Mineral dust interacts with incoming/outgoing radiation, gases, otheraerosols, and clouds. The assessment of its optical and chemical impactsrequires knowledge of the physical and chemical properties of bulk dust andsingle particles. Despite the existence of a large body of data from fieldmeasurements and laboratory analyses, the internal properties of single dustparticles have not been defined precisely. Here, we report on themineralogical organization and internal structures of individual fine( 5 µm) Saharan dust particles sampled at Tenerife, CanaryIslands. The bulk of Tenerife dust was composed of clay minerals (81 %),followed by quartz (10 %), plagioclase (3 %), and K-feldspar(2 %). Cross-sectional slices of Saharan dust particles prepared by thefocused ion beam technique were analyzed by transmission electron microscopy(TEM) to probe the particle interiors. TEM analysis showed that the mostcommon particle type was clay-rich agglomerate, dominated by illite–smectiteseries clay minerals with subordinate kaolinite. Submicron grains of iron(hydr)oxides (goethite and hematite) were commonly dispersed through theclay-rich particles. The median total volume of the iron (hydr)oxide grainsincluded in the dust particles was estimated to be about 1.5 % vol. Theaverage iron content of clay minerals, assuming 14 wt % HO, wasdetermined to be 5.0 wt %. Coarse mineral cores, several micrometers insize, were coated with thin layers of clay-rich agglomerate. Overall, thedust particles were roughly ellipsoidal, with an average axial ratio of1.4 : 1.0 : 0.5. The mineralogical and structural properties of singleSaharan dust particles provide a basis for the modeling of dust radiativeproperties. Major iron-bearing minerals, such as illite–smectite series clayminerals and iron (hydr)oxides, were commonly submicron- to nano-sized,possibly enhancing their biogeochemical availability to remote marineecosystems lacking micronutrients.
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