Efficacy of China's clean air actions to tackle PM2.5 pollution between 2013 and 2020

Beginning in 2013, China launched two phases (2013-2017 and 2018-2020) of clean air actions that have led to substantial reductions in PM2.5 concentrations. However, improvement in PM2.5 pollution was notably slowing down during Phase II. Here we quantify the efficacy and drivers of PM2.5 improvement and evaluate the associated cost during 2013-2020 using an integrated framework that combines an emission inventory model, a chemical transport model and detailed cost information. We found that national population-weighted mean PM2.5 concentrations decreased by 19.8 mu g m(-3) and 10.9 mu g m(-3) in the two phases, and the contribution of clean air policies in Phase II (2.3 mu g m(-3) yr(-1)) was considerably lower than that of Phase I (4.5 mu g m(-3) yr(-1)), after excluding the impacts from meteorological condition changes and COVID-19 lockdowns. Enhanced structure transitions and targeted volatile organic compounds and NH3 reduction measures have successfully reduced emissions in Phase II, but measures focusing on the end-of-pipe control were less effective after 2017. From 2013 to 2020, PM2.5 abatement became increasingly challenging, with the average cost of reducing one unit of PM2.5 concentration in Phase II twice that of Phase I. Our results suggest there is a need for strengthened, well-balanced, emission control strategies for multi-pollutants.