Seasonal simulation and source apportionment of SO42− with integration of major highlighted chemical pathways in WRF-Chem model in the NCP

Abstract

Particulate sulfate (SO₄²⁻) is the major component of fine particles in the North China Plain (NCP). It plays an essential role in the entire atmosphere and climate system. Accurately reproducing the SO₄²⁻ levels is challenging for chemical transport model. Here, the major highlighted multiple phase SO₄²⁻ formation pathways are integrated into the WRF-Chem model and seasonal model performance of SO₄²⁻ are assessed by observed SO₄²⁻ at multiple sampling sites located in the NCP. The results show that the integration of these SO₄²⁻ formation pathways obviously narrow the gap between simulation and observation in autumn, winter, and summer at three sampling sites in the NCP, for high RH conditions facilitate the hygroscopic growth of PM_2.5 and promote the multiple phase reaction to form SO₄²⁻. The underestimation in autumn, winter, and summer may ascribe to the missed SO₄²⁻ source from photo-induced chemical route and missed hygroscopicity of organic aerosols. The obviously discrepancy between simulation and observation in spring may ascribe to the large underestimation of SO₂ levels and lack consideration of dust scheme. Source apportionment results show that the gas phase reaction played a vital role in the formation of SO₄²⁻ in each season. The contribution of aqueous phase SO₂ oxidation by H₂O₂ is higher in autumn and summer due to simultaneously high RH levels and stronger photochemical reaction activity. The Mn(II) catalytic SO₂ oxidation pathway at the particle interface is important in autumn and make greater contribution to SO₄²⁻ formation during winter severe haze events under extremely high RH levels.