The Great Smog of London, or Great Smog of 1952, was a severe air-pollution event that affected the British capital of London in early December 1952.

A period of cold weather, combined with an anticyclone and windless conditions, collected airborne pollutants—mostly arising from the use of coal—to form a thick layer of smog over the city. The Great Smog of London lasted from Friday 5 December to Tuesday 9 December 1952 and then dispersed quickly when the weather changed.

It caused major disruption by reducing visibility and even penetrating indoor areas, far more severely than previous smog events experienced in the past, called “pea-soupers“.

Government medical reports in the following weeks, however, estimated that up until 8 December, 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 may have been considerably greater, one paper suggesting about 6,000 more died in the following months as a result of the event.

London had suffered since the 13th century from poor air quality, which worsened in the 1600s, but the Great Smog of London is known to be the worst air-pollution event in the history of the United Kingdom, 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. It led to several changes in practices and regulations, including the Clean Air Act 1956.

Sources of pollution

The cold weather preceding and during the Great Smog of London led Londoners to burn more coal than usual to keep themselves warm.

Post-war domestic coal tended to be of a relatively low-grade, sulfurous variety (similar to lignite coal), while conversely, better-quality “hard” coals (such as anthracite coal) tended to be exported to pay off World War II debts, which increased the amount of sulfur 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 the 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 sulfur dioxide which may have been converted to 800 tonnes of sulfuric acid.

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.

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 – and from other industrial and commercial sources.

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.

The resultant fog, mixed with smoke from home and industrial chimneys, particulates such as those from motor vehicle exhausts, and other pollutants such as sulfur 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 color hence the nickname “pea-souper“. The absence of significant wind prevented its dispersal and allowed an unprecedented accumulation of pollutants.

Effect on London

Although London was accustomed to heavy fogs, this one was denser and longer-lasting than any previous fog. Visibility was reduced to a few meters (“It’s like you were blind”) 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. Outdoor sports events were also canceled.

In the inner London suburbs and away from town centers, 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 meter 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 curbs.

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.

Near railway lines, on which “fog working” was implemented, loud explosions similar to a shotgun shot were common. The explosions were made by “detonators” – a form of large percussion cap placed on the track and activated by the wheels of trains.

These devices were placed by certain signals to provide an audible warning to match the visual indication provided by the signal for the driver.

Health effects

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.

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.

Mortality remained elevated for months after the fog. A preliminary report, never finalized, blamed those deaths on an influenza epidemic.

Emerging evidence revealed that only a fraction of the deaths could be from influenza. 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.

More recent research suggests that the number of fatalities was considerably greater than contemporary estimates, at about 12,000.

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 which produces minimal smoke. Central heating (using gas, electricity, oil or permitted solid fuel) was rare in most dwellings at that time, not finding favor 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.

Cause

Atmospheric scientists at Texas A&M University investigating the haze of polluted air in Beijing realized that their research led to a possible cause for the London event in 1952.

“By examining conditions in China and experimenting in a lab, the scientists suggest that a combination of weather patterns and chemistry could have caused London fog to turn into a haze of concentrated sulfuric acid.”

Even though research findings point in this direction, the two events are not identical. In China, the combination of nitrogen dioxide and sulfur dioxide, both produced by burning coal, with a humid atmosphere, created sulfates while building up acidic conditions that, left unchanged, would have stalled the reaction. However, ammonia from agricultural activity neutralized the acid allowing sulfate production to continue.

It is theorized that in 1952 in London, the nitrogen dioxide and sulfur dioxide combined with fog rather than humidity; larger droplets of water diluted the acid products, allowing more sulfate production as sulfuric acid. Sunrise burned off the fog, leaving concentrated acid droplets that killed citizens.

*This article uses material from the Wikipedia article Great Smog of London, which is released under the Creative Commons Attribution-ShareAlike License 3.0 (view authors).