The Great Smog Descended on London More Than 65 Years Ago, and Took Almost as Long to Solve

A tugboat on the Thames near Tower Bridge in heavy smog, 1952.
A tugboat on the Thames near Tower Bridge in heavy smog, 1952.
Fox Photos/Hulton Archive/Getty Images

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.

5th December 1952: Morning traffic at Blackfriars, London almost at a standstill because of the blanket smog.Don Price/Fox Photos/Getty Images

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.

Heavy smog in Piccadilly Circus, London, 6th December 1952.Central Press/Hulton Archive/Getty Images

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.

A London bus makes its way along Fleet Street in heavy smog, 6th December 1952.Edward Miller/Keystone/Hulton Archive/Getty Images

“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.

Mid-morning smog, as seen from the embankment at Blackfriars, London, 5th December 1952.Monty Fresco/Topical Press Agency/Hulton Archive/Getty Images

Fans of the Netflix series The Crown will likely remember the season 1 episode in which Queen Elizabeth and then-Prime Minister Winston Churchill 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.”

Large numbers of people using the underground system to get around London during a period of heavy smog, which hampered transport on the roads, 8th December 1952.Keystone/Hulton Archive/Getty Images

In addition to helping to solve a troubling environmental disaster that had confounded scientists for decades, Zhang and his colleagues’ research is also helping 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.”

A man guiding a London bus through thick fog with a flaming torch.Monty Fresco/Getty Images

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, the Queen enacted the Clean Air Act 1956, which banned the burning of pollutants across the UK.

Mental Floss's Three-Day Sale Includes Deals on Apple AirPods, Sony Wireless Headphones, and More

Apple
Apple

During this weekend's three-day sale on the Mental Floss Shop, you'll find deep discounts on products like AirPods, Martha Stewart’s bestselling pressure cooker, and more. Check out the best deals below.

1. Apple AirPods Pro; $219

Apple

You may not know it by looking at them, but these tiny earbuds by Apple offer HDR sound, 30 hours of noise cancellation, and powerful bass, all through Bluetooth connectivity. These trendy, sleek AirPods will even read your messages and allow you to share your audio with another set of AirPods nearby.

Buy it: The Mental Floss Shop

2. Sony Zx220bt Wireless On-Ear Bluetooth Headphones (Open Box - Like New); $35

Sony

For the listener who likes a traditional over-the-ear headphone, this set by Sony will give you all the same hands-free calling, extended battery power, and Bluetooth connectivity as their tiny earbud counterparts. They have a swivel folding design to make stashing them easy, a built-in microphone for voice commands and calls, and quality 1.18-inch dome drivers for dynamic sound quality.

Buy it: The Mental Floss Shop

3. Sony Xb650bt Wireless On-Ear Bluetooth Headphones; $46

Sony

This Sony headphone model stands out for its extra bass and the 30 hours of battery life you get with each charge. And in between your favorite tracks, you can take hands-free calls and go seamlessly back into the music.

Buy it: The Mental Floss Shop

4. Martha Stewart 8-quart Stainless-Steel Pressure Cooker; $65

Martha Stewart

If you’re thinking of taking the plunge and buying a new pressure cooker, this 8-quart model from Martha Stewart comes with 14 presets, a wire rack, a spoon, and a rice measuring cup to make delicious dinners using just one appliance.

Buy it: The Mental Floss Shop

5. Jashen V18 350w Cordless Vacuum Cleaner; $180

Jashen

If you're obsessive about cleanliness, it's time to lose the vacuum cord and opt for this untethered model from JASHEN. Touting a 4.3-star rating from Amazon, the JASHEN cordless vacuum features a brushless motor with strong suction, noise optimization, and a convenient wall mount for charging and storage.

