In 1952, post-war London was a bustling city that relied primarily on coal, both to generate power and to heat homes. It had been a particularly cold Fall, and Londoners were burning more coal than usual to keep themselves warm.
The type of coal they were burning was a low-grade sulfurous kind, similar to lignite coal, because the better-quality "hard" coals, such as anthracite coal, were being exported. This increased the amount of sulfur dioxide in the coal smoke.
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There were numerous coal-fired power stations in the Greater London area, and they emitted each day: 1,000 tons of smoke particles, 2,000 tons of carbon dioxide, 140 tons of hydrochloric acid, 14 tons of fluorine compounds, and 370 tons of sulfur dioxide. Adding to all that was pollution from car exhausts, steam locomotives, diesel buses and industrial sources.
On December 4, 1952, a weather phenomenon called an anticyclone settled in. It caused a temperature inversion, with cold, stagnant air trapped under a layer, or "lid", of warm air. The resultant fog mixed with smoke from chimneys, particulates from exhausts, and other pollutants to form smog. Smog is fog that has soot in it.
On Friday, December 5, 1952, Londoners woke up to yellow-black air and near zero visibility, making driving difficult or impossible. Road, rail and air transport ceased. Ambulances were unable to transport people to the hospital.
If walking during the day was difficult, at night it was impossible because street lights at that time were incandescent bulbs which were unable to penetrate the smog.
It Seeped Indoors
The smog was so dense that it seeped indoors, causing concert venues and movie theaters to close. While there was no panic, hospitals were soon overrun, with most of the victims being the very young or the elderly.
Victims experienced difficulty breathing, chest pains, lung inflammation, the onset of asthma, and a lack of oxygen in the bloodstream due to carbon monoxide.
150,000 people were hospitalized, and in London's East End, death rates during that period were nine times normal. On December 8th and 9th, the death rate peaked at 900 per day. Undertakers ran out of coffins and florists ran out of flowers. Ultimately, some 12,000 people died as a result of the smog.
Most of the deaths were caused by respiratory tract infections, such as bronchopneumonia and acute purulent bronchitis, from hypoxia (a lack of oxygen), and as a result of mechanical obstruction of the air passages. Twice the number of infants as usual died during the week of the smog. Many victims died in their beds from asphyxiation.
The shocking death toll led to new regulations restricting the use of dirty fuels in industry and banning black smoke. The 1956 Clean Air Act authorized local councils to set up smokeless zones and make grants to householders to convert their homes from coal fires to gas, oil, or electricity. The 1968 Clean Air Act called for the use of tall chimneys for industries burning coal, liquid or gaseous fuels.
It wasn't until 2016, when scientists from Texas A&M University were investigating smog in Beijing and Xi'an, China that they determined a possible cause for the London event. They concluded that the London smog was comprised of concentrated sulfuric acid.
It is theorized that in 1952 in London, the nitrogen dioxide and sulfur dioxide combined with the fog, and water droplets diluted the acid, allowing more sulfate production as sulfuric acid. The sun then burned off the upper layers of the fog, leaving concentrated acid droplets. Breathing in acid aerosol irritated the bronchial tubes, which produced large amounts of mucus and became inflamed. It is estimated that the pH of the air was as low as 2.
Researchers consider the 1952 London smog the worst air pollution event in European history.