Effect of cloud chemistry on seasonal variations of sulfate and its precursors in China

Abstract

Cloud chemistry is of paramount importance in the secondary production of atmospheric aerosols, influencing the spatial-temporal distribution of gases and aerosols in the atmosphere. Using WRF/CUACE (China Meteorological Administration Unified Atmospheric Chemistry Environment), this study assesses the seasonal impacts of cloud chemistry on the concentrations of SO₂, sulfate, as well as two oxidizers, H₂O₂ and O₃, in the most east-central areas of China, including four key pollution zones (the North China Plain (NCP), the Yangtze River Delta (YRD), the Pearl River Delta (PRD), and the Sichuan Basin (SCB)). Near the surface, H₂O₂-oxidation was the dominant pathway for cloud chemistry in four key pollution zones in four seasons. H₂O₂ consumption is most pronounced in summer, especially in the SCB and NCP, while O₃ consumption peaks in autumn, particularly in the PRD and southeastern coastal areas. While at higher altitudes, oxidation by O₃ and H₂O₂ is compatible with the cloud chemistry process. Near the surface, cloud chemistry consumes SO₂ ranging from approximately 0.1 ppb–5.0 ppb, resulting in the generation of about 6.0–25.0 μg m⁻³ of sulfate. Higher SO₂ reduction and sulfate increase are in both summer and winter, especially for the SCB and NCP in summer, and the SCB in winter. Vertically, the cloud chemistry process primarily concentrates its influence on SO₂ and sulfate concentrations below 5 km, particularly within the turbulent zone of the troposphere below 2 km in all the four pollution zones and four seasons. The most notable seasonal variation occurs in the NCP compared to other zones. This study also shows that cloud chemistry effectively improves the seasonal simulation accuracy of SO₂ and sulfate, resulting in improved correlation and a notable reduction in RMSE.