初冬一次冷锋输送过程对中国东部霾天气的影响

利用常规地面气象资料、NCEP/NCAR再分析资料以及全国PM_2.5浓度数据，并结合后向轨迹、空气污染输送指数和传输通量分析，针对2019年12月10~11日一次冷锋输送造成我国中东部地区出现的大范围霾天气过程进行了分析.结果表明：（1）霾期间高空500hPa以经向环流为主，伴随着高空低压槽引导地面冷锋向东南方向移动，污染物浓度大值区也依次由华北地区移至黄淮、江淮地区.（2）冷锋过境前，华北至长江三角洲区域PM_2.5浓度均有明显增涨；北京以偏南方向的污染物输入为主，济南以西北和偏东方向输入为主，南京则主要是偏北和偏西方向的输入.（3）冷锋过境时，冷空气迅速将北京站的污染物清除；而济南站则受高压底部偏东风回流的影响，PM_2.5浓度维持在50μg/m³左右；冷锋推进至南京站时西北风已较小，对污染物的清除作用不明显.以江苏省为例，整个过程中，江苏本地污染物贡献占25.8%，江苏以外的污染物贡献占74.2%，以输送为主.（4）冷锋过境后，3站的边界层结构也略有不同，北京站的逆温层迅速被打破；济南站由于受海上暖湿平流影响，近地面由等温层变成逆温层；而南京站的近地面则由逆温层变为等温层.本研究揭示了在冷锋南下过程中，上游污染物对下游地区的影响，以及南北方站点表现出不同的污染物变化和清除特征.

Impact of a cold front transport process on haze weather in eastern China in early winter

Regular surface observation meteorological data, NCEP/NCAR reanalysis data, and national PM_2.5 concentration data, combined with backward trajectory, air pollution transport index, and transport flux analysis, were used to analyze a cold-front induced large-scale haze weather process during December 10 and 11, 2019 in central and eastern China. The results showed that:(1) During the haze period, 500hPa was dominated by the meridional circulation, and accompanied with the upper-air low-pressure trough leading the ground cold front to move to the southeast. The heavy polluted area also moved from North China to Huang-huai and Jiang-huai. (2) Before the cold front passage, PM_2.5 concentration in the region from North China to Yangtze River Delta increased significantly. Beijing was dominated by pollutants imported from the south, Jinan was mainly affected by pollutants from the northwest and east, and PM_2.5 in Nanjing was mainly influenced by pollutants from north and west. (3) When the cold front passed through, the cold air quickly removed pollutants over Beijing Station, while the Jinan station was affected by the backflow of easterly wind at the bottom of the high pressure, and the PM_2.5 concentration was maintained at about 50μg/m³. When the cold front intruded into the Nanjing station, weakened northwest flow had little effect on the removal of pollutants. Taking Jiangsu province as an example. In the whole cold front process, the contribution of local pollutants accounted for 25.8%, and the contribution of pollutants outside Jiangsu accounted for 74.2%, which were mainly transported from North China. (4) After the passage of the cold front, the boundary layer structures over the three stations were slightly different from each other. The inversion layer over the Beijing station was quickly dissipated, the lower boundary layer over the Jinan station changed from the isothermal layer to the inversion layer due to the influence of warm and wet advection from the sea, and the near-surface boundary layer over the Nanjing station changed from the inversion layer to the isothermal layer. This study revealed the impact of upstream pollutants on downstream area during the southward movement of the cold front, as well as the different evolution and removal characteristics of PM_2.5 at the stations in the north and south China.