Associations of interannual variation in summer tropospheric ozone with the Western Pacific Subtropical High in China from 1999 to 2017

Associations between tropospheric ozone ( O 3 ) and climate variations have been extensively investigated worldwide. However, given the lack of historical O 3 monitoring data, the knowledge gaps regarding the influences of climate variations on long-term O 3 trends in China remain. The present study used a tropospheric O 3 dataset from the summers of 1999 to 2017 simulated by an atmospheric chemistry model to explore the linkage between summer O 3 and a dominant atmospheric circulation system - the Western Pacific Subtropical High (WPSH) pressure - on an interannual basis in China. During this period, both WPSH strength and O 3 concentrations in eastern and central China illustrated a growing trend. An EOF analysis was conducted to examine significant summer O 3 characteristics and patterns and their potential connections with the WPSH. We find that the correlation between the first principal component of summer ozone concentration in the EOF analysis and the WPSH reached 0.56 ( P <= 0.01 ) in China from 1999 to 2017. We show that the WPSH determines interannual fluctuations of summer O 3 , whereas O 3 precursor emissions contribute primarily to the O 3 long-term trend. Our results reveal that the WPSH plays a vital role in O 3 perturbation in the eastern seaboard regions and inland China. Precursor emissions made more significant contributions of up to 60 % to increasing O 3 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 O 3 occurred in the Yangtze River Delta (YRD), accounting for over 9 % to ozone perturbations from 1999 to 2017. We find that the effect of the WPSH on regional O 3 depends on the spatial proximity to the WPSH. We attributed the effects of the WPSH on O 3 interannual variations to the changes in air temperature, precipitation, and winds associated with the WPSH's intensity and positions.