Decadal Shift of Teleconnections Intensifies Summertime High-Ozone Episodes in China

Summertime high-ozone pollution is a significant environmental concern for the North China Plain (NCP), affecting millions of residents. High-ozone episodes over the NCP often coincide with ridge formations, blocking the propagation of Rossby waves to the NCP, thereby creating favorable conditions for photochemical production of ozone. In recent years, more frequent ridge occurrences have intensified the emission-driven ozone problem over the NCP. We find that the climate factors driving the ridge formation have shifted over the decades. In the last two decades of the 20th century, wave trains induced by the low-latitude North Atlantic SST anomalies were the main driver of ridge frequencies. However, in more recent decades, the Eurasia teleconnection associated with Arctic sea ice variations over the Gakkel Ridge and warming anomalies in the central Indian Ocean had a greater influence. Based on CMIP6 projections, our study indicates that under the high-emission SSP5-8.5 scenario, the ridge frequency will likely increase, thereby amplifying meteorologically driven high-ozone pollution over the NCP.