北京地区气溶胶光学厚度中长期变化特征

利用1977～1985年北京地区太阳直接辐射谱资料，分析获得了气溶胶光学厚度谱特性，使用PIS光谱仪从1993年3月到1995年3月，持续观测了北京地区晴天和少云天气的太阳直射光谱。得到了至今较为长期系统的城市大气气溶胶光学性能及特征。研究表明:（1）气溶胶光学厚度有春夏季大，秋冬季小的统计规律；（2）能见度分级后，同一能见度下气溶胶光学厚度各季节之间的差别大为减小，地面能见度对整层光学厚度表现出了较强的约束作用，文中给出了统计关系；（3）气溶胶光学厚度有逐年增高的趋势，1977年至1994年间增长了约三分之二。

The Mid-Long Term Features of Atmospheric Aerosol Optical Depths over Beijing Area

The speCtral optical depths of atmospheric aerosols in the urban area of Beting are deduced from the direct solar radiation data from 1977 to 1985.In addition,the successive high speCtralresolution observations of the radiation with a PIS spectrometer are conducted from March 1993 toMarch 1995 under clear and partly cloudy conditions in the same area. The features of aerosol opticalproperties are described for an unprecedented long period. The results show that(1) aerosol opticaldepths (AOD) are thick in spring-summer, and thin in autumn-winter;(2) with the classification of thesurfaCe visibility the seasonal difference of the AOD is greatly reduced for the same kind of visibility,and the amplitude of the AOD is limited by the visibility; (3) there is a tendency of year by year increaseof the AOD, and on the yearly averaged basis the AOD in 1994 has increased by two thirds of that in1977.