Widespread stratospheric intrusion influence on summer ozone pollution over China revealed by multi-site ozonesonde and validated EAC4 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 10 to 13 June 2013, based on ozonesondes from Beijing, Changchun, and Hong Kong, and validated O3 reanalysis products. Ozonesondes from Beijing indicated notable upper-level secondary O3 peaks (> 400 ppbv) since 11 June. Tropospheric sub-high O3 layers were observed in Changchun on 12 June (> 120 ppbv) and Hong Kong on 13 June (> 80 ppbv). Nationwide surface measurements recorded severe O3 pollution (> 100 ppbv) from western plateaus to eastern plains over China. Together, these observations suggest a widespread influence of stratospheric O3 intrusion. Further, the ozonesonde-validated EAC4 reanalysis reproduced the fine-scale SI structure (O3-rich “tongue”), in turn well explaining the secondary O3 peaks and sub-high O3 layers in ozonesonde observations. The O3-rich “tongue” swept through the Tibetan Plateau on 10 June, triggering extreme O3 pollution with a stratospheric 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 entrained into the surface layer, exacerbating surface O3 pollution occurred in eastern China on 13 June, with a stratospheric O3 contribution of 3–15 ppbv (2 %–10 %). This research underscores the importance of multi-site ozonesondes in understanding stratospheric O3 intrusions and the potential of the publicly available EAC4 reanalysis in multiyear SI analyses.