Assessment of Ozone Formation Sensitivity and Possible Bias Analysis in an Urban Ambient Environment Using a Direct Measurement Technique

Abstract Effectively identifying ozone (O 3 ) formation sensitivity to its precursors, volatile organic compounds (VOCs) and nitrogen oxides (NOx = NO + NO 2 ) are the key to developing effective O 3 pollution control strategies. However, assessments of photochemical O 3 formation can be significantly biased by neglecting certain photochemical reactions in existing atmospheric chemical mechanisms, which in turn markedly influence the determination of O 3 formation sensitivity (OFS). This study improved a dual‐channel net photochemical ozone production rate ( P (O 3 ) net , NPOPR) detection system to measure OFS continuously in Dongguan, a typical industrial city in China. Three OFS regimes were identified by comparing P (O 3 ) net levels in a base ambient air scenario to those with added NOx/VOCs—VOC‐limited (37.5%), NOx‐limited (12.5%), and transition (50.0%)—with notable differences observed in radical chain lengths and CO/HCHO ratios. Daily patterns showed a transition regime in the early morning, shifting to the NOx‐limited regime in the afternoon. Measured and modeled OFS showed approximately 50% agreement, with modeled OFS often overestimating VOC‐limited regimes. Further analysis indicated that unmeasured oxygenated VOCs (OVOCs) with high photolysis frequencies and anthropogenic VOCs (such as branched alkenes) act as important sources of missing VOCs reactivities, which are potential contributors to the estimation bias of OFS. This study emphasizes the importance of comprehensive VOCs measurement for accurate OFS estimation through modeling methods, thereby offering valuable insights for developing effective O 3 pollution control policies.