Impact of the strong wintertime East Asian trough on the concurrent PM2.5 and surface O3 in eastern China

Abstract

The East Asian trough (EAT) is often regarded as an important controlling factor for the East Asian climate. However, there has been no detailed study of its effects on compound pollutants including PM2.5 and O3. This study investigates the possible effect of the intraseasonal EAT events on PM2.5 and O3 concentrations over eastern China in early winter (November–January). Studies show that 65% of the strong EAT evolved from a cyclonic anomaly over Kazakhstan have significant effects on PM2.5 concentration in the North China Plain. From day −3 to day 0 prior the EAT peak, increased northerly wind and higher planetary boundary layer height caused by the strong EAT enhance atmospheric diffusion conditions, leading to lower PM2.5 concentration. PM2.5 concentration tends to decrease on day 4 prior to the peak of EAT events and reaches its minimum on the third day after that. In addition, surface O3 concentrations in the Yangtze River basin experienced the first decrease and then increase with a turning point at day 1 after the peak of EAT events. These changes in the O3 concentration are attributed to changes in the surface temperature anomaly and surface downward solar radiation associated with the EAT. Specifically, the EAT-related lower surface temperatures and less downward solar radiation before the peak of the EAT events (i.e., day −4 to day 1) favor lower O3 concentrations and vice versa after the peak of the EAT (i.e., day 2 to day 4). Our findings could be of great value for the targeted emission reductions in eastern China in early winter.