哈尔滨市特大沙尘暴沉降物的粒度分布及意义

Grain-size distribution of fall-outs of an exceedingly large dust storm in Harbin City and its implications

对2002年3月20日中国黑龙江省哈尔滨市遭遇的特大沙尘天气沙尘沉降物进行的粒度分析表明,沙尘沉降物属粉质亚砂土,以4～63μm的粉砂为主,占71.18%,>63μm的砂粒组分占21.7%,<4μm的粘土组分含量最少,仅占7.13%。粒度为三峰态分布,29.2～34.7μm粒级的粗粉砂形成第一主峰,含量约占7.4%,420.5～500μm粒级的中砂组分形成第二主峰,含量约占1.29%,而0.69～0.82μm粒级的细粘土组分形成第三主峰,含量约占0.52%。平均粒径Mz为28.4μm,分选系数为1.81,偏态为0.044,峰态为1.494,粉粘比为7.3。粒度分布显示这次哈尔滨市沙尘沉降物是迄今为止国内有见报道中最粗的,沉降物是不同来源沙尘远距离和近距离搬运的混合体,粗颗粒为低空气流搬运的近源物质。哈尔滨市或周缘邻近区域是这次特大沙尘暴的降尘中心,属大气动力条件较强的中心或近中心地带。哈尔滨城市扩展区域的疏松地表裸土、河床及漫滩细粒冲积物以及市内地表建筑沙土等都可以是哈尔滨市沙尘沉降物的主要物源。因此哈尔滨地区防治沙尘暴工作的重点应放在哈尔滨市周边沙尘源区的治理上。

Grain-size analysis was performed on sand and dust fall-outs of an exceedingly large dust storm that occurred in Harbin, Heilongjiang Province, on March 20, 2002. The results indicate that sand and dust fall-outs are silty sandy loam. The silt-sized （4 - 63μm） fraction predominates, making up 71.18%; the sand-sized fraction （〉63μm） accounts for 21.7% and the clay-sized （〈4μm） fraction is scarce, accounting for only 7.13%. The grains are of trimodal distribution： the coarse silt-sized （29.2 - 34.7 μm） fraction forms the first main peak, making up -7.4%; the medium sand-sized （420.5 - 500μm） fraction forms the second main peak, accounting for -1.29%; and the clay-sized （0.69 -0.82 μm） forms the third main peak, accounting for -0.52%. The mean grain diameter Mz is 28.4 μm, with a sorting coefficient of 1.81, a skewness of 0.044, a kurtosis of 1.494 and a silt/clay ratio of 7.3. The grain-size distribution shows that sand-dust fall-outs in Harbin are the coarsest ones reported ever since in China. The fall-outs were a mixture of sands and dusts derived from different sources and transported over long and short distances, and coarse particles were near-sources materials that were transported by low-altitude airflow. Harbin and its peripheral areas should be the dust fall-out center of this exceeding large dust storm and belong to the center or near-central zone with relatively strong atmospheric dynamic conditions. Nude loose soils, river beds and floodplain fine alluvium, sand-dust of city construction sites and so on in the urban expansion areas of Harbin may all be main material sources of sand and dust fall-outs of Harbin. The focus of the work for preventing sand-dust storms in Harbin should be on controlling sand-dust source areas at the peripheries of Harbin.