兰州市沙尘和非沙尘天气降尘的粒度特征比较

Comparison of Particle Size between Aeolian Dusts Collected under Dust Event and Non-dust Event

选择兰州市典型沙尘天气和非沙尘天气收集两类降尘,并对其进行粒度测定。结果表明:两种类型降尘粒度特征差别明显。总体上看沙尘天气和非沙尘天气降尘都以粉砂为主,但沙尘天气降尘粒度比非沙尘天气降尘偏粗,分选更差。非沙尘天气降尘粒度频率曲线呈双峰态分布。而沙尘天气降尘则呈单峰正偏态分布特征,说明沙尘天气沉降物来源比较单一。沙尘天气和非沙尘天气降尘的粒度分布曲线与兰州黄土的十分相似,说明现代降尘是地质时代风尘活动的继续,现代风积作用仍在进行。而它们粒度参数之间的差异可能与降尘堆积物的粘土化过程有关。

The dustfall samples collected under typical dust and non-dust weather were made particle size analysis in Lanzhou. The results showed that there are many differences between two samples. In general, two types of dustfall are mainly composed of silt, but the dustfall collected under dust weather is poor sorting and more courser than that under non-dust weather. Frequency curve of aeolian dusts under dust and non-dust weather exhibit bimodal and positively biased distributions, respectively, which showed that the source of aeolian dust under dust weather was relatively single. The distributions of particles size of two samples are largely similar with that of Lanzhou loess, which shows that modern aeolian sedimentary process continues from geological history and modem dust accumulation has ingenerated relationship with the ancient sediment, however, the differences of grain size parameters between aeolian dusts under dust and non-dust weather and Lanzhou loess are probably in relation with argillation process of aeolian dust.