In 1952, a killer fog containing pollutants covered London for five days, causing breathing problems and killing thousands of residents. The exact cause and nature of the fog has remained mostly unknown for decades, but scientists now believe the mystery has been solved.
The same air chemistry also happens in China and other locales, they report.
In December of 1952, the fog enveloped all of London and residents at first gave it little notice because it appeared to be no different from the familiar natural fogs that have swept over Great Britain for thousands of years.
But over the next few days, conditions deteriorated, and the sky became dark. Visibility was reduced to only three feet in many parts of the city, all transportation shut down, and tens of thousands of people had trouble breathing. By the time the fog lifted on December 9, at least 4,000 people had died and more than 150,000 had been hospitalized. Thousands of animals in the area also died.
Recent British studies now say that the death count was likely far higher—more than 12,000 people of all ages died from the killer fog. It has long been known that many of those deaths were likely caused by emissions from coal burning, but the exact chemical processes that led to the deadly mix of fog and pollution have not been fully understood over the past 60 years.