The Chinese city of Linfen and the Great Smog of London are separated by half a world and more than half a century but they are linked by a common killer. On Wednesday night, levels of hazardous sulphur dioxide in Linfen, Shanxi province, surged to more than 1,000 micrograms per cubic metre. The pollution persisted until Thursday morning, hitting a peak of 1,303 micrograms. That compares to the World Health Organisation’s recommendation that people should not be exposed to more than 500 micrograms per cubic metre for more than 10 minutes or 20 micrograms over 24 hours. Like PM2.5 – the small smog particles most hazardous to human health – sulphur dioxide can worsen chronic respiratory diseases and poison lungs. It is a major component of air pollution but not as closely watched. What goes into our lungs when we breathe in China’s severe smog? But Li Ting, a meteorology postdoctorate researcher at the Chinese Academy of Sciences, noticed the numbers released by the city’s environmental bureau and raised the alarm, comparing the appalling conditions to those in the British capital in December, 1952. During the Great Smog severe air pollution enveloped London for about five days and killed at least 4,000 people. Tens of thousands more are thought to have been sickened by the pollution. One of the main contaminants over the five days was the 370 tonnes of sulphur dioxide that had been released into the air, according to the British national weather service. Li said in a Weibo post that sulphur dioxide was especially dangerous if it combined with suspended PM2.5 particles and entered people’s lungs, as was the case in the deadly London smog. Her post was shared more than 39,000 times and attracted more than 8,000 comments by last night. “I work in Linfen and always feel that the smog problem in the city is much worse than that in Beijing. But the local government and the public have almost been blind to that,” one commenter said. Chinese media demand action on smog as Christmas brings more pollution Linfen has already been told to clean up its act. The Shanxi Environmental Protection Bureau warned Linfen authorities on December 21 that the level of sulphur dioxide in most of the city had exceeded 600 micrograms per cubic two days earlier and was above 1,100 micrograms at one monitoring station, or 17 times the nationwide 60 microgram limit. The bureau demanded Lifen identify the major source of the sulphur dioxide pollution and take action to reduce its concentration in the air as much as possible. The city’s environmental protection bureau said it was still looking for the reasons of the unusually high sulphur dioxide concentrations and would report as soon as possible, the Beijing Youth Daily reported. In Linfen, the average concentration of sulphur dioxide over the past month was above 800 micrograms per cubic metre, which was five times more than China’s maximum limit of 150 micrograms for sulphur dioxide. During the same period, the city’s average readings of PM2.5 were close to the hazardous level of 500 micrograms per cubic metre.