I wasn't alive in 1952, but my Grandfather was. He would often tell me about the 'Great Smog' that engulfed London. For four days that December, a fog descended on the city so thick that it apparently even came indoors, causing as many as 12,000 fatalities and 100,000 illnesses. The density of the pollution was such that it was apparently nearly impossible to drive, or to see more than a few meters in front of your face.

The Great Smog of 1952 in London. [File Photo: blog.sina.com.cn]

The cause of the Great Smog has long been known - most homes at the time were heated by burning coal, and a period of almost no wind caused the smoke from this to become trapped. Smog itself was a regular occurrence in London during the 1950s, but would normally dissipate quickly with the arrival of wind.

The mystery of the Great Smog has been - until now - how it managed to cause so much death and illness when similar hazes and fogs in modern day cities cause so much less damage.

Now, researchers at universities in Beijing and Xi'an in China, along with Texas in the USA, have solved this mystery.

Apparently, what made the Great Smog so lethal was the fact that the air was a moist fog - in which two chemicals from the burning of coal were able to mix. As the water particles in the fog burnt-off, tiny acidic particles were left that were particularly hazardous to lungs.

Armed with this information, the researchers hope that they'll be able to prevent such a deadly smog from ever occurring again.

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