The "Great Smog" Was A Killer Fog That Blanketed London For Five Days

The morning of Dec. 5, 1952, a light veil of fog surrounded London—what else is new? However, an unusually chilly night had caused Londoners to crank up their coal stoves. As the day crept on, the skies grew dark with soot and the fog turned into an ominous yellow cloud of smog.

Related: The Cement On This Italian Building Actually Eats Smog

The Smog That Killed Thousands

This "Great Smog" continued for five crippling days, leaving the entire city gasping for air. Transportation shut down, citizens couldn't breathe, and by December 9, between 4,000 and 12,000 people died and 150,000 more were hospitalized. This led the British Parliament to pass the 1956 Clean Air Act, restricting coal burning in urban areas and declaring a number of smoke-free zones. The Great Smog is still considered the worst air pollution event in European history. But what made this particular smog so deadly?

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The exact cause of this killer fog remained largely unknown until November 2016. It was then that researchers at Texas A&M University studying similar smog in China uncovered information that might've solved the Great Smog's greatest mystery. While it's true that coal smoke itself is noxious, there's a specific chemical process that made this smog so toxic: the sulfur dioxide from the coal smoke turned into sulfuric acid. How in the world did this happen?

What Exactly Happened?

Scientists have long known that burning coal creates sulfur dioxide, but they discovered that nitrogen dioxide (another byproduct of burning coal) was also probably at play in the smog. These two elements can combine to create sulfates, but that process forms acidic particles that usually stop it from going too far. That's not true when you add fog. The large water particles in the fog diluted the acid, giving the two gases free rein to create sulfates. Then, when the fog evaporated, the acid was still there. That's how sulfuric acid was able to blanket London for five days.

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According to Texas A&M researcher Renyi Zhang, if governments reduce nitrogen oxide and ammonia emissions, they can successfully keep this sulfate formation process from happening in the future. His hope is that these findings will help countries like China form ideas on how to improve their air quality.

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China's Ionic Smog-Sucking Vacuum

Daan Roosegaarde wants to place a giant smog vacuum in a Beijing park.

Key Facts In This Video

  1. PM 2.5 is small enough to penetrate the soft tissue of the lungs and other organs. 01:38

  2. An ionic field charges the neutral floating small particles in a positive way and filters them out using the largest electronic vacuum cleaner in the world. 03:42

  3. The smog that is filtered out is compressed and created into jewelry. 05:03

Written by Curiosity Staff December 30, 2016

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