On December 5, 1952, The Great Smog of ’52 or Big Smoke – a severe air pollution event began and affected London, UK for six days. Cold weather conditions combined with an anticyclone and lack of wind, collected airborne pollutants mostly from the use of coal to form a thick layer of smog over the city. Though not considered to be a significant event at the time, medical reports in the following weeks estimated that 4,000 people had died prematurely and 100,000 more were made ill because of the smog’s effects on the human respiratory tract. More recent research indicates that the number of fatalities was closer to about 12,000.
The Great Smog is considered the worst air pollution event in the history of the United Kingdom, and the most significant in terms of its effect on environmental research, government regulation, and public awareness of the relationship between air quality and health. It led to several changes in practices and regulations, including the Clean Air Act 1956. (wiki)