A couple walk in the Retiro park in Madrid on November 17, 2020 as a thick fog falls on the Spanish capital. (Photo by Gabriel Bouys/AFP Photo)

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)

Students are seen on a pickup truck at the agricultural road which leads to the capital city of Cairo, Egypt, October 13, 2016. (Photo by Amr Abdallah Dalsh/Reuters)

Men hang at the back of a truck loaded with farm produce along a road in Ikeja district in the commercial capital Lagos, Nigeria December 19, 2016. (Photo by Akintunde Akinleye/Reuters)

Dancers perform during the carnival in Encarnacion, Paraguay on February 26, 2017. Encarnacion is located 375 km south of Asuncion, describes itself as the “Carnival Capital of Paraguay”. (Photo by Norberto Duarte/AFP Photo)

A woman plays billiards during a local championship at a sports hall in Yemen's capital Sanaa on December 16, 2019. (Photo by Mohammed Huwais/AFP Photo)

Girls in floral crowns jump across the bonfire while holding hands during the Kupala Night celebration at the National Museum of Folk Architecture and Life in Pyrohiv, Kyiv, capital of Ukraine. (Photo by Ukrinform/Rex Features/Shutterstock)

A demonstrator takes part during a rally against Chile's government on the second anniversary of the protests and riots that rocked the capital in 2019, in Santiago, Chile, October 18, 2021. (Photo by Ivan Alvarado/Reuters)