ABSTRACT

Variations of the chemical composition and elemental speciation of aeolian dust transported from China to Japan were investigated in this study. During 6-12 April 2002, a large-scale dust event was observed in China, Korea, and Japan. Aerosol samples collected in Beijing, Fukuoka, Nagoya, and Tsukuba at that time were used for this study. Variations of most elemental concentrations against the particle size showed similar trends to that of Al concentration. The particle size distributions indicate that myriad elements in the aerosols originated mainly from mineral aerosols. The metal/Al concentration ratios showed little difference in chemical compositions for aerosols sampled at Beijing and Japanese stations: the chemical composition of aeolian dust is conserved during transportation. Examination by X-ray absorption near-edge structure (XANES) spectroscopy revealed that the Fe(III)/Total Fe (T-Fe) ratios of the aerosols collected in Beijing and Fukuoka were mutually resemblant, indicating that the oxidation-reduction reaction of Fe in aeolian dust during its transportation is negligible. However, their ratios were much higher than those of China loess and simulated Asian mineral dust (Chinese geo-reference materials: CJ-1 and CJ-2). Because the aerosol grain size is much smaller than those of CJ-1 and CJ-2, the fine mineral was transported selectively by wind from top soils. It was easily oxidized and had a high Fe(III)/T-Fe ratio. The XANES spectra of Mn in the aerosol indicated that the Mn(III)/Total Mn (T-Mn) ratios of the aerosol collected in Fukuoka were smaller than those of the dust collected in Beijing. The ratios of the aerosols in Beijing resembled those of CJ-1 and CJ-2. Moreover, only medium grains of the aerosol in Fukuoka had high Mn(III). The other grains had an almost identical Mn(III)/T-Mn ratio as the aerosol collected in Fukuoka in the no event. Thereby, most medium grain aerosols collected in Fukuoka comprised aeolian dust coming from China with high Mn(III)/T-Mn ratios like those of CJ-1 and CJ-2, but the other grain aerosols mixed greatly with local aerosols having low Mn(III)/T-Mn ratios. On the other hand, some elements such as Zn and Pb had different Al concentration ratios from Mn and Fe. The Zn/Al and Pb/Al concentration ratios of fine grains increased tenfold to a hundredfold with the decrease of particle size. Therefore, the increasing trend for these elements indicates that the fraction of anthropogenic materials was greatly increased in fine grains. The XANES spectra of Zn suggested that the contribution of mineral aerosols decreased gradually with decreasing particle size and that the residual components were explained by Zn(NO₃)₂ in coarse-medium grains and ZnSO₄ in fine grains. However, Zn in aeolian dust, which is a main component of mineral aerosols, only rarely originated from anthropogenic materials when a large-scale dust event was observed.