Written by Émilie St-Hilaire, Four Green Steps

During December 1952, London experienced one of the worst smog episodes ever recorded.  With the industrial revolution in the 19th century, many big cities of Britain saw their level of air pollutants increase. Due to specific conditions, the smog that covered London in 1952 settled for a few days was so dense that it caused many deaths and health problems.

Winter started off very cold in December 1952, causing London citizens to burn more coal to heat their homes. At that time, coal was the major source of heating. Combined with the usual industrial emissions, the coal combustion caused the accumulation of sulphur dioxin, black soot and tar particles in the air.

On December 5fth, a light ordinary fog formed over the city. During the night however, climatic conditions such as cool air, few winds and high ground humidity, caused the light fog to turn into thick and dense smog. A temperature inversion caused the smog to settle at ground level.

In a temperature inversion, the cool, denser air is below the warmer air, so it does not move upwards and remains stuck to the ground.  The sun would normally have warmed up the ground in the morning, cancelling the inversion.  But the sun could not reach the ground to heat it due to the thickness of the smog, so the cold layer of dense smog stayed at ground level. Visibility was reduced to a few meters only. The smog had a black-yellow color. The water from the fog condensed around soot and tar particles, and reacted with the sulphuric acid to form acid rain.

The fog cleared out on December 9th. During the period between the 5th  and the 9th of December, 1000 tonnes of smoke particles, 2000 tonnes of carbon dioxide, 140 tonnes of hydraulic acid, and 14 tonnes of fluorine were released in the atmosphere. The particle concentration in the air 56 times the normal level.

About 12 000 people died from complications due to the smog, including tuberculosis, heart diseases and respiratory diseases- bronchitis, asthma, pneumonia. Young children and elderly were most affected. Many people developed  respiratory problems.

In 1956 and 1968, the Clean Air Acts were introduced to reduce air pollution by promoting the use of smokeless fuels for residential and industrial uses. We can still observe smog episodes in London and other big industrial cities, but it is nothing close to the smog episode of December 1952.

Image courtesy of Creative Commons.

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