People walk under Australia's iconic landmark Harbour Bridge in Sydney on April 3, 2019, as heavy fog blankets the city. Low visibility due to heavy fog affected traffic in the city and caused flight delays at the Sydney airport. (Photo by Saeed Khan/AFP Photo)

Jaime “Ka Diego” Padilla (R), spokesperson of the Melito Glor Command of the New People's Army (NPA), and Ka Kathryn (Comrade Kathryn) (L) react during their 50th founding anniversary celebration at an undisclosed location in the mountains of Sierra Madre, Philippines, 31 March 2019. (Photo by Alecs Ongcal/EPA/EFE)

Participants dance during the Water Gun Festival on July 07, 2019 in Seoul, South Korea. Thousands of people enjoyed the annual festival which is being held over the weekend during the scorching heat summer in Korea. (Photo by Chung Sung-Jun/Getty Images)

Competitors Taisto Miettinen and Katja Kovanen fron Finland participate in the annual Wife Carrying World Championships in Sonkajarvi, Finland on July 6, 2019. People from all over the world took part in the event that was founded in 1992. (Photo by Mauri Ratilaine/EPA/EFE/Rex Features/Shutterstock)

People celebrate after Gov. Ricardo Rossello announced that he is resigning Aug. 2 after weeks of protests over leaked obscene, misogynistic online chats, in San Juan, Puerto Rico, Thursday, July 25, 2019. (Photo by Carlos Giusti/AP Photo)

Participants in fancy costumes take part in march during the Prague Pride parade in downtown Prague, Czech Republic, 10 August 2019. Several thousands of people attended the 9th Prague Pride to support the LGBT (lesbian, gay, bisexual and transgender) communities. (Photo by Martin Divisek/EPA/EFE/Rex Features/Shutterstock)

A “colacho” (a person dressed up as a devil) chases people during “El salto del Colacho”, the baby jumping festival in the village of Castrillo de Murcia, near Burgos on June 3, 2018. (Photo by Cesar Manso/AFP Photo)

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)