Anomalous surface O3 changes in North China Plain during the northwestward movement of a landing typhoon

As high impact weather in a large scale, typhoon movement from the northwest Pacific into inland regions influencing ambient O3 changes is unclear, especially in North China Plain (NCP). A landing Typhoon Ampil during July 17-24, 2018 was studied herein to characterize the surface O3 anomalies during its movement over NCP. Landing typhoons present large negative O3 anomalies at the center of the typhoon and positive O3 anomalies 600-1700 km away from the center. During the northwest movement of Typhoon Ampil to the NCP, the area and magnitude of both positive and negative O3 anomalies shrank, particularly in the western and northern periphery, where the typical diurnal change of O3 dissipated with nocturnal O3 enhancement in the NCP. The spatiotemporal patterns of surface O3 anomalies in the NCP were induced significantly during various stages of typhoon movement with a stable structure in the atmospheric boundary layer, strong solar radiation on sunny days, and stratosphere-to-troposphere transport (STT) in the typhoon periphery, depending on the changing intensity, distance, and orientation of the typhoon center. Among them, the STT played a considerable role and contributed 32% to the positive anomalies of surface O3 in the NCP. Under the influence of westerly jets and high pressure at mid-latitudes on the typhoon movement, strong wind convergences in the upper troposphere were formed intensifying the downdraft of O3-rich stratospheric air to the boundary layer in the NCP with an asymmetrical distribution of surface positive O3 anomalies over the periphery of typhoon. This study could improve our understanding of regional ozone changes with meteorological influences.