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The Lethal London Smog Event
5th-9th December 1952


The 1952 London smog episode (also known as the Great Smog or Great Smoke) stands out as one of the worst man-made air pollution disasters the world had ever known given the sheer number of people who died as a result.

Even though London was well known for its frequent smog, no one had ever seen a smog of such magnitude.

For the week ending 13th December 1952, there was approximately 4,000 excess deaths (i.e. the number of deaths exceeding those during the same time period the previous year when there was minimal smog) and an additional 8,000 deaths occurred over the next two and a half months.

London smog in December 1952
© Copyright N T Stobbs and licensed for reuse
under this Creative Commons Licence

This smog event made the public acutely aware that smoky air can kill, but the government at the time was reluctant to do anything to prevent future smog until public demand for action became too great. Consequently, four years later in 1956, extensive government legislation was passed through parliament that would ultimately lead to substantial reductions in fossil fuel emissions in large cities, not only in London, but across the modern world.


You may be asking, how did it all begin?...

Well, you have to look back in history.

History of air pollution in London

There has always been episodes of thick smog permeating the streets of London ever since the mid-to-late thirteenth century when shipped 'sea coal' was burnt and used as a fuel by limeburners and other industries. Most of the people living in London (population estimated to be 80,000) in around the year 1300 used firewood and it was not until after 1550 that coal began to be widely used for domestic purposes. Even back in the thirteenth century, local residents complained to the authorities that the smoke pouring forth from the lime kilns stunk. In fact, Queen Eleanor of Provence, (wife of King Henry III) back in 1257 became quite ill due to the high levels of coal fumes permeating into Nottingham Castle, that she was forced to leave.

As the years rolled by, especially in the latter part of the Victoria Era, London smog levels gradually became worse since nearly every household was now burning coal instead of firewood. This meant that the emissions produced by coal burning could now uniformly fall upon parts of London that normally were not exposed to smog.

The winters of 1873,1880,1882,1891 and 1892 recorded exceptionally thick smog and many people and animals died due to complications from severe respiratory problems when they inhaled high doses of carbon monoxide, toxic particulate matter (soot) mixed with sulfur dioxide.

By the turn of the 20th Century, severe London smog episodes became less common since the meteorological conditions that aided the formation of the late 19th century smog events were not present. The next significant air pollution event in London would not occur until November 1948. This lesser known smog contributed to the deaths of between 700 and 800 people.


Health effects of the London smog event of 1952

Ever since the 1952 London smog event, there has been numerous studies proving that inhaling high levels of air pollutants endangers your health. Unfortunately, for the residents of London, no one including the government officials realised this link. In fact, up to 1952, it was widely believed that people became sick or died as a result of the unusually cold weather conditions, rather than the smog being the cause of the problem.

The most common health complaint at the time was that the smog left a sulphurous taste in the mouth and it irritated the nasal passages and made the eyes sting. The smog made breathing difficult and caused many healthy people to suffer respiratory problems. These symptoms became a lot worse in people who had a pre-existing medical condition.

What was immediately apparent after the smog had cleared was the fact that this smog not only led to the deaths of people with pre-existing medical problems (respiratory and cardiovascular) but it also contained sufficient doses of toxic substances that contributed to the death of healthy individuals.

The highest recorded polycyclic aromatic hydrocarbon (PAH) concentration during the worst part of the London smog event was measured to be 3300ng/m3*. Airborne PAH's are highly toxic are known to be both animal and human carcinogens. It makes you wonder what percentage of people who were exposed to the London smog episode actually developed various types of cancers. This, of course, is impossible to know.

* Please note: 1ng means one nanogram which is equal to 10-9grams

As a comparison, the highest recorded PAH concentration measured from January 1991 to December 1992 is 10.2ng/m3.


It's no wonder the number of excess deaths reached 4,000 people since high levels of PAH's rapidly weaken human immune systems, and thus the additional inhaled carbon monoxide (CO) and sulphur dioxide (SO2) together with particulate matter (smoke) placed their already compromised bodies at grave risk of developing severe respiratory and cardiovascular complications.

According to a number of researchers, it was concluded that the smog contained a large amount of metallic particulate matter (most notably zinc). Now zinc is highly soluble and is responsible for damaging cells in the body. It is highly possible that the high proportion of zinc particles in the air was readily absorbed into the bloodstream and that contributed to their death.

