By Patrick Jones, Buzz60
When you think of London you probably imagine some fog resting over the city.
For an outsider it seems like a charming adjective to a great city, however that wasn't always the case.
In 1952, a fog settled over the city for five days in December.
When it finally went away, there were more than 150,000 people hospitalized and more than 4,000 people dead.
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The fog was toxic, but the specifics of how or why it was toxic weren't fully understood until now.
Scientists from the U.K., U.S. and China looked into the matter in the hopes of preventing another such event.
The results of the study point the finger at coal burning. The lead researcher said sulfur dioxide, which is a byproduct of coal burning, was turned into sulfuric acid in the fog when it got trapped.
This was apparently happening because nitrogen dioxide, another by-product of coal burning, also got trapped in the fog facilitating the deadly chemical transition.
When the fog lifted, it left an acidic haze over the city.
This is scary in places like China where coal burning is still the norm. Hopefully this new research will lead to changes before we witness another tragedy.