Why observed and modelled ozone production rates and sensitives differ, a case study at rural site in China

Abstract. Ground-level ozone (O₃) pollution has recently become of increasing concern in China, traditional models often fail to accurately predict the net O₃ production rate (P(O₃)_net) and O₃ formation sensitivity (OFS) due to missing reactive volatile organic compounds (VOCs) and their complex reactions. Therefore, we conducted a field observation of P(O₃)_net and OFS using a P(O₃)_net (NPOPR) detection system based on a dual-channel reaction chamber technique at the Guangdong Atmospheric Supersite of China in Heshan, Pearl River Delta in autumn of 2023. The in-situ monitoring data were compared with results from a zero-dimensional model incorporating the Master Chemical Mechanism (MCM v3.3.1). We tested the model performance by incorporating parameterization for 4 processes including HO₂ uptake by ambient aerosols, dry deposition, N₂O₅ uptake, and ClNO₂ photolysis, and found that the discrepancies between the modelled and measured P(O₃)_net did not change evidently, the maximum daily P(O₃)_net differed by ~44.8 %. Meanwhile, we found the agreement of OFS assessment results between the direct measurements and the modelling was lower in the P(O₃)_net rising phase (08:00–09:00, 63.6 %) than in the P(O₃)_net stable/declining phase (10:00–17:00, 72.7 %). The only approach to fill the gap between observation and computation was to add possible unmeasured reactive VOCs, especially oxygenated VOCs (OVOCs) in box model, this was true for both P(O₃)_net and consequent OFS, highlighting the importance of quantitative understanding the total reactivity of VOCs in O₃ chemistry.