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

Ground-level ozone (O 3 ) pollution has recently become of increasing concern in China. Studies have shown that conventional models often fail to predict accurately the net O 3 production rate ( P (O 3 ) net ) due to the absence of certain mechanisms, particularly the kinetics from missing reactive volatile organic compounds (VOCs) species, and hence affects the reliability of evaluation for O 3 formation sensitivity (OFS). Therefore, we conducted a field observation of P (O 3 ) net and OFS using a P (O 3 ) net (NPOPR) detection system based on a dual-channel reaction chamber technique at the Guangdong Atmospheric Supersite of China in Heshan, Pearl River Delta (PRD) in autumn of 2023. The in-situ monitoring data were then 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 HO 2 uptake by ambient aerosols, dry deposition, N 2 O 5 uptake, and ClNO 2 photolysis, and found that the discrepancies between the modelled P (O 3 ) net ( P (O 3 ) net _Mod) and measured data ( P (O 3 ) net _Mea) did not change evidently, the maximum daily P (O 3 ) net differed by ∼ 44.8 %. Meanwhile, we found that the agreement of OFS assessment results between the direct measurements and the modelling study was lower in the P (O 3 ) net rising phase (08:00–09:00 LT, 63.6 %) than in the P (O 3 ) net stable phase (10:00–12:00 LT, 72.7 %) and P (O 3 ) net declining phase (13:00–17:00 LT, 72.7 %). The results in this study reflected that unmeasured oxygenated VOCs (OVOCs) were the most effective compensating factor for the discrepancies between observed and computed P (O 3 ) net and OFS, hinting clearly at the importance of quantitative understanding the total reactivity of VOCs in O 3 chemistry.