长三角秋冬季典型区域霾天气特征及对比

为总结出霾天气发生时的相关影响因子、特征共性，选取长三角地区8个主要城市，2016~2019年秋冬季发生的7次典型霾天气过程，对比分析了3次霾天气过程中AQI、PM_2.5浓度、气象要素、天气形势、边界层特征的变化以及污染物来源.结果表明：不利的气象条件及高低空配置的静稳天气型导致霾天气的形成.3次过程AQI指数峰值分别为247、306及272，与PM_2.5浓度变化趋于一致.PM_2.5浓度和能见度呈明显负相关关系，且污染过程发生时能见度普遍偏低，2、3次过程能见度谷值均低于50m.高相对湿度、稳定的气温及静风与霾过程的形成有着紧密的联系.总体上混合层高度与AQI呈现负相关关系，混合层高度较低抑制垂直对流，从而使污染物在低空区域性积聚，3次污染过程混合层高度最低值均小于100m.逆温层的出现利于霾污染过程中污染物的累积，近地层的贴地逆温将污染物集聚在地表，第1次过程贴地逆温强度高达8.2℃；脱地逆温导致污染物在边界层内堆积并抑制其扩散，均易导致高浓度污染发生，第2次过程脱地逆温为主，强度高达4.8℃.气溶胶类型多为沙尘、大陆型污染物、污染型沙尘及烟粒.污染发生通常受局地排放、区域输送及长距离输送的共同影响，气团携带的因人为产生的细粒子也是造成污染的主要原因之一.

Characteristics and comparative of typical haze weather during autumn and winter in the Yangtze River Delta

To summarize the correlation influential factors, characteristics, and commonness under haze weather conditions, eight cities in the Yangtze River Delta and seven typical haze pollution processes were selected that occurred during the winter and autumn from 2016 to 2019. Based on the Air Quality Index (AQI) of the three most representative processes, PM_2.5 concentrations, meteorological factors, synoptic weather situation, atmospheric boundary layer characteristics, and pollution sources for the three haze processes were analyzed and found contrast with one another. The results showed that the unfavourable meteorological condition and the stagnant weather patterns due to the configuration of high and low altitude resulted in the formation of extreme haze condition. The peak values of the AQI in three representative processes were 247, 306 and 272, respectively, which were consistent with the change of PM_2.5 concentration. There was an obvious negative correlation between PM_2.5 concentration and visibility, the valley values of visibility were observed as low as 50m in the second and third haze processes. Generally, the pollution processes occur with low visibility. High relative humidity, stable temperature, and static wind were closely related to the formation of the haze process. In general, the AQI illustrated a negative correlation with mixed layer height. A lower mixed layer height affected the level of vertical convection of air contributed to the regional accumulation of substances at low altitude, and the minimum heights of the mixed layer in the three pollution processes were less than 100m. The inversion layer was conducive to high concentrations of pollution during haze pollution processes. On the one hand, the pollutants were trapped in the surface by the ground inversion layer, where the intensity of the ground inversion layer was up to 8.2℃ in the first process. On the other hand, the untouched ground inversion layer inhibited the vertical dispersion of pollutants in the atmospheric boundary layer; the second process was dominated by the untouched ground inversion for which the intensity reached to 4.8℃. Aerosol sources were mostly from the dust, polluted continental, polluted dust, and smoke. Air pollution was affected by the joint influence of local emission, regional transport, and long-range transport. The fine particles due to anthropogenic factors carried by the air mass were a major contributor to the pollution.