长江三角洲城市群霾的演变特征及影响因素研究

重建了长江三角洲1961~2007年霾气候数据序列,分析了霾日数的时空变化特征及城乡差异,并探讨了大气污染以及地面和近地层气象条件对霾发生的影响.结果表明,利用湿度—能见度指数参与霾气候序列重建的方法具有一定的合理性和科学性.过去47a间,长江三角洲霾日数总体上呈逐渐增多的趋势,并且四季霾日数都增加.空间上,整个长江三角洲霾日数基本上都呈增加趋势,并以杭州和南京增加最多.近30a来长江三角洲大城市、中等城市和城镇乡村站间霾日数变化具有明显差异.地面气象要素中风速和最长连续无降水日数与霾发生具有较好的对应关系.在霾天气过程和对应的清洁过程,近地层温度、位势高度和风场也都具有明显的差异.长江三角洲霾变化趋势与我国京津冀、珠江三角洲等地的变化一致.区域大气污染物排放量的增加,尤其是细颗粒物的增加是霾出现频率增加的可能原因,全球气候变化以及区域城市化造成的气象条件改变也有利于霾日的增加.

Characteristics and influencing factors of haze in the Yangtze River Delta region

The long-term hazy days from 1961 to 2007 were reconstructed and the spatial and temporal characteristics of the haze in the Yangtze River Delta (YRD) region were analyzed. The impacts of surface and near-surface meteorological conditions and air pollution on the haze occurrences were also considered using the methods of climate statistics, remote sensing and GIS analysis. The results indicated that the reconstructed hazy days with the consideration of humidity and visibility were fairly consistent with the measured records. From 1961 to 2007, the number of hazy days in the YRD region increased significantly, especially in Hangzhou and Nanjing. In the recent 30 years, the annual hazy days and their variations were different among large cities, medium-sized cities and towns and villages in the YRD region. Air pollution, surface wind speed and monthly longest consecutive dry days were closely correlated with the occurrence of hazy days in the YRD region. The removal processes of the occurrences of haze in the region were also influenced significantly by near-surface temperature, geo-potential height and wind field. The variation trends of hazy days in the YRD region were consistent with those in Beijing-Tianjin-Hebei region and Pearl River Delta. The possible reason of increasing hazy days was the increasing emissions of air pollutants, especially the increase of fine particles. The changed meteorological conditions caused by global climate change and regional urbanization were also the reasons of the increasing hazy days.