December 5 - 1952 - The Great Smog of London
When Londoners woke up on December 5 in 1952, they found the entire city covered in a mass of smog. London had been battling pollution from coal burning since the 13th century, and large smog events had taken place elsewhere in the world in the preceding two centuries. Yet the Great Smog of London, as it would become known, was something truly different. It occurred because of an anticyclone, a spinning of air that actually creates a layer of still, unmoving air and a dense fog. When that fog mixed with the ever present pollution in London, a special kind of "pea soup fog," so called for its resemblance to the foodstuff, had overwhelmed the entire city. Visibility was reduced to just a few metres, and very few events took place outside. Trains could only run with the help of loud auditory aids. At the time, hospitals recorded 4,000 deaths, but that was low because ambulances were not running. Most likely, something like 12,000 people passed away from breathing problems and visibility related deaths. In 1956, Parliament passed the Clean Air Act, which helped to ensure that no further great smogs could take place.