Impact of Molecular Chlorine Production from Aerosol Iron Photochemistry on Atmospheric Oxidative Capacity in North China
Qianjie Chen, Xuan Wang, Xiao Fu, Xinxin Li, Becky Alexander, Xiang Peng, Weihao Wang, Men Xia, Yue Tan, Jian Gao, Jianmin Chen, Yujing Mu, Pengfei Liu, Tao Wang
Abstract
Elevated levels of atmospheric molecular chlorine (Cl 2 ) have been observed during the daytime in recent field studies in China but could not be explained by the current chlorine chemistry mechanisms in models. Here, we propose a Cl 2 formation mechanism initiated by aerosol iron photochemistry to explain daytime Cl 2 formation. We implement this mechanism into the GEOS-Chem chemical transport model and investigate its impacts on the atmospheric composition in wintertime North China where high levels of Cl 2 as well as aerosol chloride and iron were observed. The new mechanism accounts for more than 90% of surface air Cl 2 production in North China and consequently increases the surface air Cl 2 abundances by an order of magnitude, improving the model’s agreement with observed Cl 2 . The presence of high Cl 2 significantly alters the oxidative capacity of the atmosphere, with a factor of 20–40 increase in the chlorine radical concentration and a 20–40% increase in the hydroxyl radical concentration in regions with high aerosol chloride and iron loadings. This results in an increase in surface air ozone by about 10%. This new Cl 2 formation mechanism will improve the model simulation capability for reactive chlorine abundances in the regions with high emissions of chlorine and iron.