The Great London Smog
Back in December 1952, a veil of deadly fog rolled over the city of London. Locals paid little attention to it at first, but the sky took a yellowish hue and started to smell like rotten eggs. Within a day, the air was green and smelled like garbage. Visibility got poorer and poorer, and breathing outside became painful. In the five days that this lasted, 150,000 people had been hospitalized and over 12,000 people died. It was the deadliest air pollution disaster in British history. It jumpstarted the the environmental movement, which led to the passage of some of the first clean air laws. For years, nobody figured out what caused it, until now.
London’s “Great Smog” was blamed on coal, and not without reason. Yet the details of what exactly happened have eluded experts for decades. Yet through lab experiments and atmospheric measurements of two Chinese cities know for pollution – Xi’an and Beijing – a team of experts have worked out a likely explanation, which they published in the Proceedings of the National Academies of Sciences.
A major part of the Great Smog was sulfate, particles of sulfuric acid that both smell bad and are harmful. In their study, researchers demonstrated that in naturally foggy conditions, sulfate will build up inside water droplets from chemical interactions between sulfur dioxide and nitrogen dioxide, both of which come out of burning coal. Sulfate also helps promote the formation of other particles, such as nitrate and organic matter, which exacerbates the development of severe haze. As the water in fog dries up, the acid becomes concentrated, leaving corrosive haze particles that coats everything from sidewalks to human lungs.
Similar chemistry is responsible for smoggy skies in both Beijing and Xi’an. Although in these cities, other chemicals play a role too. The study suggests that the conditions behind this infamous event can happen anywhere in the world.
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