兰州市尘暴过程中降尘粒度特征探析

通过对兰州市两次强度上有较大差异的尘暴样的采集、粒度分析及其与自然降尘样的对比研究,揭示出兰州市尘暴降尘粒度特性的一些细微特征。不论是自然降尘样还是尘暴样,皆以4～63μm的粉砂为主,说明粉砂粒级的颗粒是兰州地区自然降尘与沙尘暴所携带的主要组分;虽然含量甚微,但是尘暴样中存在近源低空气流所搬运的粒径(181.97～724.44μm)较大的粗颗粒物质。在粒径-体积百分含量曲线上,尘暴样基本上为三峰分布模式,区别于自然降尘样的双峰模式。同时,尘暴样具有向粗、细颗粒区间(尤其是细颗粒区间)延伸并富集的特点,尘暴强度越大,其延伸富集的程度也越明显,而且,随着尘暴强度的增大,其主峰的众数粒径呈减小趋势。

Analysis of dust grain-size characteristics of two dust storm events in Lanzhou

We collected the dust samples of two dust storms in Lanzhou between which there was great difference in intensity,and analyzed their grain-size,then compared them with the natural dust sample. The result revealed that the dust storm in Lanzhou had some minute characteristics on the grain-size. Whether the natural dust sample or the dust storm sample,both of them had a main component of the silt sand whose grain-size was 4 ～ 63μm. And it showed that dust with its grain-size at the level of silt sand is the major component of the natural dust and dust storm in Lanzhou. In the dust storm samples,there was also much coarser particles with grain-size of 181. 97 ～ 724. 44μm,which was mainly transported by air current nearing ground and from nearby area,although its content was low. The grain - size distribution pattern of the dust storm samples was three - peak states,which was different from the one with two - peak states of the natural dust sample. The characteristics of the dust storm samples were: 1) the samples had much dust with rough and fine grain - size,especially fine grain - size,the stronger the dust storm was,the more obvious the trend was; 2) with the intensity of dust storm increasing,the model of the main peak in its grain - size distribution pattern became smaller.