The Great Smog Descended on London 70 Years Ago, and Took Almost as Long to Solve

Heavy fogs have long been a part of life in London. In his novel Bleak House, Charles Dickens wrote:

“Fog everywhere. Fog up the river where it flows among green airs and meadows; fog down the river, where it rolls defiled among the tiers of shipping, and the waterside pollutions of a great (and dirty) city ... Chance people on the bridges peeping over the parapets into a nether sky of fog, with fog all round them, as if they were up in a balloon and hanging in the misty clouds.”

Yet a full 100 years after the celebrated author wrote those words, the city would become enveloped in a dangerous mix of fog and smoke—the likes of which they had never experienced, and were not prepared for. When the smog finally lifted, thousands of people were dead. And it would take nearly 65 years for scientists to pinpoint the reason for what has become known as The Great Smog of 1952, one of the deadliest environmental disasters in the history of the world.

December 5, 1952 started out just like any other day in London, albeit a tremendously foggy one. But as the day wore on, it became clear that there was something different about the darkness that had descended on the city, which would hang there until December 9. People who were caught outside in the weather found themselves gasping for air, barely able to open their eyes from the sting the smoky atmosphere was delivering. Those who could see couldn’t see very far; as visibility dwindled to practically zero, pedestrians had trouble seeing their own feet while motorists were forced to abandon their vehicles.

For several days, the city was essentially shut down. It all began with a cold front, which led more and more Londoners to crank up their coal stoves and gather around them for warmth. While the smoke from the city’s chimneys would normally disperse into the atmosphere, a lack of wind and an unfortunately timed anticyclone positioned over the city ended up trapping the smoke, which mixed with the fog and other pollutants, creating a lethal atmosphere.

“You had this swirling,” funeral director Stan Cribb told NPR in 2002, “like somebody had set a load of car tires on fire.” Cribb, who at the time was working as a mortician’s assistant, was on his way to a wake with his uncle—who was also his boss—with a line of mourners behind them. According to NPR:

"Neither man knew a catastrophe was brewing. They didn't know that a mass of stagnant air had just clamped a lid over London, trapping the smoke from millions of residential coal fires at ground level.

Cribb remembers being stunned by the blackness of the gathering fog. After a few minutes he couldn't see the curb from his spot behind the wheel. After a few more minutes, Tom Cribb got out and started walking in front of the hearse, to keep his nephew on the road. He carried a powerful hurricane lantern in one hand, but it was useless.

'It's like you were blind,' says Cribb."

When the fog finally lifted, reports estimated that at least 4000 people had been killed and 150,000 were hospitalized, though in the years since the total death toll has risen to approximately 12,000.

Fans of the Netflix series The Crown will likely remember the season 1 episode in which Queen Elizabeth (played by Claire Foy) and then-Prime Minister Winston Churchill (portrayed by John Lithgow) were forced to contend with the deadly event. (Of course, always aiming for accuracy, director Stephen Daldry told Entertainment Weekly that they weren’t about to use CGI to recreate The Great Smog. “We had to get a great, huge warehouse and fill it full of fog to create the great pea soup of 1952,” Daldry said. “We did it for real—CG didn’t look good enough for us.”)

Amazingly, it wasn't until 2016 that a global team of scientists announced that they may have finally solved the mystery of The Great Smog, and published their findings in the November 2016 issue of Proceedings of the National Academy of Sciences (PNAS).

“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,” Dr. Renyi Zhang, a professor at Texas A&M University and one of the paper’s lead authors, said. “But how sulfur dioxide was turned into sulfuric acid was unclear. 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.”

In addition to helping to solve a troubling environmental disaster that had confounded scientists for decades, Zhang and his colleagues’ research also helped to determine how to best deal with similar air pollution problems today, including those faced by several cities in China, which is home to some of the world’s most polluted cities.

“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. 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 government has pledged to do all it can to reduce emissions going forward, but it will take time,” he added. “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.”

Though it would be hard to call it a silver lining, The Great Smog of 1952 did have one positive effect: It forced the country’s government, and its people, to become more aware of the impact their actions had on their environment. On July 5, 1956, less than four years after London was enveloped in a lethal darkness, Parliament enacted the Clean Air Act 1956, which banned the burning of pollutants across the UK.

A version of this story ran in 2017; it has been updated for 2022.