Buy it: The Mental Floss Shop

6. Evachill Ev-500 Personal Air Conditioner; $65

Evachill

This EvaChill personal air conditioner is an eco-friendly way to cool yourself down in any room of the house. You can set it up at your work desk at home, and in just a few minutes, this portable cooling unit can drop the temperature by 59º. All you need to do is fill the water tank and plug in the USB cord.

Buy it: The Mental Floss Shop

7. Gourmia Gcm7800 Brewdini 5-Cup Cold Brew Coffee Maker; $120

Gourmia

The perfect cup of cold brew can take up to 12 hours to prepare, but this Gourmia Cold Brew Coffee Maker can do the job in just a couple of minutes. It has a strong suction that speeds up brew time while preserving flavor in up to five cups of delicious cold brew at a time.

Buy it: The Mental Floss Shop

8. Townew: The World's First Self-Sealing Trash Can; $90

Townew

Never deal with handling gross garbage again when you have this smart bin helping you in the kitchen. With one touch, the Townew will seal the full bag for easy removal. Once you grab the neatly sealed bag, the Townew will load in a new clean one on its own.

Buy it: The Mental Floss Shop

9. Light Smart Solar Powered Parking Sensor (Two-Pack); $155

FenSens

Parking sensors are amazing, but a lot of cars require a high trim to access them. You can easily upgrade your car—and parking skills—with this solar-powered parking sensor. It will give you audio and visual alerts through your phone for the perfect parking job every time.

Buy it: The Mental Floss Shop

10. Liz: The Smart Self-Cleaning Bottle With UV Sterilization; $46

Noerden

Reusable water bottles are convenient and eco-friendly, but they’re super inconvenient to get inside to clean. This smart water bottle will clean itself with UV sterilization to eliminate 99.9 percent of viruses and bacteria. That’s what makes it clean, but the single-tap lid for temperature, hydration reminders, and an anti-leak functionality are what make it smart.

Buy it: The Mental Floss Shop

Prices subject to change.

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links. If you haven't received your voucher or have a question about your order, contact the Mental Floss shop here.

Absentee Ballot vs. Mail-In Ballot: What’s the Difference?

Liliboas/iStock via Getty Images
Liliboas/iStock via Getty Images

Since you mail in an absentee ballot, it seems like mail-in ballot is just a convenient alternative for people who always forget the word absentee. And though the terms are often used interchangeably, there is technically a difference.

Up until the Civil War, American voters were generally required to vote at their local polling stations in person. But when states realized this would prevent hundreds of thousands of soldiers from voting in the 1864 presidential election, they started passing laws to let them send in their ballots instead. As The Washington Post explains, state legislatures have since broadened these laws to include other citizens who can’t make it to the polls on Election Day: people who are traveling, people who have disabilities, people attending college away from home, etc. Because these voters are all physically absent from the polls for one reason or another, their ballots are known as absentee ballots.

Some states require you to meet certain criteria in order to qualify for an absentee ballot, while others don’t ask you to give a reason at all (which is known as “no-excuse absentee voting”). Since this year’s general election is happening during a pandemic, many states have temporarily adopted a no-excuse policy to encourage everyone to vote from home. But even if you don’t need to provide an excuse, you do usually need to request an absentee ballot.

According to Dictionary.com, mail-in ballot is a more general term that can refer to any ballot you send in. It’s often used when talking about all-mail voting, when states send a ballot to every registered voter—no request necessary. Oregon and a few other states actually conduct all elections like this, and several other states have decided to do it for the upcoming presidential election. But even though you don’t have to send in an application requesting a mail-in ballot in these situations, you do still have to be registered to vote.

Because voting processes are mostly left up to the states, there’s quite a bit of variation when it comes to what officials call ballots that you don’t cast in person. You could see the term mail-in ballot—or vote-by-mail ballot, or advanced ballot, or something similar—on an application for an absentee ballot, and you could hear absentee ballot used in a conversation about all-mail voting.

No matter what you call it, you should definitely mail one in for this election—here’s how to do that in your state.