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)

A United Launch Alliance Delta IV heavy rocket carrying classified spy satellite cargo for the U.S. National Reconnaissance Office lifts off from Space Launch Complex 37B at the Cape Canaveral Space Force Station, Tuesday, April 9, 2024, in Cape Canaveral, Fla. This is the final flight of a Delta IV heavy rocket. (Photo by John Raoux/AP Photo)

A citizen rides in smog on December 20, 2016 in Jinan, Shandong Province of China. Air quality index (AQI) readings exceeded 400 and some schools have suspended classes in Jinan. (Photo by VCG/VCG via Getty Images)

A vendor sells beef at a market in Hanoi, Vietnam 01 October 2024. Vietnam's official manufacturing Purchasing Managers' Index (PMI) declined to 47.3 points in September, down from 52.4 points in the previous month, according to the latest survey from S&P Global. (Photo by Luong Thai Linh/EPA)

A Mark IV tank, part of the parade at the Lord Mayor's Show in London. (Photo by Topical Press Agency/Getty Images). November 1917

October winner. “A burst of the aurora borealis over Kirkjufell, taken in September 2016. This shot has been a holy grail for me and was finally captured after many trips”. MICK RYAN, JUDGE: Iceland is a hotspot for aurora photography and this composition of the symmetric, free-standing Kirkjufell and the trident waterfall is much-sought after. If you can time your visit when the aurora “kp” index is high and know the settings for nighttime aurora images, you may end up with a beautiful photograph like this. (Photo by DВ/The Guardian)

An American soldier walks ahead of an MKIV (Mark IV) British-made tank, circa 1918. (Photo by Hulton Archive/Getty Images)

World medieval jousting champion Rod Walker poses before next month’s St Ives Medieval Faire, the only solid wood lance joust tournament in the southern hemisphere in Sydney, Australia on August 26, 2016. (Photo by Dan Himbrechts/AAP)