[Three-dimensional Structure Variation of PM_2.5 During Cold Front Advance in Eastern China]

Based on observational data and the WRF-Chem model, this study analyzed the large-scale air pollution in eastern China, which was caused by the weather process of a cold front moving southward, emphasizing the vertical structure of the boundary layer and the influence on the three-dimensional structure of PM_2.5. Our observations revealed that the heavy pollution near the surface was located at sparse or equal isobar in front of the cold front. During the process of the weather system moving in, the timing of the maximum PM_2.5 concentration at each station from north to south was delayed. The results show that the WRF-Chem model can better capture the spatial and temporal variations of surface and upper air meteorological elements and PM_2.5 concentrations over eastern China. The simulation results show that the boundary layer structure and the vertical profile of PM_2.5 at the same location of the mobile weather system showed similar characteristics. When the invasion takes place in a cold front, the pollutants in front of the cold front are rapidly lifted from the ground to a high altitude. The growth in PM_2.5 concentration and the increasing wind speed at high altitudes lead to the upward trend in PM_2.5 flux. As the altitude increases, the high-value area of PM_2.5 concentration tilts towards the warm air mass. The transit of the cold front at night led to more unstable convection within the boundary layer; the height of the boundary layer increased from north to south, reaching over 1 km, breaking the rules characteristic of the diurnal evolution of the boundary layer. The results indicate that the combination of vertical observations and elaborate simulation can effectively explain the impact of synoptic processes on the transport, distribution, and evolution of air pollution and provide precise pollution-control directives.