People in Kathmandu joke that the face mask has now become part of the national dress – an indispensable accessory in an effort to protect themselves from the dust. Nepal has the worst air quality in the world, according to the Environmental Performance Index. (Photo by Pete Pattisson/The Guardian)

Hollydell Poseidon ridden by Madeline Reader-Smith takes part in the Shetland Pony Grand National Flat Race in Aid of Bob Champion Cancer Trust during day two of the Cambridgeshire Meeting at Newmarket Racecourse on Friday, September 28, 2018. (Photo by Mike Egerton/PA Wire)

The US' winner Mikaela Shiffrin celebrates during a flowers ceremony after the women's Super G event of the 2019 FIS Alpine Ski World Championships at the National Arena in Are, Sweden, on February 5, 2019. (Photo by Denis Balibouse/Reuters)

A journalist uses their phone to take a picture at the press preview for “Vogue 100: A Century of Style” exhibiting the photographs that has been commissioned by British Vogue since it was founded in 1916 at National Portrait Gallery on February 10, 2016 in London, England. (Photo by Stuart C. Wilson/Getty Images)

A Chinese bus ushers jump as she pose for a photograph on Tiananmen Square during a plenary session of the National People's Congress held at the Great Hall of the People in Beijing, Wednesday, March 9, 2016. (Photo by Andy Wong/AP Photo)

Kenya Wildlife Service and Save The Elephants staff push an elephant as they undertake the collaring of ten elephants ranging near the Standard Gauge Railway to fit them with advanced satellite radio tracking collars in Tsavo National Park, Kenya March 15, 2016. (Photo by Goran Tomasevic/Reuters)

Gymnast Simone Biles performs a flip after throwing out the ceremonial first pitch prior to Game Two of the 2019 World Series between the Houston Astros and the Washington Nationals at Minute Maid Park on October 23, 2019 in Houston, Texas. (Photo by Tim Warner/Getty Images)

A combination of pictures shows people taking photos of themselves in Tiananmen Square as they celebrate National Day marking the 67th anniversary of the founding of the People's Republic of China, in Beijing October 1, 2016. (Photo by Damir Sagolj/Reuters)