03 May 2024
 | 03 May 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Tracing the origins of stratospheric ozone intrusions and their impacts on Central and Eastern China: a long-term study of direct and indirect pathways

Kai Meng, Tianliang Zhao, Yongqing Bai, Le Cao, Ming Wu, Xuewei Hou, and Yuehan Luo

Abstract. The impact of stratospheric intrusions (SIs) on Central and Eastern China (CEC) with severe ozone pollution presents a range of uncertainties, underscoring the imperative for sustained research endeavors. In this study, we propose a traceability assessment method that can derive high-resolution critical source areas (CSAs) of SIs by utilizing ambient air quality observations, global ozone (re)analysis data, and customized Lagrangian simulations. This approach enables us to facilitate a meticulous and systematic examination of the impact of direct and indirect Sis on tropospheric and near-surface ozone in six important sub-regions within the CEC during the spring and summer of 2019, as well as the unique circulations driving SIs, from a more refined and targeted tracing perspective. The findings reveal that impacts of indirect intrusions are more efficient at monthly scales, with contributions to tropospheric ozone reaching up to twice the magnitude of direct intrusions. The impacts of direct intrusions are more pronounced at daily scales, primarily occurring in May. In terms of contribution to near-surface ozone, the eastern plains frequently witness ozone exceedance events, with the most substantial impact from SIs observed, (e.g., contributing 15.8 % and 16.7 % to near-surface ozone in North China and East China, respectively), showcasing a remarkable ability to capture descending lower stratospheric air. In contrast, Loess Plateau and Central China, situated in central and western high-altitude regions, receive more intrusive ozone into the troposphere but exhibit minimal contributions to near-surface ozone. The indirect intrusions that generate the above impact come from 3 to 4 CSAs located thousands of kilometers away, evenly distributed latitudinally within the westerlies between 40° and 70° N (spaced 70 longitudes apart). These CSAs are intricately linked to the evolution of synoptic-scale Rossby waves, with Western Siberia identified as the most significant CSA. Conversely, the CSAs for direct intrusions are relatively concentrated, with those influencing the middle troposphere originating from the Tibetan Plateau and those influencing the lower troposphere predominantly located in Mongolia and central Russia, just a few hundred kilometers from the CEC. These sources are associated with typical atmospheric circulations such as the Northeast Cold Vortex and the South Asian High, where the intensity of the intrusion system plays a more crucial role than its frequency of occurrence. This study provides valuable insights for forecasting and mitigating the impact of SIs on ozone pollution in China and contributes to addressing the broader challenges posed by climate change.

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Kai Meng, Tianliang Zhao, Yongqing Bai, Le Cao, Ming Wu, Xuewei Hou, and Yuehan Luo

Status: open (until 14 Jun 2024)

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Kai Meng, Tianliang Zhao, Yongqing Bai, Le Cao, Ming Wu, Xuewei Hou, and Yuehan Luo
Kai Meng, Tianliang Zhao, Yongqing Bai, Le Cao, Ming Wu, Xuewei Hou, and Yuehan Luo


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Short summary
We studied the impact of stratospheric intrusions on tropospheric and near-surface ozone in Central and Eastern China from a stratospheric sources tracing perspective. SIs contribute the most in the eastern plains, with a contribution exceeding 15 %, while their contribution to the western and southern parts is small. Western Siberia and Mongolia are the most critical source areas for indirect and direct SIs respectively, with the Rossby wave and NECV being important driving circulation systems.