 2016. (Photo by Reuters/Stringer)





A citizen rides in smog on December 20, 2016 in Jinan, Shandong Province of China. Air quality index (AQI) readings exceeded 400 and some schools have suspended classes in Jinan. (Photo by VCG/VCG via Getty Images)





A man smokes as he rides in smog during polluted day in Beijing, China, December 20, 2016. (Photo by Reuters/Stringer)





This photo taken on December 19, 2016 shows face masks on stone monkey statues in protest of the current heavy air pollution at Beijing Zoo in Beijing. Heavy smog suffocated northeast China for a fifth day on December 20, with hundreds of flights cancelled and road and rail transport grinding to a halt under the low visibility conditions. (Photo by AFP Photo/Stringer)





A Chinese girl wears a mask at Jingshan Park during the haze day in Beijing, China, 19 December 2016. Serious air pollution hit in China's nine provinces and cities, with haze hanging over an area of about 1.42 million square kilometers on 18 December. The air pollution alert lasts in many part of China that the heavy pollution is expected to persist over 11 provinces and cities on 19 December 2016. (Photo by Wu Hong/EPA)





Chinese people wearing masks for protection against pollution walk at Ritan Park shrouded by heavy smog in Beijing, Monday, December 19, 2016. (Photo by Andy Wong/AP Photo)