A Boeing 777-300 from Swiss International Airlines lands on a foggy morning at Zurich Airport, on Friday, October 13, 2017, in Zurich, Switzerland. The high humidity renders the air vortex visible. (Photo by Christian Merz/Keystone via AP Photo)

A Viet Cong suspect holds his hands up after a Vietnamese Ranger from the 21st Vietnam Infantry Division routed him from his hiding place. (Photo by Keystone/Getty Images). 7th November 1967

Andre Krumbiegel drives in a «SIL» pointed plough through the pink fog of a smoke body in Saxony, Germany on October 2, 2019. The occasion is the forthcoming Eastern Bloc meeting on 6 October in Großhartmannsdorf, to which motor vehicles and commercial vehicles from former socialist countries can be brought, exhibited and demonstrated. Photo by Sebastian Kahnert/dpa-Zentralbild/Keystone)

The Swiss Air Force Patrouille Suisse aerobatic team performs during the men's downhill race at the Alpine Skiing FIS Ski World Cup in Wengen, Switzerland, Saturday, January 19, 2019. (Photo by Anthony Anex/Keystone via AP Photo)

In this February 4, 2016 picture a masked participant of the traditional carnival parade poses in the streets of the village of Kippel in the Loetschental valley, southwestern part of Switzerland. During this sinister carnival, participants wearing wooden masks and animal furs, crowd the streets of the villages to scare the people. (Photo by Dominic Steinmann/Keystone via AP Photo)

Young people fight for fun with their pillows, during the International Pillow Fight Day at the Place des Grottes, in Geneva, Switzerland, Saturday, April 4, 2015. The annual International Pillow Fight Day takes place in hundreds of cities around the world. (Photo by Salvatore Di Nolfi/AP Photo/Keystone)

Battle-weary American troops withdraw from Yong San in Korea. (Photo by Keystone/Getty Images). 1950

Children in Hiroshima, Japan, wearing masks to combat the odour of death after the city was destroyed by the first atom bomb. (Photo by Keystone/Getty Images). 1945