Impact of northward tropical cyclones on ozone in Southeastern China

Abstract. Autumn ozone pollution over Southeastern China (SEC) is usually influenced by tropical cyclones (TCs). Based on statistical analysis, WRF-CMAQ simulation, and TC vortex filtering method, this study explores the effects of the intensity and location of northward TCs on ozone in SEC. Results show that autumn maximum daily 8 h average ozone during 2014–2024 is strongly affected by northward TCs reaching typhoon (TY) intensity or above, especially within 120–130° E and 20–30° N. As TCs within this key subregion intensify to TY, SEC develops stronger subsidence, fewer clouds, stronger solar radiation, higher boundary layer height, lower relative humidity, weaker precipitation, and weaker surface winds, which jointly enhance ozone compared to other intensities. When TC intensity exceeds TY, the favorable meteorological conditions established at TY are no longer maintained, and ozone over SEC remains high but declines slightly, as confirmed by two simulations with intensifying TCs. In addition, comparison with the sensitivity experiment combining TC vortex removal with a weaker non-TC radiative regime revealed that the dynamical and radiative effects of northward TCs elevated ozone by over 10 ppb, with changes in biogenic emissions contributing approximately 1–3 ppb. Moreover, for TCs near 20° N, they primarily enhance ozone through photochemical production and horizontal transport, with impacts on southern SEC persisting even after landfall at 30° N. Finally, it is important to recognize the non-linear interaction between TCs and large-scale circulation such as the western Pacific subtropical high, which modulates TC tracks and intensity and subsequently influences ozone over SEC and even across the eastern China.