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Scientists finally discover the cause of London’s deadly Great Smog of 1952

Scientists finally discover the cause of London’s deadly Great Smog of 1952

The Great Smog of 1952, also known as the Big Smoke or Killer Fog, was an event in London that killed 4,000 and sent 150,000 to the hospital.

In December 1952, a dense fog fell over London, one like no one had ever seen before. Over the course of four days, 150,000 people were sent to the hospital and 4,000 died as a result of this killer fog. The event became known as the “Great Smog” or the “Big Smoke,” and for the last 60 years and chane, scientists have been working to find out exactly what happened.

Until now that is.

An international group of researcher from China, the US, and the UK managed to recreate the killer fog in a laboratory setting, and they believe they finally know what happened back in 1952.

While scientists weren’t able to recreate the conditions before this, for years it has been understood that the fog was a reaction to the emissions caused by burning coal. While the exact chemical process remained a mystery, the event became a watershed moment in understanding the relationship between air quality and health. It led to government research into the environment, which in turn led to government regulations. Two years later the Clean Air Act of 1956 was passed, a legal framework which helped pave the way for countless environmental laws around the world.

The new study concludes that one of the primary factors behind the Great Smog was the chemical sulfate. The fog also contained sulfuric acid, a byproduct of the sulfur dioxide released from burning coal, but no one was sure exactly how the sulfuric acid was initially formed.

“Our results showed that this process was facilitated by nitrogen dioxide, another co-product of coal burning, and occurred initially on natural fog,” Renyi Zhang, an atmospheric scientist at Texas A&M and the lead author on the study wrote in a statement. “Another key aspect in the conversion of sulfur dioxide to sulfate is that it produces acidic particles, which subsequently inhibits this process.”

Zhang went on to explain that the natural fog that frequently creeps over London contains several larger, generally harmless particles that the smaller acidic particles can be distributed throughout. In 1952 the acidic particles spread via the fog. When the fog evaporated, a deadly acidic-haze was left in its place.

Part of the reason this study received new attention 64 years later is thanks to China. 16 of the 20 most polluted cities in the world are all Chinese, but there is a significant difference between the air pollution of 1952 and the air pollution of 2016. The particles in China’s smog are made up of nanoparticles rather than the relatively larger sulfuric acid from coal burning. For the killer fog and the creation of sulfate, the atmosphere also needs ammonia. The chances of the killer fog returning are fairly low, but the research was an illuminating look at air pollution in general, reagarless of the era.

“In China, sulfur dioxide is mainly emitted by power plants. Nitrogen dioxide is from power plants and automobiles, and ammonia comes from fertilizer use and automobiles,” Zhang said. “Again, the right chemical processes have to interplay for the deadly haze to occur in China. Interestingly, while the London fog was highly acidic, contemporary Chinese haze is basically neutral.”

The team is confident that the mystery of the London fog of 1952 that killed thousands has been solved, and China has some new ideas on improving its air quality. As long as history doesn’t repeat itself, we should be able to avoid a repeat of the Great Smog.



Founder and DBP boss. Ryan likes the Kansas Jayhawks, long walks on the beach, and high fiving unsuspecting people.