中国芳香族二次有机气溶胶半显式氧化生成机制改进与模拟OA

Aromatic secondary organic aerosol(SOA)is a key component of fine particulate matter in urban areas of China,contributing significantly to air pollution.In this study,a semi-explicit aromatic oxidation scheme(SXP)was implemented in the atmospheric chemistry module of the Earth System Model to better represent the oxidation processes of anthropogenic aromatic volatile organic compounds(VOCs).The SXP scheme explicitly simulates the competition between RO2 autoxidation and termination reactions and is used to evaluate the contribution of autoxidation to aromatic SOA formation.Compared with the default model(BASE)that uses the volatility basis set(VBS),the simulation results of the SXP scheme reduces the average bias in surface SOA concentrations by approximately 5%.The differences between the simulation results of SXP and BASE show distinct regional and seasonal patterns,with SXP simulating higher SOA levels in southern China and during the summer months.Mechanistic analysis indicates that the differences arise primarily from the influence of NOx on aromatic SOA formation.Under low-concentration NO conditions(<15 ppbv),SXP simulates 20%～50%higher aromatic SOA compared to BASE.In contrast,under high-concentration NO conditions(>25 ppbv),SXP simulates approximately 10%lower SOA levels than BASE.This is due to the inclusion of the competition between RO2 autoxidation and NO termination reactions,where high NO concentrations suppress autoxidation and reduce SOA formation efficiency.Finally,the study examines changes in aromatic SOA during 2013-2019,a period of significant emission reductions in China.The results provide insights into the trends of anthropogenic SOA under NOx reduction scenarios,helping to improve understanding of the impact of NO on aromatic SOA formation and its regional distribution.This work underscores the importance of accounting for the competition between autoxidation and NO termination reactions in accurately predicting SOA formation in response to emission controls.