6 December 2012 Last updated at 06:05 ET

Valued exposure: London smog

Heavy smog in Piccadilly Circus, London, 6 December 1952

Sixty years ago thick smog descended on London, contributing to the deaths of an estimated 4,000 people. The four-day "pea-souper", while worse than usual, was a familiar experience for Londoners. The legacy of the Great Smog was the Clean Air Act of 1956 which introduced a number of measures to reduce pollution. Photo by Central Press/Hulton Archive/Getty Images.

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