http://en.wikipedia.org/wiki/Great_Smog :
The Great Smog of '52 or Big Smoke[1] was a severe air pollution event that affected London during December 1952. A period of cold weather, combined with an anticyclone and windless conditions, collected airborne pollutants mostly from the use of coal to form a thick layer of smog over the city. It lasted from Friday 5 to Tuesday 9 December 1952, and then dispersed quickly after a change of weather.
Although it caused major disruption due to the effect on visibility, and even penetrated indoor areas, it was not thought to be a significant event at the time, with London having experienced many smog events in the past, so called "pea soupers". However, government medical reports in the following weeks estimated that up until 8th December 4,000 people had died prematurely and 100,000 more were made ill because of the smog's effects on the human respiratory tract. More recent research suggests that the total number of fatalities was considerably greater at about 12,000.[2]
It is known to be the worst air pollution event in the history of the United Kingdom,[3] and the most significant in terms of its effect on environmental research, government regulation, and public awareness of the relationship between air quality and health.[2] It led to several changes in practices and regulations, including the Clean Air Act 1956.
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[edit] Events
[edit] Sources of pollution
The weather preceding and during the smog meant that Londoners were burning more coal than usual to keep warm. Post-war domestic coal tended to be of a relatively low-grade, sulphurous variety (economic necessity meant that better-quality "hard" coals tended to be exported), which increased the amount of sulphur dioxide in the smoke. There were also numerous coal-fired power stations in the Greater London area, including Battersea, Bankside, and Kingston upon Thames, all of which added to the pollution. Research suggests that additional pollution prevention systems fitted at Battersea may have actually worsened the air quality, reducing the output of soot at the cost of increased sulphur dioxide, though this is not certain. Additionally, there were pollution and smoke from vehicle exhaust—particularly from diesel-fuelled buses which had replaced the recently abandoned electric tram system—and from other industrial and commercial sources.[4] Prevailing winds had also blown heavily polluted air across the English Channel from industrial areas of Continental Europe.
[edit] Weather
On 4 December 1952, an anticyclone settled over a windless London, causing a temperature inversion with cold, stagnant air trapped under a layer (or "lid") of warm air.[5][6] The resultant fog, mixed with chimney smoke, particulates such as those from 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 yellow-black colour, hence the nickname "peasouper".[4] The absence of significant wind prevented its dispersal and allowed an unprecedented accumulation of pollutants. When the smog eventually cleared away there was a black-grey covering of slimy soot particles on all of the top surfaces out of doors. This sooty grime stayed there until a few days later when the first rains came. This soot covering was then washed off the surface of evergreen leaves, buildings and pavements, etc., into gutters and down the drains in dirty black rivulets. The pungent smell about in the atmosphere was of acrid wet soot, which made the eyes and nostrils smart for those unfortunate to be caught out in the open.
[edit] Effect on London
Although London was accustomed to heavy fogs, this one was denser and longer-lasting than any previous fog.[7] Visibility was reduced to a few yards ("It's like you were blind", commented one observer),[8] making driving difficult or impossible.
Public transport ceased, apart from the London Underground; and the ambulance service stopped functioning, forcing sick people to transport themselves to hospital.[8] The smog even seeped indoors, resulting in the cancellation or abandonment of concerts and film screenings as visibility decreased in large enclosed spaces, and stages and screens became harder to see from the seats. Outdoor sports events were also affected.
In the inner London suburbs and away from town centres there was no disturbance by moving traffic to thin out the dense fog in the back streets. The result was that visibility could be down to a metre or so in the daytime. Walking out of doors became a matter of shuffling one’s feet to feel for road kerbs, etc. This was made even worse at night because each back street lamp at the time was fitted with an incandescent light-bulb which gave no penetrating light onto the pavement for pedestrians to see their feet, or even the lamp post. Fog-penetrating fluorescent lamps did not become widely available until later on in the Fifties. ‘Smog masks’ were worn by those who were able to purchase them from chemists.
Near railway lines, on which 'fog working' was implemented, loud explosions similar to the report of a shotgun were a common feature. These explosions were made by 'detonators', a form of large percussion cap placed on the track and activated by the wheels of trains. These were placed by certain signals to provide an audible warning to match the visual indication provided by the signal for the driver.
[edit] Health effects
There was no panic, as London was renowned for its fog. In the weeks that ensued, however, statistics compiled by medical services found that the fog had killed 4,000 people.[9] Most of the victims were very young or elderly, or had pre-existing respiratory problems. In February 1953, Lieutenant-Colonel Lipton suggested in the House of Commons that the fog had caused 6,000 deaths and that 25,000 more people had claimed sickness benefits in London during that period.[10]
Most of the deaths were caused by respiratory tract infections from hypoxia and as a result of mechanical obstruction of the air passages by pus arising from lung infections caused by the smog. The lung infections were mainly bronchopneumonia or acute purulent bronchitis superimposed upon chronic bronchitis.[11]
More recent research suggests that the number of fatalities was considerably greater, at about 12,000.[2]
[edit] Environmental impact
The death toll formed an important impetus to modern environmentalism, and it caused a rethinking of air pollution, as the smog had demonstrated its lethal potential.
New regulations were implemented, restricting the use of dirty fuels in industry and banning black smoke.
Environmental legislation since 1952, such as the City of London (Various Powers) Act 1954 and the Clean Air Acts of 1956 and 1968, led to a reduction in air pollution. Financial incentives were offered to householders to replace open coal fires with alternatives, (such as installing gas fires) or for those who preferred, to burn coke instead (a bi-product of town gas production) which produces minimal smoke. Central heating (using gas, electricity, oil or permitted solid fuel) was rare in most dwellings at that time, not finding favour until the late 1960s onwards.
Despite improvements, insufficient progress had been made to prevent one further smog event exactly ten years later in early December 1962.