As you are probably aware, when taken orally at low doses, zinc tablets can be quite therapeutic if you suffer from a zinc deficiency, yet the same substance is toxic at high doses.

Up until recently, it was widely believed that an influenza outbreak was responsible for additional 8,000 deaths that occurred within the first two months after the smog had first disappeared. The latest research has shown that there was no evidence of this influenza outbreak.



So what was the cause of the 1952 London smog episode?

This smog event culminated into the worst civilian disaster in terms of loss of life. There was multiple factors at play that led to the tragic London smog episode on the 5-9th December 1952. These factors can broken into:

  1. Non-industrial:

    • According to the 1952 census records, Greater London now had a population of about 8.6 million. A large percentage of the population were trying to keep warm and so needed to burn coal in their domestic grates. This factor is believed to be the main contributor to the 1952 London smog episode.


  2. Meteorological:

    • There was a strong slow moving high pressure system situated over southern England. This guarantees that there would be no wind to blow the smog away from the regions of London that were pumping out air pollutants.

    • A strong temperature inversion developed in the early hours of the 5th December 1952. A temperature inversion prevents the natural vertical dispersal of air pollutants into the atmosphere.

    • Outdoor temperatures plummeted to near freezing and remained so throughout the whole period.
    • The relative humidity rose to almost 100 percent during the night of the 6th December 1952 and remained at high levels until the evening of the 9th December. This moist cold air drained into all parts of low lying London.


  3. Industrial:

    • There was a build up of toxic substances into the atmosphere through the combustion of coke, oil and coal products due to the large number of factories in operation throughout London.


  4. Vehicles:

    • In July 1952, electric trams were replaced by thousands of diesel-powered buses. This was the first time in history that London air was exposed to high levels of diesel emissions. By the third day of the London smog, no one could see to drive since the air pollution made the visibility exceptionally low (particularly in the mornings). Thus, diesel emissions stopped.
    • Even though there was numerous cars on the road in the days leading to the smog event, it has been shown that car exhaust fumes made only a minor contribution up until the third day of the 1952 London smog episode.



Main air pollutants during the London smog episode

Air pollutant
Emission rate
(tonnes/day)
Smoke particles
1000
Sulphuric acid
(H2SO4)
800
Sulphur dioxide
(SO2)
370
Hydrochloric acid
(HCl)
140
Fluorine compounds
(F)
14


Now if you combine all these factors, the only logical conclusion is that London smog event of 1952 was inevitable. The main reason why the smog was so bad is because there was no wind movement and thus the pollutants continued to build to toxic levels. The worst day in terms of visibility and extreme toxicity occurred on the morning of the 7th December. Visibility outdoors had reduced to less than one metre during the night and around 20-100 metres during the afternoon.

As a consequence, it was impossible to use public transport and most shop owners closed doors since they didn't want the outdoor smog to permeate indoors. However, it was impossible to prevent the tiny soot and other smog particles from entering most houses. This explains why there were large numbers of people dying at home.

The 1952 London smog event dwarfed all previous smog events in London in terms excess mortality and morbidity. Thankfully, given that air pollution emissions today are regulated across most of the industrialised nations, it's extremely unlikely that a repeat of what happened in London will ever occur again. But even so, the people living in London nowadays still have to be aware that the current levels of air pollution can still affect human health.




References

  1. Anderson HR. Air pollution and mortality:A history. Atmospheric Environment. 2009;43:142-152.

  2. Bell ML, Davis DL and Fletcher T. A retrospective assessment of mortality from the London smog episode of 1952: The role of influenza and pollution. Environmental Health Perspectives 2004;112(1):6-8.

  3. Brimblecombe P. History of air pollution. In: Singh HB. (Ed.) Composition, Chemistry and Climate of the Atmosphere. Van Nostrand Reinhold. New York. 1995;pp. 1-18.

  4. Brimblecombe P. The Big Smoke. A History of Air Pollution in London Since Medieval Times. Methuen. London. 1987

  5. Davis D. The great smog. History Today. 2002;52(12):2-3.

  6. Fenger J. Air pollution in the last 50 years - From local to global. Atmospheric Environment. 2009;43:13-22.

  7. Galloway JA, Keene D and Murphy M. Fuelling the city: production and distribution of firewood and fuel in London's region, 1290-1400. Economic History Review. 1996;XLIX(3):447-472.

  8. Weinhold B. Heavy on the metals. Environmental Health Perspectives. 2003;111(9):A481.



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