Mystery Of London’s Killer Fog Has Finally Been Solved

The Great Smog of 1952 has finally been explained.

London's killer fog of 1952
The Big Smoke London's killer fog of 1952. Image Getty

It’s one of the great British mysteries of the early 20th century – why was London blanketed with a thick fog in December 1952?

During a five-day period, the fog turned acidic, killed 4,000 people and left 150,000 more in hospital with major respiratory problems. The long term effects were even more devastating – around 12,000 people died, and that’s not even taking into account animals and plant life.

As reported by IFLScience, a new study published in the Proceedings of the National Academies of Sciences seeks to get to the bottom of the mystery once and for all.

We’ve known for years that this fog – which turned a yellow-black colour and smelt disgusting – originated from industrial pollution that burned out sulfur dioxide. However, nobody’s been able to figure out why it turned into deadly sulfuric acid.

London's killer fog of 1952

This new study brought together scientists from China, US and the UK to mimic the London fog in a lab and compare it to similarly polluted Chinese cities, Beijing and Xi’an.

“Our results showed that this process was facilitated by nitrogen dioxide, another co-product of coal burning, and occurred initially on natural fog,” said Renyi Zhang of Texas A&M University.

“Another key aspect in the conversion of sulfur dioxide to sulfate is that it produces acidic particles, which subsequently inhibits this process.

“Natural fog contained larger particles of several tens of micrometers in size, and the acid formed was sufficiently diluted. Evaporation of those fog particles then left smaller acidic haze particles that covered the city.”

London's killer fog of 1952

He continued: “We think we have helped solve the 1952 London fog mystery and also have given China some ideas of how to improve its air quality.”

China’s heavy use of ammonia in fertilisers will apparently help neutralise these effects and prevent a new ‘Big Smoke’, the name given to London’s environmental disaster, from ever hitting Asia.

That pea-soup coloured fog and smell will still be around (just not in the deadly acid form).

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