Scientists finally know what caused London's 'killer fog' - Business Insider: “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 micrometres in size, and the acid formed was sufficiently diluted. Evaporation of those fog particles then left smaller acidic haze particles that covered the city.”
Similar things are happening in China’s most polluted cities right now. The reason there hasn’t been an incident like London’s “killer fog” is down to chemical happenstance: China uses a lot of fertiliser and that, combined with the heavy road traffic, results in high levels of ammonia, which�neutralises the particles. “The right chemical processes have to interplay for the deadly haze to occur in China,” explained Zhang. “While the London fog was highly acidic, contemporary Chinese haze is basically neutral.”
Similar things are happening in China’s most polluted cities right now. The reason there hasn’t been an incident like London’s “killer fog” is down to chemical happenstance: China uses a lot of fertiliser and that, combined with the heavy road traffic, results in high levels of ammonia, which�neutralises the particles. “The right chemical processes have to interplay for the deadly haze to occur in China,” explained Zhang. “While the London fog was highly acidic, contemporary Chinese haze is basically neutral.”