The Mystery of London’s 1952 "Killer Fog" Finally Solved by Scientists
LONDON — A decades-old mystery surrounding the cause of a deadly fog that claimed thousands of lives has finally been unraveled by an international team of researchers.
The Great Smog of London, which blanketed the British capital for five days in December 1952, resulted in 12,000 deaths and over 150,000 hospitalizations. The catastrophe didn't just affect humans; thousands of animals also perished in what remains the UK's worst air pollution event.
Five Days of Darkness and Sulfur
On December 5, 1952, a period of intense cold caused sulfur particles to mix with coal smoke, creating a thick, yellow fog that reeked of rotten eggs. Visibility was so poor that Londoners reported being unable to see their own feet.
Total Shutdown: All transportation was paralyzed, except for the London Underground.
Chaos in the Streets: Birds collided with buildings, and crime surged as looters used the impenetrable gloom to escape.
The Aftermath: The smog only lifted on December 9, when cold winds pushed it toward the North Sea, eventually leading to the landmark 1956 Clean Air Act.
The Chemical Breakthrough
While it was long known that sulfate contributed to the disaster, the exact chemical process remained a mystery—until now. A team led by Renyi Zhang from Texas A&M University published their findings in the Proceedings of the National Academy of Sciences.
"People knew that sulfate was a key contributor, but how sulfur dioxide was transformed into sulfuric acid was unclear," Zhang stated.
The researchers discovered that the process was facilitated by nitrogen dioxide, another byproduct of coal burning, which initially reacted within natural fog droplets.
The Connection to Modern-Day China
By analyzing atmospheric conditions in China—home to 16 of the world's 20 most polluted cities—the team confirmed similar chemical patterns. However, there is a crucial difference:
London: The 1952 fog was highly acidic.
China: The smog is neutral, thanks to ammonia (from fertilizers and vehicles) which neutralizes the particles.
This discovery not only solves a historical enigma but also provides vital data for modern cities struggling with air quality, proving that the right mix of nitrogen dioxide and sulfur dioxide can turn common fog into a lethal hazard.
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