Modeling Study on the Impacts of Mineral Dust Photocatalytic Heterogeneous Chemistry on the Sulfur Removal Over East Asia

Abstract

Dust heterogeneous chemistry substantially influences the atmosphere and has profound impacts on our environment and climate. Gas-particle partitioning on dust not only modifies species' chemical evolutions but also influences their deposition velocity. However, how does dust heterogeneous chemistry impacts acid deposition remains unexplored. In this research, we integrated dust photocatalytic mechanism into GEOS-Chem to assess its impact on sulfur removal across various regions and time spans in China. We find the photocatalytic mechanism enhances simulation performances of acid deposition. Observational validation demonstrates significant reductions in modeling bias for sulfur dioxide (SO₂) dry deposition and sulfate (SO₄) total deposition. Additionally, the improved model captures the declining trend of SO₄ deposition over 2006–2020. We further identified two key impacts of photocatalytic chemistry: firstly, our findings indicate it enhances sulfur removal more efficiently in near-desert areas like North China Plain (NCP) than in downwind areas like Yunnan-Guizhou-Chongqing region (YGY). Lifetimes of total sulfur reduced from 3.29 to 2.46 days in NCP, and from 2.46 to 1.95 days in YGY. This discrepancy results from faster conversion of SO₂ to dust-phase SO₄ and larger proportions of coarse-mode particles in NCP, resulting in accelerated SO₄ deposition velocity. Secondly, our results indicate that because dust photocatalytic chemistry amplifies removal of sulfur through SO₄ formation and deposition, decreased dust emission resulted in enhanced sulfur lifetimes over 2006–2014. Sensitivity experiments further show higher dust concentrations accelerate pollutants' removal. These findings underscore the importance of dust heterogeneous chemistry in influencing sulfur deposition, providing scientific insights for mitigating acid deposition in China.