Widespread stratospheric intrusion influence on summer ozone pollution over China revealed by multi-site ozonesonde, ground-based measurement and fully-validated reanalysis

Abstract. Understanding stratospheric intrusion (SI) is crucial for elucidating atmospheric complexities and improving strategies to mitigate surface ozone (O₃) pollution. This study investigates a deep trough-induced SI event in China from June 10 to 13, 2013, based on ozonesondes from Beijing, Changchun, and Hong Kong, nationwide ground-based measurements, and fully-validated reanalysis products. Ozonesondes from Beijing indicated notable high-level secondary ozone peaks (> 400 ppbv) since June 11. Tropospheric sub-high ozone layers were observed in Changchun on June 12 (> 120 ppbv) and Hong Kong on June 13 (> 80 ppbv). Nationwide surface ozone measurements recorded severe ozone pollution (> 100 ppbv) from western plateaus to eastern plains over China. Together, these observations suggest a widespread influence of stratospheric ozone intrusion. Further, the ozonesonde-validated EAC4 reanalysis reproduced the fine-scale SI structure (O₃-rich “tongue”), in turn well explaining the secondary ozone peaks and sub-high ozone layers in ozonesonde observations. The O₃-rich “tongue” swept through the Tibetan Plateau on June 10, triggering extreme ozone pollution with a stratospheric ozone contribution up to 30 ppbv (>30 %). With the trough’s eastward movement, the O₃-rich “tongue” penetrated into the lower troposphere of eastern China, and then be entrained into the surface layer, exacerbating severe ozone pollution occurred in the Northern China Plain on June 13, with a stratospheric ozone contribution of 3–15 ppbv (2–10 %). This research underscores the importance of multi-site ozonesondes in understanding stratospheric ozone intrusions and the potential of the publicly available EAC4 reanalysis in multiyear SI analyses.