New research from Texas A&M University has claimed to solve certain mysteries behind the killer fog that descended on London in December 1952 – and it could help China tackle its ongoing pollution problem.
On 5 December, 1952, a sulphuric fog descended on London without warning, covering the city for around four days before it lifted. Studies have suggested that it killed over 12,000 people. More than 150,000 were hospitalised.
"People have known that sulphate was a big contributor to the fog, and sulphuric acid particles were formed from sulphur dioxide released by coal burning for residential use and power plants, and other means," said Renyi Zhang, a chemistry professor at the university.
"But how sulphur dioxide was turned into sulphuric 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 sulphur dioxide to sulphate 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."
Though the researchers have linked the findings to China's dangerous pollution problem, they say that the process is slightly different – with China's haze coming from much smaller particles that are first neutralised by ammonia. "Interestingly, while the London fog was highly acidic, contemporary Chinese haze is basically neutral," said Zhang.
China's growth in industry and manufacturing has led to air quality so poor that people regularly have to wear masks while outside.
The killer fog of London led to the country passing the Clean Air Act several years later. The study says that China will be able to deliver on promises to better the air quality by reducing emissions in nitrogen oxide and ammonia to stop the sulphate formation process.