Most lethal smog

On 5–9 December 1952, London was blanketed by thick smog, caused by cold weather, coupled with an anticyclone that allowed the build-up of pollutants. The total number of fatalities was as high as 12,000 and this led to the creation of the Clean Air Act in 1956. In November 2016, an international team of scientists published their analysis of the disaster, in which sulphur dioxide and nitrogen dioxide from residential and power plant coal burning formed sulphuric acid when mixed with natural fog particles. The 2016 study showed similarities between the chemistry in the "Great Smog of 1952" and current urban air pollution in China.