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Abstract Tropospheric ozone pollution poses a major environmental challenge in China. As its primary natural source, Stratosphere-to-Troposphere Transport (STT) has been recognized as a significant contributor to tropospheric ozone in western, northeastern, and eastern China. However, the extent of STT’s influence on southeastern China has been less studied due to data limitations. Using a recently available one-year dataset of ozonesonde observations from a regional background station, we find that STT contributes significantly to tropospheric and surface ozone elevation in southeastern China. Our results show that STT plays a more substantial role in shaping tropospheric ozone during spring than previously believed, accounting for over 30% of ozone concentrations above 4 km. Without the stratospheric contribution, the spring seasonal peak almost disappears. STT can also significantly influence ozone concentrations at the surface. For example, a distinct ozone profile was observed on 4 May 2022, with a notable increase in tropospheric ozone. This tropospheric ozone increase was caused by a STT event triggered by a robust horizontal trough and subsequent southward movement of subtropical jets in the upper troposphere. According to a stratospheric tracer derived from an atmospheric chemistry model, this STT event contributed to 25%–30% of the surface ozone increase. Overall, this study highlights the important role of STT in driving tropospheric ozone variations, even in regions with comparatively lower ozone levels in southeastern China.
Hong et al. (Wed,) studied this question.