4.The Great Smog of London
In winter of 1952, an exceptionally cold and thick fog settled over London, encouraging London population to burn larger amount of coal for heating. In just two days, the thick fog was clogged by fine coal particles and soot, making it dangerous to drive on the road. All outdoor entertainment and public events were cancelled; staying indoor didn’t help either. Within a few months, about 12,000 deaths associated with respiratory problems were recorded and it was estimated that 100,000 people suffered health problems in varying degree. The deadly smog lasted for four days and finally dispersed when wind finally returned. The event led to the 1956 Clean Air Act.