一次冷锋过程中我国区域空气污染边界层特征

利用常规地面气象和探空资料、ERA-interim再分析资料、以及全国PM_2.5浓度数据，针对2015年3月7~11日一次冷空气南下的锋面天气过程中，我国华北、华东地区出现的大范围空气污染，开展了高空各层天气形势分析，以及本次过程中污染区域由北至南6个城市（北京、章丘、郑州、南阳、武汉、长沙）边界层气象要素的垂直结构及其时空演变特征的研究.结果表明：在污染前期（3月7~8日）中高纬度500hPa平直的纬向环流和地面均压场，为污染天气的发生和维持以及空气污染物的集聚提供了有利的环流场.污染中期（3月8~10日）冷空气南下，地面冷高压向华东地区移动，重污染区域随冷高压前部的弱低压场或均压场由北向南移动.伴随着天气系统移动，六个地面观测站的边界层特征在时空上表现出相似性，由北向南各站在污染期间先后出现多层逆温，风速较小，逆温层下相对湿度较大.此次多层逆温的形成是由于夜间近地面辐射冷却、冷锋移动过程中产生的锋面逆温以及边界层以上的下沉运动造成的.本研究揭示了在天气系统移动中，位于天气系统相同部位站点的边界层结构具有共同的特征，及其与空气污染的关系.

Boundary layer characteristics of an air pollution event in China during a cold front

Using radiosonde and weather station data, reanalysis data of ERA-interim, and national PM_2.5 concentration data, a cold front process during March 7 to 11, 2015 and its impact on air pollution were discussed. Our research focused on the circulation features at different levels of air, the vertical structure of the meteorological factors in the boundary layer and its spatiotemporal evolution characteristics from the north to south at six sites (Beijing, Zhangqiu, Zhengzhou, Nanyang, Wuhan, Changsha) during the southward moving process of the cold front. The results showed that in the first stage of the air pollution event (7~8March), the zonal circulation at 500hPa and the surface pressure field were even, and generated favorable conditions for the accumulation of air pollutants. In the second stage of the event (8~10March), the regions with heavy pollution were generally located in front of the cold high with weak pressure gradient, and moving southward accompanying the southward movement of the cold front. With the passing of the weather system, the boundary layer characteristics at six sites showed a similar feature of multi-level inversion occurring sequentially in time, and from north to south in space. The wind speed was low, and the relative humidity was high within the inversion layer. The formation of this multi-level inversions was due to the near-surface radiation cooling at night, frontal inversion of the moving cold front, and air sinking above the boundary layer. This study revealed that in a moving weather system, the boundary layer structures in the same part of the weather system had common characteristics, which were related closely to the occurring of air pollution.