The 2013 Clean Air Action of the Chinese government implemented aggressive emission controls to decrease air pollution. Fine particulate matter (PM2.5)Â concentrations across China fell by 30-50% over the 2013-2018 period and this can be largely attributed to decreases in emissions of SO2 and primary organic PM2.5. However, surface ozone pollution increased over the same period and this may be driven chemically by the decrease in PM2.5Â. The next phase of Clean Air Action should implement an effective two-pollutant strategy for continuing to decrease PM2.5Â while reversing the increase in ozone. Climate change may help to decrease the frequency of severe pollution events in China in the future by decreasing the relative humidity.
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