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

Abstract As the surface ozone (O 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 O 3 budget. Based on observations and numerical models, this study explores the relationship between the surface O 3 concentration in eastern China (30°–38°N, 112°–122°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°–47.5°N, 125°–140°E), there is a corresponding increase in the surface O 3 concentration in eastern China. The stronger the intensity of the NCCV is, the greater the increase in surface O 3 . The strongest 10% of the NCCV may cause an increase in the surface O 3 concentration of 12–18 ppbv (30%–45% of the summer average surface O 3 concentration). NCCV events and enhanced O 3 are related to the STT. Anomalies in the 200-hPa wind field induce downward motion in the NCCV region and its west side. The cold O 3 -rich stratospheric air is transported southeastward and downward during the NCCV period, leading to an increase in the surface O 3 concentration. The correlation and predictability between 500-hPa meteorological fields and surface O 3 concentrations are also highlighted in this work. Significance Statement Despite the emission control measures taken in the past, the surface O 3 concentration continues to increase in most regions of the world. It is urgent to quantify all the factors that impact the surface O 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 O 3 concentrations. Our findings provide a fresh perspective for studying the sources and forecasting of O 3 concentrations by linking upper-level weather systems and meteorological fields with changes in surface O 3 concentrations.