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Abstract

Aerosol acidity plays a key role in regulating the chemistry and toxicity of atmospheric aerosol particles. The trend of aerosol pH and its drivers are crucial in understanding the multiphase formation pathways of aerosols. Here, we reported the first trend analysis of aerosol pH from 2011 to 2019 in eastern China. The implementation of the Air Pollution Prevention and Control Action Plan leads to −35.8 %, −37.6 %, −9.6 %, −81.0 % and 1.2 % changes of PM2.5, SO42−, NHx, NVCs and NO3− in YRD during this period. Different from the fast changes of aerosol compositions due to the implementation of the Air Pollution Prevention and Control Action Plan, aerosol pH shows a moderate change of −0.24 unit over the 9 years. Besides the multiphase buffer effect, the opposite effects of SO42− and non-volatile cations changes play key roles in determining the moderate pH trend, contributing to a change of +0.38 and −0.35 unit, respectively. Seasonal variations in aerosol pH were mainly driven by the temperature, while the diurnal variations were driven by both temperature and relative humidity. In the future, SO2, NOx and NH3 emissions are expected to be further reduced by 86.9 %, 74.9 % and 41.7 % in 2050 according to the best health effect pollution control scenario (SSP1-26-BHE). The corresponding aerosol pH in eastern China is estimated to increase by ~0.9, resulting in 8 % more NO3− and 35 % less NH4+ partitioning/formation in the aerosol phase, which suggests a largely reduced benefit of NH3 and NOx emission control in mitigating haze pollution in eastern China.