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Great Smog of London

1952 air pollution event

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The smog caused major disruption by reducing visibility and even penetrating indoor areas, far more severely than previous smog events, called "pea-soupers". Government medical reports in the weeks following the event estimated that up to 4,000 people had died as a direct result of the smog and 100,000 more were made ill by the smog's effects on the human respiratory tract. More recent research suggests that the total number of fatalities was considerably greater, with estimates of between 10,000 and 12,000 deaths.

London's poor air quality had been a problem since at least the 13th century. The diarist John Evelyn had written about "the inconveniencie of the aer and smoak of London [sic]" in Fumifugium, the first book written about air pollution, in 1661. However, the Great Smog was many times worse than anything the city had ever experienced before: it is thought to be the worst air pollution event in the history of the United Kingdom, and the most significant for its effects 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.

Background

Sources of pollution

A period of unusually cold weather preceding and during the Great Smog led Londoners to burn much more coal than usual to keep themselves warm. While better-quality "hard" coals (such as anthracite) tended to be exported to pay off World War II debts, post-war domestic coal tended to be of a relatively low-grade, sulphurous variety called "nutty slack" (similar to lignite) which increased the amount of sulphur dioxide in the smoke. There were also numerous coal-fired electric power stations in the Greater London area, including Fulham, Battersea, Bankside, Greenwich, West Ham and Kingston upon Thames, all of which added to the pollution. According to the UK's Met Office, the following pollutants were emitted each day during the smoggy period: 1,000 tonnes of smoke particles, 140 tonnes of hydrochloric acid, 14 tonnes of fluorine compounds and 370 tonnes of sulphur dioxide which may have been converted to 800 tonnes of sulphuric acid. The relatively large size of the water droplets in the London fog allowed for the production of sulphates without the acidity of the liquid rising high enough to stop the reaction, and for the resultant dilute acid to become concentrated when the fog was burned away by the sun.

Research suggested that additional pollution-prevention systems fitted at Battersea worsened the air quality. Flue gas washing reduced the temperature of the flue gases so they did not rise, but instead slumped to ground level, causing a local nuisance.

Additionally, there was pollution and smoke from vehicle exhaust, particularly from steam locomotives and diesel-fuelled buses which had replaced the recently abandoned electric tram system. Other industrial and commercial sources also contributed to the air pollution.

Weather

On 4 December 1952, an anticyclone settled over a windless London, causing a temperature inversion with relatively cool, stagnant air trapped under a layer of warmer air. The resultant fog, mixed with smoke from home and industrial chimneys, particulates such as those from motor vehicle exhausts, and other pollutants such as sulphur dioxide, formed a persistent smog, which blanketed the capital the following day. The presence of tarry particles of soot gave the smog its greenish-yellow colour, hence the nickname "pea-souper". The absence of significant wind prevented its dispersal and allowed an unprecedented accumulation of pollutants.

Although the event is now widely described as the "London" smog, air pollution, in fact, extended far beyond the capital. According to E. T. Wilkins (of the Department of Scientific and Industrial Research, whose measurements would make clear the connection between smoke, sulphur dioxide, and rising deaths), fog, white mist, or grimy smog covered "many parts of the British Isles", while "In London and the Thames Valley, fog or smog covered upwards of 1000 square miles". However, it was in London that the smog's effects were the greatest.

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