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Mystery of London’s killer fog solved: Researchers reveal how chemicals combined to form acidic haze that killed 12,000 in 1952

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  • The deadly 1952 event is thought to have caused more than 12,000 deaths
  • It’s known that coal burning was to blame, but processes were a mystery
  • Study has now found that sulfuric acid particles mixed with natural fog
  • This diluted the particles and created an acidic haze that covered the city 

In 1952, a mysterious fog swept through London, blanketing the city in a dense layer of pollutants that killed thousands of people and animals and made it difficult to breathe for days.

While the exact cause has long remained unknown, an international team of researchers now says its solved the mystery – and the same air chemistry can be seen today in China and other areas.

In a new analysis, the researchers have pinpointed the chemical processes that combined with natural fog as a result of coal burning, eventually creating a deadly acidic haze that turned the sky completely dark.

Researchers have pinpointed the chemical processes that combined with natural fog as a result of coal burning, eventually creating a deadly acidic haze that turned the sky completely dark

Researchers have pinpointed the chemical processes that combined with natural fog as a result of coal burning, eventually creating a deadly acidic haze that turned the sky completely dark

THE KILLER FOG REVEALED

Using data from modern pollution in China, researchers have determined that the catastrophic event was the result of sulfuric acid particles mixing with natural fog to cover the entire city.

According to the researcher, a similar chemistry frequently occurs in modern China, which hosts 16 of the world’s most polluted cities.

When the fog first rolled through in December of 1952, residents took little notice; fogs have long enveloped the city.

But in the days to follow, visibility was reduced to just three feet in some areas, transportation was shut down, and thousands of people suffered from breathing problems.

After the devastating event, it was thought that at least 4,000 people had died, along with thousands of animals, and more than 150,000 people were hospitalized.

Now, using data from modern pollution in China, researchers have determined that the catastrophic event was the result of sulfuric acid particles mixing with natural fog to cover the entire city.

‘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,’ says Renyi Zhang, University Distinguished Professor and the Harold J. Haynes Chair of Atmospheric Sciences and Professor of Chemistry at Texas A&M University.

‘But how sulfur dioxide was turned into sulfuric acid was unclear.

LONDON’S KILLER FOG: THE HAZE THAT KILLED 12,000

Pictured, a London bus makes its way along Fleet Street in heavy smog, 6th December 1952

Pictured, a London bus makes its way along Fleet Street in heavy smog, 6th December 1952

The deadly fog first rolled in during December of 1952.

It enveloped London in a thick blanket of pollutants, reducing visibility to just three feet in some areas and causing transportation to shut down.

According to researchers, the sky during this time turned completely dark and thousands of people suffered from breathing problems.

The fog finally lifted on December 9, but at the time, it was thought that at least 4,000 people had died, along with thousands of animals, and more than 150,000 people were hospitalized.

Later studies, however, estimate that the death count may actually have exceeded 12,000.

While it’s long been known that coal burning was the cause, researchers have struggled to identify the exact chemical processes that made this event, also known as the Great Smog of 1952, so deadly.

When the fog first rolled through in December of 1952, residents took little notice; fogs have long enveloped the city. The image reveals heavy smog in Piccadilly Circus, London, 6th December 1952

When the fog first rolled through in December of 1952, residents took little notice; fogs have long enveloped the city. The image reveals heavy smog in Piccadilly Circus, London, 6th December 1952

‘Our results showed that this process was facilitated by nitrogen dioxide, another co-product of coal burning, and occurred initially on natural fog.

‘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.’

According to the researcher, a similar chemistry frequently occurs in modern China, which hosts 16 of the world’s most polluted cities.

A man feels his way cautiously from the pavement to the Underground in Westminster in 1952, battling through the haze that enveloped the city.

A man feels his way cautiously from the pavement to the Underground in Westminster in 1952, battling through the haze that enveloped the city.

But, China’s pollution problem is not exactly the same.

The country has experienced massive industrial and manufacturing growth over the past few decades, and the emissions largely come from power plants, automobiles, and fertilizers.

‘The difference in China is that the haze starts from much smaller nanoparticles, and the sulfate formation process is only possible with ammonia to neutralize the particles,’ Zhang said.

‘In China, sulfur dioxide is mainly emitted by power plants, nitrogen dioxide is from power plants and automobiles, and ammonia comes from fertilizer use and automobiles.

Charles Chaplin (Charlie Chaplin, 1889-1977) pictured with his wife Oona (1926-1991) on the roof of the London hotel (unnamed) where they were staying in 1952.Behind them, the haze is clearly visible

Charles Chaplin (Charlie Chaplin, 1889-1977) pictured with his wife Oona (1926-1991) on the roof of the London hotel (unnamed) where they were staying in 1952.Behind them, the haze is clearly visible

‘Again, the right chemical processes have to interplay for the deadly haze to occur in China. Interestingly, while the London fog was highly acidic, contemporary Chinese haze is basically neutral.’

The 1952 event is considered to be the deadliest air pollution event in European history, and spurred the passage of the Clean Air Act in 1956 by British Parliament.

And, while China has been making attempts in recent years to cut back on its emissions, the researchers note that the poor air quality still often necessitates breathing masks during much of the day.

Tourists wearing masks in Temple of Heaven in haze-covered Beijing, China. Studies show pollution is causing the deaths of up to 500,000 people in the country a year.

Tourists wearing masks in Temple of Heaven in haze-covered Beijing, China. Studies show pollution is causing the deaths of up to 500,000 people in the country a year.

By solving the mystery of the London fog, they say they may also have uncovered insight that could help in China.

‘A better understanding of the air chemistry holds the key for development of effective regulatory actions in China,’ Zhang said.

‘The government has pledged to do all it can to reduce emissions going forward, but it will take time.

‘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.

‘Reduction in emissions for nitrogen oxides and ammonia is likely effective in disrupting this sulfate formation process.’

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