While most talk of air pollution these days seems to focus on developing and industrializing nations such as China and India, one of the worst cases of industrial pollution in human history occurred in London in the early twentieth century. London relied on coal for much of its power, and there were no regulations on the amount of emissions coal plants could produce until 1956. In December 1952, a particularly bad fog rolled into London and shrouded the city in thick smog for four days. As the fog receded, it left thousands dead and hundreds of thousands more seriously ill in its wake.
This event, referred to as “The Great Smog” or “The Big Smoke,” has puzzled climatologists and other scientists for decades. It was generally assumed that emissions from coal plants combined with the naturally-occurring fog to produce the deadly smog, but the exact mechanism for this has not been fully understood. Until now, that is. Researchers from Texas A&M University believe they have finally unravelled the mystery of London’s “Great Smog.”
Researchers began this study by looking into the causes of the toxicity in Beijing’s notoriously bad smog. As they looked into other cases of toxic air pollution, they began to notice similarities with the London Fog of 1952. In a Texas A&M press release, head researcher Renyi Zhang claims that certain sulfuric byproducts of coal burning actually can combine with fog particles to form the equivalent of airborne sulfuric acid, which could explain the highly lethal effects of the London Fog:
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 […] 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 their published data, the researchers claim that sulfur dioxide produced as a result of industrial activity is the main culprit behind the toxicity and haziness of severe smog in heavily polluted areas like China’s perpetually-gray capital, Beijing:
Under polluted environments, this SO2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development.
The researchers hope that this study can not only shine light on the causes of London’s deadly “Big Smoke,” but also help reduce air pollution toxicity worldwide.