The Impact of Stratosphere-to-Troposphere Transport Associated with the Northeast China Cold Vortex on Surface Ozone Concentrations in Eastern China

As the surface ozone (O3) 3 ) concentration is increasing despite emission control measures, it is urgent to clarify the impact of dynamic transport, such as quantifying the impact of stratosphere-to-troposphere transport (STT) on the surface O3 3 budget. Based on observations and numerical models, this study explores the relationship between the surface O3 3 concentration in eastern China (30 degrees-38 degrees N, 112 degrees-122 degrees E) degrees- 38 degrees N, 112 degrees- 122 degrees E) and the location and intensity of the Northeast China cold vortex (NCCV), a predictable weather system. The results show that when the NCCV occurs in the southeastern region (35 degrees-47.5 degrees N, 125 degrees-140 degrees E), degrees- 47.5 degrees N, 125 degrees- 140 degrees E), there is a corresponding increase in the surface O3 3 concentration in eastern China. The stronger the intensity of the NCCV is, the greater the increase in surface O3. 3 . The strongest 10% of the NCCV may cause an increase in the surface O3 3 concentration of 12-18 ppbv (30%-45% of the summer average surface O3 3 concentration). NCCV events and enhanced O3 3 are related to the STT. Anomalies in the 200-hPa wind fi eld induce downward motion in the NCCV region and its west side. The cold O3 3-rich stratospheric air is transported southeastward and downward during the NCCV period, leading to an increase in the surface O3 3 concentration. The correlation and predictability between 500-hPa meteorological fi elds and surface O3 3 concentrations are also highlighted in this work. SIGNIFICANCE STATEMENT: Despite the emission control measures taken in the past, the surface O3 3 concentration continues to increase in most regions of the world. It is urgent to quantify all the factors that impact the surface O3 3 concentration. This study focuses on a predictable weather system, the Northeast China cold vortex (NCCV), and its connection with stratosphere-to-troposphere transport (STT) that induces enhanced surface O3 3 concentrations. Our fi ndings provide a fresh perspective for studying the sources and forecasting of O3 3 concentrations by linking upper-level weather systems and meteorological fi elds with changes in surface O3 3 concentrations.