Smog had become a frequent part of London life, but nothing quite compared to the smoke-laden fog that shrouded the capital from Friday 5 December to Tuesday 9 December 1952.
Early on 5 December in the London area, the sky was clear, winds were light and the air near the ground was moist.
Accordingly, conditions were ideal for the formation of radiation fog.
The sky was clear, so a net loss of long-wave radiation occurred and the ground cooled. The moist air in contact with the ground cooled to its dew-point temperature and condensation occurred.
Cool air drained katabatically into the Thames Valley. Beneath the inversion of the anticyclone, the very light wind stirred the saturated air upwards to form a layer of fog 100–200 metres deep. Along with the water droplets of the fog, the atmosphere beneath the inversion contained the smoke from innumerable chimneys in the London area and farther afield. Elevated spots such as Hampstead Heath were above the fog and grime. From there, the hills of Surrey and Kent could be seen.
During the day on 5 December, the fog was not especially dense and generally possessed a dry, smoky character. When nightfall came, however, the fog thickened. Visibility dropped to a few metres. The following day, the sun was too low in the sky to make much of an impression on the fog. That night and on the Sunday and Monday nights, the fog again thickened. In many parts of London, it was impossible at night for pedestrians to find their way, even in familiar districts. In the Isle of Dogs, the visibility was at times nil. The fog there was so thick that people could not see their own feet! Even in the drier thoroughfares of central London, the fog was exceptionally thick. Not until 9 December did it clear. In central London, the visibility remained below 500 metres continuously for 114 hours and below 50 metres continuously for 48 hours. At Heathrow Airport, visibility remained below ten metres for almost 48 hours from the morning of 6 December.
Huge quantities of impurities were released into the atmosphere during the period in question. On each day during the foggy period, the following amounts of pollutants were emitted: 1,000 tonnes of smoke particles, 2,000 tonnes of carbon dioxide, 140 tonnes of hydrochloric acid and 14 tonnes of fluorine compounds. In addition, and perhaps most dangerously, 370 tonnes of sulphur dioxide were converted into 800 tonnes of sulphuric acid. At London's County Hall, the concentration of smoke in the air increased from 0.49 milligrams per cubic metre on 4 December to 4.46 on the 7th and 8th.
The infamous fog of December 1952 has come to be known as 'The Great Smog'; the term 'smog' being a portmanteau word meaning 'fog intensified by smoke'. The term was coined almost half a century earlier, by HA Des Voeux, who first used it in 1905 to describe the conditions of fuliginous (sooty) fog that occurred all too often over British urban areas. It was popularised in 1911 when Des Voeux presented to the Manchester Conference of the Smoke Abatement League of Great Britain a report on the deaths that occurred in Glasgow and Edinburgh in the Autumn of 1909 as a consequence of smoke-laden fogs.
Legislation followed the Great Smog of 1952 in the form of the City of London (Various Powers) Act of 1954 and the Clean Air Acts of 1956 and 1968. These Acts banned emissions of black smoke and decreed that residents of urban areas and operators of factories must convert to smokeless fuels. As these residents and operators were necessarily given time to convert, however, fogs continued to be smoky for some time after the Act of 1956 was passed. In 1962, for example, 750 Londoners died as a result of a fog, but nothing on the scale of the 1952 Great Smog has ever occurred again.
Note
An anticyclone (that is, opposite to a cyclone) is a weather phenomenon defined by the United States' National Weather Service's glossary as "large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere".Effects of surface-based anticyclones include clearing skies as well as cooler, drier air. Fog can also form overnight within a region of higher pressure. Mid-tropospheric systems, such as the subtropical ridge, deflect tropical cyclones around their periphery and cause a temperature inversion inhibiting free convection near their center, building up surface-based haze under their base. Anticyclones aloft can form within warm core lows, such as tropical cyclones, due to descending cool air from the backside of upper troughs, such as polar highs, or from large scale sinking, such as the subtropical ridge.
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a "temperature inversion", i.e., an increase in temperature with height, or to the layer ("inversion layer") within which such an increase occurs.
An inversion can lead to pollution such as smog being trapped close to the ground, with possible adverse effects on health. An inversion can also suppress convection by acting as a "cap". If this cap is broken for any of several reasons, convection of any moisture present can then erupt into violent thunderstorms. Temperature inversion can notoriously result in freezing rain in cold climates.
For further study:
http://www.martinfrost.ws/htmlfiles/great_smog.html
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