Preparation and chemical characterisation of an Asian mineral dust certified reference material

Surface soil was collected from 4 locations in the southern Gobi Desert in Mongolia and the pooled material was subjected to coarse sieving, cyclone classification, refinement and homogenisation, yielding 1.2 kg of a fine dust of particle diameter below 10 mu m. For certification, elemental analyses were performed by thirteen independent laboratories and, after statistical assessment of the data, 11 elements, Na, Mg, Al, K, Ca, Ti, Fe, Mn, Zn, Sr and Ba, were certified. A further 11 elements, Si, P, Sc, Cr, Co, Ni, Cu, La, Pb, Th and U, were given reference-only values. This certified reference material (CRM) has been designated NIES no. 30 Gobi Kosa Dust. We estimate the aerodynamic diameter (median diameter) of the dust to be about 4 mu m, which is within the range of median diameters (3-5 mu m) of Asian mineral dust (termed kosa in Japanese) that is wind-borne to Japan. The mineral composition of the dust based on the ratio of elemental concentration to Al concentration is very similar to those for eleven kosa dust samples collected in Japan. This new CRM also contains clay minerals and calcite that are characteristic of kosa dust. Carbonate carbon, derived from calcite, was estimated to account for about 50% of the total carbon content (2.16%) of the material. The amount of calcium extracted by 5% acetic acid solution represented about 90% of the total Ca content of the CRM. Assuming that Ca was all in the form of calcium carbonate, the carbonate carbon content was calculated to be 1.1%; this value being in good agreement with direct analysis. NIES no. 30 is considered to be a useful material for quality control purposes as well as for verification of experiments concerned with environmental behaviour of Asian mineral dust.