I was recently re-watching the Netflix series "The Crown" ahead of the new season. I was reminded of a weather-centered episode during the first season, which depicts the beginning of Queen Elizabeth's reign. London was smothered by smog for five days in December 1952. 100,000 were struck with respiratory illnesses and thousands died due to this weather event.
We associate dangerous weather with a strong low that may bring storms, heavy snow, or fierce winds. The Great Smog of London was triggered by clear skies and high pressure. Skies were clear the morning of December 5th. A veil of fog developed, not unusual for London. The fog eventually enshroud some famous landmarks. Within a few hours the fog turned to a sickly color as it mixed with smoke and soot that was pumped into the air by London’s factories, chimneys, and automobiles.
The fog had turned to "smog." Smog is a type of air pollution created by industrial output and naturally occurring weather patterns. This particular "pea soup" continued to thickened into a poisonous stew over the city that lingered for five days.
The smog was exacerbated by cold temperatures which forced people to burn more coal for heat. London's geography and the weather contributed to the smog. A high pressure system had stalled over southern England and a cold air mass blanketed the region. A large river valley around the city limited air circulation. The cold air trapped the valley's warmer air leading to the development of a temperature inversion. A typical atmospheric temperature profile would show colder temperatures higher above the surface. When the temperature increases in a layer above cooler air near the ground, a temperature inversion forms. This warm layer traps the air beneath, preventing it from rising, and leading to a stagnant air mass.
A temperature inversion prevented the smog from rising. In the case of London in early December 1952, visibility diminished and air quality worsened as the soot-laden smog grew thicker day by day.
The Great Smog paralyzed London and crippled transportation for five days. The smog was so thick that residents were unable to see just a few feet in front of them. Soccer matches were cancelled. People were advised to stay indoors. Still thousands became ill. It is estimated that at least 4,000, and up to 12,000 people died due to illnesses caused by the Great Smog. The pattern finally changed on December 9th when a brisk wind swept the toxic cloud away from London and out to the North Sea.
It took years after the Great Smog for Parliament to pass the Clean Air Act of 1956. This restricted the burning of coal in urban areas. Homeowners received grants to convert from coal to another heat source. It would take several more years before the city's primary heating source transitioned to gas, oil, and electricity. During that time deadly fogs periodically occurred, including one that killed about 750 people in 1962.
The United States had a similar incident occur in Donora, Pennsylvania in 1948. A deadly smog smothered the small town in southwestern Pennsylvania for five days. 20 people died and it caused respiratory problems for 6,000 people of the 14,000 population. This is one event that lead to passage of the Clean Air Act in the U.S.