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.