Quantitative study of the mineralogical composition of mineral dust aerosols by X-ray diffraction.

Mineral dust aerosols, produced by wind erosion in arid regions and semi-arid surfaces, are important components of the atmosphere that affect the Earth radiative budget, atmospheric chemistry and biogeochemical cycles. Dust aerosol particles are composed of a complex mixture of various minerals, mainly clays, calcite, quartz, feldspars and iron oxides. The nature and the relative abundance of the minerals are key parameters to evaluate mineral dust environmental impacts. Strong limitations remain to quantify the mineralogical composition of dust particles, mainly due to the low mass of in-situ collected dust particle samples. In this study, an analytical method and X-Ray Diffraction (XRD) measurements are presented to quantify the mineralogical composition of low mass aerosol particle samples. The method is applied on reference minerals (illite, kaolinite and palygorskite) commonly present in desert dust aerosols, as well as on lab-generated dust aerosols from desert soils. XRD measurements of theses samples in rotation in a glass capillary are combined with the Rietveld refinement method. The results obtained are repeatable and confronted to theoretical values given in the literature for the reference minerals. This method allows us to quantify the mineralogical composition of low mass dust mineral samples with an unprecedented accuracy.

[Clay ratio as a tracer to assess the origin of soil-derived dust].

The objectives of this research are to characterise the mineralogy of soil-derived dust in Northern China and to set up the mineralogical signature to trace their origin. Mineral composition of aerosol particles is investigated at five sites (Aksu, Dunhuang, Yulin, Tongliao and Changwu) during the intensive field campaign period of ACE-Asia. The results show that the Kaolinite (K) to Chlorite (C) ratio is sensitive to the regional origin of Asian dust. Western source areas (represent by Aksu) displayed the lowest K/ C ratio of 0.3 (in average), while it was found that to increase up to 0.70 (in average) as moving towards north source areas (represent by Yulin). By studying transported dust in a depositional area representative of the Chinese Loess Plateau, the usefulness of the K/C ratio to retrieve the origin of the dust by associating it with back air-mass trajectories is checked. Compared the mineralogical data between Asian dust and Sahara dust, it is shown that K/C ratio is also a good signature to identify the source areas on the global scale.