The Great Smog of London, or Great Smog of 1952, was a severe air-pollution event that affected the British capital of London in early December 1952. A period of cold weather, combined with an anticyclone and windless conditions, collected airborne pollutants—mostly arising from the use of coal—to form a thick layer of smog over the city. It lasted from Friday, 5 December to Tuesday, 9 December 1952 and then dispersed quickly when the weather changed.
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Wikipedia
TIL that in 1952, 4,000 people were killed during a five-day smog in London
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The original link was: https://en.wikipedia.org/wiki/Great_Smog_of_1952