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Aerosol samples, which are dust suspended in the atmosphere, were collected in Qira, Aksu, and Shapotou in 2001 and Qira, Dunhuang and Shapotou in 2002, which are located between north-western and central China, one of the possible source areas of Asian dust. Their chemical and isotopic compositions, mainly Sr and Nd isotopic compositions, in the total suspended particles (TSP) and finer fraction (ψ < 5 μm) in the TSP were analysed. There is a slight difference in the chemical compositions of TSP and the ψ < 5 μm fraction that can probably be attributed to the relative increase of silt and/or clay in the ψ < 5 μm fraction. 87Sr/86Sr ratios were 0.71770-0.72030 in the TSP and 0.72349-0.72737 in the ψ < 5 μm fraction over all sampling sites, although eNd(0) values were relatively constant, from −11.3 to −9.3. The isotopic characteristics due to the variation of particle size are clearly seen in Rb-Sr and Sr-Nd isotopic correlation diagrams, which are usefu1 aids to identify the sources of Asian dust. In addition to the possible isotopic change with particle size, results of Sr and Nd isotopic measurements suggest that the broad area from the north-western to the central part of China, i.e. from the Taklimakan Desert to the Central Loess Plateau, is characterized as a single possible source component of Asian dust. Clarifying the correlation between geochemical features and particle size is an important requirement that may allow the correlation of long-range transported Asian dust to possible source materials.

Aerosol sampling and meteorological observations were carried out from March 2001 to April 2004 at Aksu, in the northern part of the Taklimakan Desert in north-west China. There were three intensive observation periods (IOP): 11-24 April 2002, 16-26 March 2003 and 10-17 March 2004.The observed maximum concentration of total suspended particles (TSP) was 5.2 mg m−3 during the dust event of April 2003. Variations in the TSP and PM11 (panicles smaller than 11 μm) show that high atmospheric concentrations were observed during dust events that occurred mainly in spring and summer. According to the meteorological observations, dust storms or blowing sandldust occurred not only in spring, but also in summer and autumn, though floating dust occurred mainly in March and Apri1. The frequency of dust events was consisted with the results of dry deposition.During spring and summer, the size-distribution of aerosols is unimodal with a maximum in the range 3.3-7.0 μm, while in winter the size-distribution shows a bimodal pattern with two peaks; at 3.3-7.0 μm for soil particles and 0.65-1.1 μm for anthropogenic panicles. From the results of size distribution of soluble ion concentration, anthropogenic particles consist mainly of ammonium sulfate and ammonium nitrate, which result from coal combustion for heating during winter.Concerning chemical composition, aerosols from Aksu contain a significant amount of evaporate minerals such as calcium carbonate (calcite), sodium chloride (halite), and calcium sulfate (gypsum and anhydrite). These evaporates are common minerals in the saline soils which are widespread around observation site, and it is suggested that they are provided into atmosphere from the ground surface together with soil particles.Major element composition for aerosols in Aksu show a lower SiO2 content and higher FeO, K2O and MgO content compared with that for the saline soils (ψ < 125 μm), the loess deposits in the Tarim Basin and Central Loess Plateau, and Taklimakan Desert sands (ψ < 125 μm). This suggests that minerals rich in Fe, K and Mg, such as clay minerals and mica, come selectively from the soil surface into the atmosphere as mineral aerosols. This is because their particle size is generally smaller than that of quartz, the main constituent minerals in the soil.

Atmospheric aerosols have been collected at four sites around Japan during 2000. From systematically monitoring the major (Na, Mg, Al, K, Ca, and Fe) and trace (Rb and Sr) elements, along with the Sr isotope composition, we have tried to estimate the contribution of long-range-transported Asian dust (“Kosa”) to the atmospheric aerosols. The results are summarized as follows: (1) The concentration of each element in the aerosols increased during the “Kosa” period. The increase was particularly obvious in samples collected on 8 April 2000, when the “Kosa Phenomenon” was observed at all the sampling sites in Japan, 2 days after a very heavy dust storm had occurred in China. (2) The Rb–Sr isotopic diagram shows a two-component mixing relationship: one with a high 87Sr/86Sr ratio and a high 87Rb/86Sr ratio, and the other with a low 87Sr/86Sr ratio and a low 87Rb/86Sr ratio. There is a significant difference between that of the expected end member of the Asian dust and that of the reported Asian loess, which is thought to be the possible source of the components of the “Kosa”, although the lower component is consistent with the local component at Wako. (3) Plots of the 87Sr/86Sr ratio vs the Ca/Al and Sr/Al ratios support a two-component mixing suggested by the Rb–Sr systematics, and they indicate that the contributing continental soil components to the “Kosa” aerosols should be composed of the silicate fraction of Asian loess. (4) The discrepancy in the Rb–Sr systematics between the expected end member and the possible sources may be caused by the dissolution of the Ca-bearing minerals via long-range dust transport, or by a combination of source characteristics and grain size separation.