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.
Highlights
Aerosol pH is normally estimated using thermodynamic models, such as E-AIM(Clegg et al, 1998)and ISORROPIA II, due to the limitations of direct aerosol pH measurement techniques(Fountoukis andNenes, 2007; Hennigan et al, 2015)
Seasonal variations in aerosol pH were mainly driven by the temperature, while the diurnal variations were driven by both temperature and relative humidity
Besides the effect of reduction in SO42− (Fu et al, 2015; Xie et al, 2020), our results suggest that the change in NVCs may play an important role in determining the trend of aerosol pH
Summary
Aerosol pH is normally estimated using thermodynamic models, such as E-AIM(Clegg et al, 1998)and ISORROPIA II, due to the limitations of direct aerosol pH measurement techniques(Fountoukis andNenes, 2007; Hennigan et al, 2015). 6(Pye et al, 2020; Zheng et al, 2020; Su et al, 2020). Aerosols in the United States are highly acidic, with pH values of approximately 1–2(Guo et al, 2015; Nah et al, 2018; Pye et al, 2018; Zheng et al., 2020). Aerosols in mainland China and Europe have similar average aerosol acidity levels Aerosol pH exhibits notable spatial and temporal variability, which is affected by changes in factors such as temperature, relative humidity (RH), and aerosol compositions(Pye et al, 2018; Nenes et al., 2020a; Tao et al, 2020; Zheng et al, 2020). Very few studies have investigated the trend and spatial variability of aerosol pH and its drivers. Weber et al(Weber et al, 2016) showed that aerosols tend to remain highly acidic upon the reduction of SO42− during summertime in the southeastern United States
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