A woman wearing a mask walk in a street in a Yonghegong Lama temple compound seen shrouded in smog in Beijing, China, 30 November 2015. Beijing issued an orange alert for heavy smog 30 November, the highest level this year. Authorities in the Chinese capital warned of 'severe pollution' and advised the capital's 20 million inhabitants to stay indoors. (Photo by How Hwee Young/EPA)

Andrew Hepher, Vice President of Lubricants Technology, Shell unveils the Shell Concept Car in Beijing, China, Friday, April 22, 2016. Built as proof of energy efficiency that can be achieved with the latest technologies, Shell unveiled the concept car ahead of the bi-annual Beijing Auto Show where the world's top car manufacturers will showcase their own upcoming products. (Photo by Ng Han Guan/AP Photo)

A performer takes part in the opening of the Temple Fair, part of Chinese New Year celebrations at Ditan Park, also known as the Temple of Earth, in Beijing, February 18, 2015. (Photo by Kim Kyung-Hoon/Reuters)

A Chinese man uses an old film camera to take a picture of relatives near the Forbidden City on March 27, 2014 in Beijing, China. (Photo by Kevin Frayer/Getty Images)

Graduates jump as they pose for photographs in front of the Tiananmen Gate and the giant portrait of late Chinese Chairman Mao Zedong, on the Tiananmen Square in Beijing, June 19, 2014. (Photo by Reuters/Stringer)

A woman lies to pose for her souvenir picture on the glass sightseeing platform on Shilin Gorge in Beijing, China, May 27, 2016. (Photo by Kim Kyung-Hoon/Reuters)

A woman dressed in a Tang-dynasty costume performs at a show by designer Chu Yan at China Fashion Week in Beijing, China, October 30, 2018. (Photo by Jason Lee/Reuters)

In this Sunday, March 5, 2017 photo, hospitality staff pose for photos on Tiananmen Square during the National People's Congress held at the Great Hall of the People in Beijing. (Photo by Andy Wong/AP Photo)