Scientists Uncover Mystery Behind the 1952 Killer Fog in London

A team of international scientists has uncovered the mechanism behind the mysterious killer fog that sweep across London for five days in December 1952.

Their findings, described in a paper published in the journal Proceedings of the National Academy of Sciences, showed that the deadly haze in London was caused by right chemical processes interplaying with each other.

"People have known that sulfate was a big contributor to the fog, and sulfuric acid particles were formed from sulfur dioxide released by coal burning for residential use and power plants, and other means," explained Renyi Zhang, a scientist at Texas A&M University and lead author of the study, in a statement. Our results showed that this process was facilitated by nitrogen dioxide, another co-product of coal burning, and occurred initially on natural fog.

As the sulfur dioxide converts to sulfate, the process produces acidic particles. Natural fog contained larger particles of sulfate, while the acidic particles formed were sufficiently diluted. As the larger particles in the fog evaporate, the smaller acidic haze particles were left covering the city.

For the study, the researchers conducted thorough laboratory experiments and atmospheric measurements in China. The researchers observed that the chemistry of the killer fog was similar to what often occurs in China. The only difference is that the haze starts from much smaller nanoparticles in China. Additionally, ammonia is necessary for the sulfate formation process in China's fog. The researchers also observed that the London fog was highly acidic, while the contemporary haze in China is basically neutral.

The killer fog that covered the city in 1952 is said to kill more than 12,000 people of all ages and sent over 150,000 people to the hospitals. Thousands of animals were also killed by the fog. The high mortality rate of the killer fog led to the passage of the Clean Air Act in 1956 by the British Parliament. Until now, the 1952 fog is still considered as the worst air pollution event in the European history.