Heavy fog covers a bridge spanning the Nile river in the Egyptian capital Cairo on December 23, 2019. (Photo by Mohamed el-Shahed/AFP Photo)





Mist over the town of Keswick in the Lake District, England after temperatures dipped to minus 2 degress Celsius on November 18, 2019. (Photo by Owen Humphreys/PA Images via Getty Images)





Sunrise in Inverleith Park, with a view of Edinburgh Castle in Edinburgh, England on December 25, 2019. (Photo by Craig Brown/Alamy Live News)





The sun begins to rise behind a mist covered Corfe Castle in Dorset, England on October 22, 2019. (Photo by Andrew Matthews/PA Images via Getty Images)





A general view of heavy fog and air pollution covering the Skopje valley in the early morning, in Skopje, North Macedonia, 16 December 2019. According to the World Health Organization (WHO), Skopje in 2018 became the most polluted capital city in Europe reaching alarmingly annual mean of high rates of fine particulate matter (PM2.5) air pollutants. (Photo by Georgi Licovski/EPA/EFE)





The light of the still low sun shines on the hills of the hoar-frost-covered Alpine foothills in Bernbeuren, Germany on December 30, 2019. (Photo by Karl-Josef Hildenbrand/dpa)





The Wallace Monument is shrouded in fog as it floats through the Carse of Stirling on Christmas morning in Scotland on December 25, 2019. (Photo by Andrew Milligan/PA Images via Getty Images)





Deer are seen grazing as cyclists ride past in the early morning mist in Richmond Park, west London, Britain, December 30, 2019. (Photo by Toby Melville/Reuters)





People ride a boat on the Tianquan Lake during a foggy day in Xuyi in China's eastern Jiangsu province on November 20, 2019. (Photo by AFP Photo/China Stringer Network)





Mist clears away on a sunny autumn day in the Valley de Joux near Le Chenit, Switzerland, October 23, 2019. (Photo by Denis Balibouse/Reuters)





A man walks along a canal amid golden, green and rusty leaves in Thun-Leveque, France on November 19, 2019. (Photo by Pascal Rossignol/Reuters)





Steam caused by pipe damage rises over Powsinska street in Warsaw, Poland on December 10, 2019. (Photo by Pawel Guraj/Reuters)





The sun emerges on a foggy day after snowfall in Almaty, Kazakhstan on December 16, 2019. (Photo by Pavel Mikheyev/Reuters)





Fog covers the AP-9 bridge in Cabanas, Galicia, northwestern Spain, 22 October 2019. Warnings for heavy rain have been issued in various regions in the Spanish territory. (Photo by EPA/Cabalar)





A migrant carries water to the Vucjak refugee camp outside Bihac, northwestern Bosnia, Sunday, December 8, 2019. It has been reported that Bosnian officials will close the makeshift tent camp in northwestern Bosnia where hundreds of migrants remain stranded despite snow and freezing weather. (Photo by Kemal Softic/AP Photo)





In this picture taken with a drone fog covers the ground on Szentendre Island near Pocsmegyer, northern Hungary, 19 October 2019. (Photo by Balazs Mohai/EPA/EFE/Rex Features/Shutterstock)





Early risers were greeted by fog on Brading Down, Isle of Wight off the south coast of England on December 31, 2019. Today will be damp in the southwest but largely dry and mild elsewhere. (Photo by Sienna Anderson/Soul Photography)





A general view of the sea of fog covering the Mount of San Cristobal in Pamplona, northern Spain, 25 December 2019. (Photo by Jesus Diges/EPA/EFE/Rex Features/Shutterstock)