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.