Atmospheric oxidizing capacity in autumn Beijing: Analysis of the O3 and PM2.5 episodes based on observation-based model
2023
Jia, Chenhui | Tong, Shengrui | Zhang, Xinran | Li, Fangjie | Zhang, Wenqian | Li, Weiran | Wang, Zhen | Zhang, Gen | Tang, Guiqian | Liu, Zirui | Ge, Maofa
Atmospheric oxidizing capacity (AOC) is the fundamental driving factors of chemistry process (e.g., the formation of ozone (O₃) and secondary organic aerosols (SOA)) in the troposphere. However, accurate quantification of AOC still remains uncertainty. In this study, a comprehensive field campaign was conducted during autumn 2019 in downtown of Beijing, where O₃ and PM₂.₅ episodes had been experienced successively. The observation-based model (OBM) is used to quantify the AOC at O₃ and PM₂.₅ episodes. The strong intensity of AOC is found at O₃ and PM₂.₅ episodes, and hydroxyl radical (OH) is the dominating daytime oxidant for both episodes. The photolysis of O₃ is main source of OH at O₃ episode; the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) plays important role in OH formation at PM₂.₅ episode. The radicals loss routines vary according to precursor pollutants, resulting in different types of air pollution. O₃ budgets and sensitivity analysis indicates that O₃ production is transition regime (both VOC and NOₓ-limited) at O₃ episode. The heterogeneous reaction of hydroperoxy radicals (HO₂) on aerosol surfaces has significant influence on OH and O₃ production rates. The HO₂ uptake coefficient (γHO₂) is the determining factor and required accurate measurement in real atmospheric environment. Our findings could provide the important bases for coordinated control of PM₂.₅ and O₃ pollution.
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