A vendor arranges a shelf full of masks as he waits for customers in a shopping mall in Yiwu, Zhejiang province, China, December 7, 2015. Picture taken December 7, 2015. (Photo by Reuters/China Daily)





A women wearing a mask to protect from extreme smog visits the Tiananmen Gate in Beijing December 8, 2015 as China's capital issues its first ever "red alert" for pollution. (Photo by Damir Sagolj/Reuters)





In this December 8, 2015 photo, a woman wears a mask to protect herself from pollutants on a heavily polluted day in Beijing. Episodes of nauseating smog lasting several days has become part of wintertime in Beijing. (Photo by Andy Wong/AP Photo)





In this December 8, 2015 photo, a woman wears a mask to protect herself from pollutants near the Forbidden City on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 8, 2015 photo, a woman wears a mask to protect herself from pollutants on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 8, 2015 photo, a woman wears a mask to protect herself from pollutants near the Forbidden City on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 8, 2015 photo, a man wears a mask to protect himself from pollutants on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 8, 2015 photo, a woman wears a mask to protect herself from pollutants near the Forbidden City on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a man wears a mask to protect himself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





A boy wearing a mask sits on the shoulders of a man as they watch a flag-raising ceremony amid heavy smog at the Tiananmen Square, after the city issued its first ever "red alert" for air pollution, in Beijing, China, December 8, 2015. (Photo by Reuters/Stringer)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a man wears a mask to protect himself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





A child wears a protective mask to shield from extreme smog in central Beijing December 8, 2015 as China's capital issues its first ever "red alert" for pollution. (Photo by Damir Sagolj/Reuters)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a couple wears matching panda themed masks to protect themselves from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





A vendor wears mask to sell national flag and selfie stick at Tiananmen Square during a haze day in Beijing city, China, 08 December 2015. Beijing has issued its first red alert for air pollution under a four-tier emergency response system created in October 2013. The red alert which is the most serious level for Air Quality Index (AQI), last from 7 a.m. on 08 December to 12 a.m. on 10 December. (Photo by Wu Hong/EPA)





In this December 1, 2015 photo, a woman wears a mask to protect herself from pollutants near Tiananmen Gate on a heavily polluted day in Beijing. (Photo by Andy Wong/AP Photo)





Morning commuters wait in line at the Tiantongyuan subway station on a smoggy day after the city issued its first ever "red alert" for air pollution, in Beijing, China, December 8, 2015. (Photo by Reuters/China Daily)