Systematic classification of circulation patterns and integrated analysis of their effects on different ozone pollution levels in the Yangtze River Delta Region, China

Abstract

Abstract Ozone pollution is of great concern in the Yangtze River Delta (YRD) region of China. The regional air pollution is significantly associated with dominant weather systems. In this study, the relationship between O3 concentration and weather patterns over the YRD region is investigated. Specifically, based on the National Center for Environmental Prediction reanalysis data and the sums-of-squares technique, six typical weather patterns in 2017 are identified. It is found that higher O3 concentrations tend to occur under the weather patterns 3, 4 and 5. These high mean O3 concentrations are associated with the southerly flow introduced by the western Pacific subtropical high, the low pressure in the saddle field and the warm ocean current introduced by typhoon. Whereas the low mean O3 concentrations under the weather patterns 1, 2 and 6 are linked to the northwesterly flow brought from the Siberian high. Moreover, when the light pollution appears, main synoptic weather systems get weakened and the wind speed is reduced at 850 hPa and surface. At the same time, the temperature increases due to the weakening of the northerly wind introduced by the Siberian high and the North China warm high, and the strengthening of the southerly wind introduced by a southwest vortex. The occurrence of the heavy pollution is highly related to these further enhanced synoptic processes. The downward motion is obviously enhanced due to the trough or ridge deepening at 500 hPa and the strong downdraft around the typhoon. Higher temperature, lower wind and stronger downward motion due to the minor changes of atmospheric circulation establish conditions conducive to the formation and accumulation of O3.