Chemical characteristics of water-insoluble components in aeolian dust collected in China in spring 2002

Abstract

Aeolian dust collected at three stations in China (Beijing, Qingdao, and Hefei) in spring 2002 has been analyzed and their chemical features have been thoroughly discussed. The mass concentrations of aeolian dust collected were high in coarse grains, and the distribution patterns against particle size were different among the sampling stations. When large-scale dust events were observed, the concentrations of suspended particle with a particle size over 2 μm especially increased. The chemical compositions (Al2O3 Na2O, P2O5, Total Fe2O3, Rb, Zr, and La) of all but one aeolian dust sample were almost constant in coarse grains and quickly decreased below 1.1-2.1 μm. This result suggests that the contribution of mineral aerosol to aeolian dust sharply decreased in fine grains. In the dust event of March at Beijing, however, these elemental concentrations were almost constant over the variations of particle size. This fact indicates that the large-scale dust event supplied a large amount of mineral aerosol even in fine grains. The elemental concentration ratios to Al2O3 were almost constant in coarse-medium grains, but suddenly increased below 1-2μm: the mineralogical composition was homogenous in coarse-middle grains, but changed in fine grains. The grain-size distribution pattern of the elemental concentration ratio has no systematic variations with or without a dust event or among three sampling stations. Therefore, chemical features of aeolian dust coming from inland China and suspended particle accumulated around sampling locations are very similar. On the contrary, some heavy elements (Cr, Ni, Cu, Zn, Mo, Cd, Sb, Sn, Pb, and Bi) had different features from elements that originated form mineral aerosol such as Al2O3. The concentrations and metal/Al2O3 ratios for these heavy metals increased with decreasing particle size. For example, the Cu/Al2O3 and Pb/Al2O3 ratios dramatically increased tenfold to hundredfold with decreasing particle size. These distribution patterns against the particle size suggest that anthropogenic materials were contaminated to finer grains.