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Levels of harmful air pollution over China have been falling steadily since 2015, due to stricter controls on emissions. China鈥檚 air is still terribly polluted, but the reduction has probably prevented 150,000 premature deaths per year.

鈥淚t鈥檚 probably the fastest any country has improved their air quality ever,鈥� says Ben Silver at the University of Leeds in the UK. 鈥淏ut it鈥檚 still really bad.鈥�

Silver and his colleagues tracked levels of tiny particles, called PM2.5, using data from over 1600 monitoring stations dotted around China. In line with previous studies, they found that levels of PM2.5 declined from 2015 to 2017.

Other researchers had expressed concern that the apparent decline in pollution might be nothing to do with falling emissions, but due to changes in weather patterns, which can affect where pollutants build up. So the team used a model of the air over China, which simulated wind patterns and the chemistry of the pollution.

They ran the model twice, once with a decline in emissions after 2015 and another with no decline. The latter model saw little change in pollution levels, suggesting weather changes alone couldn鈥檛 be responsible for the decline. 鈥淲e showed the weather was a relatively small effect, compared to emissions reductions,鈥� says Silver.

The most important source of China鈥檚 air pollution is industry, followed by people burning fuel for cooking and heating in their homes, power generation, transport and agriculture. 鈥淭he major decline has been in industry and power generation,鈥� says Silver. 鈥淭hat鈥檚 usually the easiest thing to target, because you have big point sources like factories.鈥�

It is difficult to determine how many people are killed by air pollution, and how many would be saved by cutting it. 鈥淵ou can鈥檛 ever isolate a single death and say 鈥楶M2.5 killed this person鈥�,鈥� says Silver. Instead, epidemiologists treat it as a risk factor for early death.

The team estimates that China鈥檚 PM2.5 reductions have cut annual premature deaths by 150,000. But this is far from a complete victory. 鈥淓ven though it鈥檚 declined a lot, there鈥檚 still a huge health impact,鈥� says Silver. The team estimates there were still 2.65 million deaths linked to PM2.5 in 2017.

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