Great Smog of London

Battersea Power Station in 1938

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,[10] post-war domestic coal tended to be of a relatively low-grade, sulphurous variety (similar to lignite) which increased the amount of sulphur dioxide in the smoke. There were also numerous coal-fired power stations in the Greater London area, including Fulham, Battersea, Bankside, Greenwich 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.[5] The relatively large size of the water droplets in London fog allowed the production of sulphates without the acidity of the liquid rising high enough to stop the reaction, and the resultant weak acid become concentrated when the fog was burned away by the sun.[11]

Research suggests that additional pollution-prevention systems fitted at Battersea may have worsened the air quality. Flue-gas washing reduced the temperature of the flue-gases; so they did not rise but instead slumped to a ground level, causing a local nuisance.[12]

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.[13]

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.[14][15] 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 yellow-black colour, hence the nickname "pea-souper".[13] The absence of significant wind prevented its dispersal and allowed an unprecedented accumulation of pollutants.

Although London was accustomed to heavy fogs, this one was denser and longer-lasting than any previous fog.[16] Visibility was reduced to a few metres ("It's like you were blind"[17]) making driving difficult or impossible.

Public transport ceased, apart from the London Underground, and the ambulance service stopped, forcing users to transport themselves to the hospital. The smog was so dense that it even seeped indoors, resulting in 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.[18] Outdoor sports events were also cancelled.[19]

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. As a result, 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 potential obstacles such as road kerbs. This was made even worse at night since 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 in the 1950s. "Smog masks" were worn by those who were able to purchase them from chemists.

There was no panic, as London was infamous for its fog. In the weeks that ensued, however, statistics compiled by medical services found that the fog had killed 4,000 people.[20] Most of the victims were very young or elderly, or had pre-existing respiratory problems. In February 1953, Marcus 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.[21]

Mortality remained elevated for months after the fog. A preliminary report, never finalised, blamed those deaths on an influenza epidemic.[1] Emerging evidence revealed that only a fraction of the deaths could be from influenza.[22] 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.[23][24][25] The lung infections were mainly bronchopneumonia or acute purulent bronchitis superimposed upon chronic bronchitis.[26][27]

Research published in 2004 suggests that the number of fatalities was considerably greater than contemporary estimates, at about 12,000.[1][2]

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 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 approximately ten years later, in early December 1962.[28]