Associations of interannual variation of Summer Tropospheric Ozone with Western Pacific Subtropical High in China from 1999 to 2017.

Associations between tropospheric ozone (O₃) and climate variations have been extensively investigated worldwide. However, given the lack of historical O₃ monitoring data, the knowledge gaps regarding the influences of climate variations on long-term O₃ trends in China remain. The present study used a unique tropospheric O₃ dataset from the summer of 1999 to 2017 simulated by an atmospheric chemistry model to explore the linkage between summer O₃ and a dominant atmospheric circulation system – the Western Pacific Subtropical High Pressure (WPSH) on an interannual basis in China. During this period, both WPSH strength and O₃ concentrations in eastern and central China illustrated a growing trend. An EOF analysis was conducted to examine significant summer O₃ characteristics and patterns and their potential connections with the WPSH. We show that the WPSH determines interannual fluctuations of summer O₃, whereas O₃ precursor emissions contribute primarily to the O₃ long-term trend. Special efforts were made to discern the associations of O₃ variations in major urban agglomerations of China and the WPSH. The results reveal that the WPSH plays a more vital role in O₃ perturbation in the eastern seaboard regions and inland China, but leads to lower O₃ levels in the Pearl River Delta (PRD) region. Precursor emissions made more significant contributions up to 60 % to increasing O₃ trends in the inland urban agglomerations than coastal regions in eastern and southern China. The strongest contribution of meteorological conditions associated with the WPSH to summer ozone concentration occurred in the Yangtze River Delta (YRD), accounting for over 9 % to ozone perturbations from 1999 to 2017. Overall, we find that the effect of the WPSH on regional O₃ depends on the spatial proximity to the WPSH. We attributed the effects of the WPSH on O₃ interannual variations to the changes in air temperature, precipitation, and winds associated with the WPSH's intensity and positions. [ABSTRACT FROM AUTHOR]