5 days of fog and 12,000 deaths in one of the world's largest cities: a look back at the crazy story of the Great Smog

© Elīna Arāja/Pexels

In the history of environmental disasters, the Great Smog in London is certainly one of the deadliest pollution episodes in history. The British capital was then a major industrial centre, with many coal-fired factories and power stations that emitted large quantities of fine particles, sulphur dioxide and other pollutants. The majority of its inhabitants also heated with coal; of very poor quality; to counter the harsh temperatures of the English winter.

This fuel, combined with a high population density and intense industrial activity, released large quantities of pollutants into the atmosphere, transforming the air into a veritable poison. Between Thursday, December 4 and Tuesday, December 9, 1952, the unthinkable happened: 12,000 people lost their lives and 100,000 became seriously ill. The Great Smog was a near-cataclysmic event that served as an exceptional textbook case for understanding urban air pollution phenomena.

Subscribe to Lemon Squeezer

Thermal inversion: the time bomb that asphyxiated London

To understand the episode of the Great Smog, it is necessary to First, analyze the weather conditions that London was experiencing at that time. On December 4, 1952, a particularly stable anticyclonesettled over the British capital. This weather system caused a characteristic thermal inversion: a layer of warm air at altitude, acting as a thermal cover, trapped a mass of cold air at ground level. Temperatures fell sharply, reaching -2 °C at the surface.

Thermodynamic studies carried out by the British Meteorological Office have highlighted an inverse temperature gradient up to 500 metres above sea level: the air warms by 2 ° C every 100 metres, contrary to the usual gradient of -1 °C/100. This unusual atmospheric configuration blocked any vertical dispersion of pollutants, creating a veritable chemical reaction chamber on an urban scale. The latter thus remained trapped at ground level, considerably increasing their concentration.

Air saturated with deadly pollutants

This was followed by a cascade of chemical reactions; sulfur dioxide (SO2), emitted massively by the combustion of domestic and industrial coal, underwent a series of transformations. Due to the presence of high atmospheric humidity and metal catalysts (mainly iron and manganese from industrial emissions), SO2 was oxidized to sulfur trioxide (SO3).

SO2 concentrations rapidly reached staggering levels: 3.4 ppm on average, with localized peaks of 4.2 ppm in some industrial areas. For reference, the current WHO standard sets the alert threshold at 0.5 ppm over one hour. Analyses of medical records have shown a perfect correlation between these concentrations and the spatial distribution of mortality.

The SO3 reacted instantly with water in the atmosphere to form sulfuric acid (H2SO4). This sulfuric acid, which is extremely corrosive, was one of the main causes of damage to the lungs and respiratory tracts of Londoners. It mixed with particles suspended in the air, forming acid aerosols.

The formation of secondary aerosols amplified the phenomenon. Soot particles, whose diameter varies between 0.1 and 10 µm (micrometers), served as condensation nuclei. They catalyzed the formation of suspended sulfuric acid droplets, creating a corrosive fog of an unbelievable density. In the most affected areas, you could not see more than 30 cm in front of you.

Result: Londoners were therefore breathing an extremely toxic mixture of air and this prolonged inhalation of irritants and corrosives had serious effects on their organisms. Cough, difficulty breathing, chest tightness, bronchitis, and in the most severe cases, pulmonary edema.

The eyes, throat and nasal passages have been particularly affected by the acidity of the air, causing conjunctivitis, rhinitis and pharyngitis. Fine particles have penetrated deep into the lungs and are in the bloodstream, increasing the risk of myocardial infarction and stroke. A real massacre.

The catastrophe forced the political world to act. Scientists, whose voices had until then been little listened to, were finally heard. Under pressure from public opinion, Parliament adopted theClean Air Act, marking a turning point in the country's energy policy. The introduction of smoke-free zones, strict control of industrial emissions and modernization of heating systems have led to a dramatic reduction in particulate emissions: – 76% in a decade, from an annual average of 250 μg/m³ to 60 μg/m³.

The Great Smog left an indelible mark on British history, but unfortunately, air pollution is still a current phenomenon. Many countries are still under threat of such dangerous episodes today. China, India and the countries of South-East Asia are particularly affected and megacities such as Delhi, Beijing or Jakarta are regularly plagued by episodes of extreme pollution. According to UNICEF: ” Air pollution has an increasingly significant impact on human health, constituting the second leading risk factor for death in the world […] and was the cause of 8.1 million deaths worldwide in 2021 “. Although progress has been made, we are still very far from claiming to breathe healthy air and even France is concerned, with ” 40 000 deaths attributable each year to fine particles ” according to Santé Publique France.

• The Great SmogThe 1952 London fog was caused by a combination of thermal inversion, industrial pollution and heavy coal use, creating an extremely toxic fog.
• The fog caused thousands of deaths and serious respiratory illnesses, due to fine particles and acidic compounds.
• The event led to major reforms to air quality in the UK, although pollution remains a critical global problem today.

📍 To never miss any Presse-citron news, follow us on Google News and WhatsApp.

[ ]