黑河地区沙漠气溶胶浓度和谱分布特征

CHARACTERISTICS OF THE CONCENTRATION AND SIZE DISTRIBUTION OF DESERT AEROSOL OVER HEIHE REGION

本文根据黑河地区的观测结果,着重分析了沙漠气溶胶浓度及其谱分布特征。沙漠气溶胶浓度较低,其中细粒子占绝对优势。扬尘时气溶胶浓度显著增加,其中粗粒子增加幅度最大,比平时高20倍以上,直径(D)在2.0—100 μm间的粗粒子浓度比重从晴天的1.9％上升到9.6％。中等降雨对D>4.0μm的沙漠气溶胶粒子的清除效率非常高(>90％),但对总浓度的清除效果不很明显(42.5％),尤其是对其中的D<O.4μm的小粒子(32.8％),因此0.5<D<4.0μm的沙漠气溶胶粒子具有远距离输送的能力。大尺度气团的迁移大大改变了气溶胶浓度。背景沙漠气溶胶浓度的日变化主要由大气扩散稀释能力控制。背景沙漠气溶胶有三种来源:全球背景气溶胶、地区性的背景土壤尘和局地土壤尘。实测粒度谱呈三峰型结构,能用三对数正态分布函数和来拟合。

Concentration of desert aerosol is usually low, in which fine particles are predominant, striking increase of dust concentration is observed during blowing dust periods, particularly that of coarse particles, which increases by more than 20 times than that on fine days, and the number of particles with diameter(D) between 2.0 and 10.0/μm accounts 9.6% of total number of particles, much higher than that on clear days(1.9%). Moderate precipitation removal is the most effective to desert particles with D> 4.0/μm(90% ), but not so effective to all particles, specially to those with D< 0.4/μm.Therefore desert aerosols with 0.5 < D<4.0μm may be transported long-distance. Movement of large-scale air mass may greatly change the concentration of desert aerosol. The diurnal variation of concentration of background desert aerosol is mainly controlled by air disperse dilution. There are three sources of background desert aerosol: global background aerosol, large range background dust and local soil dust. The measured size distribution of desert aerosol are characterized by 3-modes, which can be fitted very well by the sum of three log-normal distribution functions.