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)

A man gets ready backstage before performing in the 35th Cochin Carnival, which is held annually to welcome the start of the New Year at Fort Kochi in the southern state of Kerala, India, January 1, 2019. (Photo by Sivaram V/Reuters)

A model on the catwalk for the Tom Ford show at New York fashion week in New York, USA on September 6, 2017. (Photo by Swan Gallet/Shutterstock)

Rohingya refugee sisters Nur Kaida (R) and Ruhana hug each other at their shelter at the Palongkhali refugee camp near Cox's Bazar, Bangladesh December 21, 2017. (Photo by Marko Djurica/Reuters)

Vehicles pass through the heavy fog and air pollution that cover Skopje valley in the early morning, in Skopje, The Former Yugoslav Republic of Macedonia, 14 December 2017. According to media reports, Skopje is considered one of the most polluted cities in the world. (Photo by Georgi Licovski/EPA/EFE)

Chinese model Ming Xi falls down on runway during the 2017 Victoria's Secret Fashion Show at Mercedes-Benz Arena on November 20, 2017 in Shanghai, China. (Photo by VCG/VCG via Getty Images)

Jessie Jo Stark and Bella Hadid attend Chrome Hearts X Bella Hadid Collaboration Launch as part of Paris Fashion Week at Chrome Hearts on March 4, 2017 in Paris, France. (Photo by Julien M. Hekimian/Getty Images for Chrome Hearts)

Bicycles of various bike-sharing services are seen at an urban village in smog during a polluted day in Shanghai, 2017. Rapid expansion of shared bicycle companies across China has led to massive piles of abandoned bikes as supply outstrips demand. (Photo by Aly Song/Reuters)