Mineralogical characteristics of soil dust from source regions in northern China

Mineral compositions of aerosol particles were investigated at four sites (Aksu, Dunhuang, Zhenbeitai, and Tongliao) in desert regions of northern China from March to May in 2001 and 2002 during the intensive field campaign period of ACE-Asia (Aerosol Characterization Experiments-Asia). The X-ray diffraction (XRD) results show the main minerals for Asian dust are illite, chlorite, kaolinite, quartz, feldspar, calcite, and dolomite. Gypsum, hornblende, and halite are also detected in several samples. Semi-quantitative mineralogical data of aerosol samples show that carbonate content decreases from western to eastern source areas; that is, soil dust collected at western source area sites of Dunhuang and Aksu are enriched with carbonate, while northeastern source area site of Tongliao is associated with low carbonate content. But the spatial distribution of feldspar exhibits a different pattern as compared to carbonate, increasing from the western to the eastern sources. The total clay content is significantly higher (73% in average) at the deposition site of Changwu than those at source areas. Air-mass back trajectory studies for the three dust storm events observed at Changwu, showed that soil dust transport pathways were as expected from carbonate content for the source identification, further demonstrating that carbonate was a useful tracer for eolian dust on regional scale in northern China.