Reactive chlorine chemistry and coastal circulation dynamics can collectively influence ozone formation in coastal environments; however, their combined effects on vertically resolved ozone formation and redistribution remain poorly understood. In this study, paired WRF-Chem simulations with and without chlorine chemistry were conducted to investigate the vertical ozone response over the Pearl River Delta (PRD) during February 2023. Two contrasting circulation regimes were identified: a sea-breeze-dominant period (17–18 February) and a land-breeze-dominant period (19–26 February). Under both regimes, the chlorine-induced ozone response was vertically heterogeneous, with the strongest enhancement occurring in the 200–600 m layer and a substantially weaker response in the 0–200 m layer. Within the 200–600 m layer, reductions in total VOC concentrations accompanied by elevated HO₂ and RO₂ levels indicate that chlorine chemistry modified VOC oxidation pathways and promoted radical propagation conducive to ozone production. The more pronounced VOC depletion and radical response during the sea-breeze-dominant period were attributable to suppressed ventilation and enhanced precursor accumulation. The persistent vertical ozone contrast between the 200–600 m and 0–200 m layers, corroborated by downward transport signatures revealed in vertical cross-sectional analyses, suggests that ozone enriched in the elevated layer may contribute to near-surface ozone variability through vertical redistribution. Consistent vertically heterogeneous ozone structures were further identified across all nine PRD cities. These findings demonstrate that surface-level ozone measurements alone may inadequately characterize the full influence of chlorine chemistry in coastal boundary layers, and underscore the necessity of vertically resolved analyses of chemical and dynamical processes for a comprehensive understanding of coastal ozone pollution.

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