Impact of northward tropical cyclones on ozone in Southeastern China

Abstract. Ozone pollution in Southeastern China (SEC) during autumn are 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 the interannual fluctuations of autumn maximum daily 8 hour average ozone from 2014 to 2024 are mainly affected by northward TCs with intensities reaching typhoon (TY) or above level. As TCs intensify to TY, the photochemical activity, horizontal transport, and vertical mixing in SEC all develop to levels favorable for pollution, which jointly lead to higher ozone compared to other TC intensities. Although ozone remains high when TC intensity exceeds TY, further enhancement is inhibited by meteorological constraints, as evidenced by simulations of two severe ozone pollution episodes with intensifying TCs. In addition, comparing with the sensitivity experiment without TCs reveal that intense solar radiation combined with peripheral northerly winds during the northward TCs period elevated ozone by over 10 ppb, with changes in biogenic emissions contributing approximately 1~3 ppb. Moreover, when TCs are located near 20°N, they primarily enhance ozone through photochemical production and horizontal transport, with impacts on the southern SEC persisting even after TCs make 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 levels in the SEC and even across the eastern China.