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

Abstract

Abstract As the surface ozone (O3) 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 budget. Based on observations and numerical models, this study explores the relationship between the surface O3 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 O3 concentration in eastern China. The stronger the intensity of the NCCV is, the greater the increase in surface O3. The strongest 10% of the NCCV may cause an increase in the surface O3 concentration of 12–18 ppbv (30%–45% of the summer average surface O3 concentration). NCCV events and enhanced O3 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 O3-rich stratospheric air is transported southeastward and downward during the NCCV period, leading to an increase in the surface O3 concentration. The correlation and predictability between 500-hPa meteorological fields and surface O3 concentrations are also highlighted in this work. Significance Statement Despite the emission control measures taken in the past, the surface O3 concentration continues to increase in most regions of the world. It is urgent to quantify all the factors that impact the surface O3 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 concentrations. Our findings provide a fresh perspective for studying the sources and forecasting of O3 concentrations by linking upper-level weather systems and meteorological fields with changes in surface O3 concentrations.