Based on visibility, relative humidity, weather phenomenon and related other data in Nanjing during 1980-2008 ,by using percentile, grades and Ridit analysises, study is performed of the characteristics of visibility caused by only air pollution, excluding meteorological effects. Results show that both the yearly and seasonal visibilities have declined notably over the past 29 a. The trend of "bad" or "common" visibility goes up, "good" visibility trend declines, and the four seasons'visibility and their distribution are characterized by that in spring(fall) visibilty change is remarkably different from that in summer( winter), in addition, the visibility is declining with decades and the visibility difference between seasons is also diminished. Furthermore, the visibility of winter becomes worse and worse since 1987,and in this century the visibilty in winter is mainly "bad" and "common", and in the other seasons it is mainly "common".%利用南京国家气候基准站1980-2008年能见度、相对湿度和天气现象等气象要素资料,剔除气象因素对能见度影响,采用百分位分析法、等级分析法和Ridit分析法,分析了由于空气污染造成南京地区大气能见度的变化趋势.结果表明,近30 a来,南京市年平均和四季大气能见度整体显著下降,但其中"较差"和"一般"能见度出现频率显著上升,"较好"能见度则明显下降;四季能见度及其分布均呈现春、夏季节变化不同,秋、冬季节变化显著的特点;能见度呈逐年代降低但降幅减缓;能见度季节差异也呈逐年代减小趋势;此外,冬季能见度早在1987年起变差;并且本世纪以来,冬季能见度以"较差"和"一般"为主,其余三季均是以"一般"为主.
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