Abstract
Abstract. Mineral dust interacts with incoming/outgoing radiation, gases, other aerosols, and clouds. The assessment of its optical and chemical impacts requires knowledge of the physical and chemical properties of bulk dust and single particles. Despite the existence of a large body of data from field measurements and laboratory analyses, the internal properties of single dust particles have not been defined precisely. Here, we report on the mineralogical organization and internal structures of individual fine ( < 5 µm) Saharan dust particles sampled at Tenerife, Canary Islands. 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 the focused ion beam technique were analyzed by transmission electron microscopy (TEM) to probe the particle interiors. TEM analysis showed that the most common particle type was clay-rich agglomerate, dominated by illite–smectite series clay minerals with subordinate kaolinite. Submicron grains of iron (hydr)oxides (goethite and hematite) were commonly dispersed through the clay-rich particles. The median total volume of the iron (hydr)oxide grains included in the dust particles was estimated to be about 1.5 % vol. The average iron content of clay minerals, assuming 14 wt % H2O, was determined to be 5.0 wt %. Coarse mineral cores, several micrometers in size, were coated with thin layers of clay-rich agglomerate. Overall, the dust particles were roughly ellipsoidal, with an average axial ratio of 1.4 : 1.0 : 0.5. The mineralogical and structural properties of single Saharan dust particles provide a basis for the modeling of dust radiative properties. Major iron-bearing minerals, such as illite–smectite series clay minerals and iron (hydr)oxides, were commonly submicron- to nano-sized, possibly enhancing their biogeochemical availability to remote marine ecosystems lacking micronutrients.
Highlights
We report on the mineralogical organization and internal structures of individual fine ( < 5 μm) Saharan dust particles sampled at Tenerife, Canary Islands
Cross-sectional slices of Saharan dust particles prepared by the focused ion beam technique were analyzed by transmission electron microscopy (TEM) to probe the particle interiors
A total of 48 focused ion beam (FIB) slices were prepared from 48 dust particles and analyzed using a JEOL JEM 3010 transmission electron microscope for lattice-fringe imaging and a JEOL JEM 2010 transmission electron microscope equipped with an Oxford X-MAX energy-dispersive X-ray spectrometry (EDXS) system for internal-structure imaging and chemical analysis
Summary
Mineral dust affects Earth’s climate and ecosystems via interaction with electromagnetic radiation (Sokolik and Toon, 1996; Tegen and Lacis, 1996; Formenti et al, 2011), acidic gases, and anthropogenic aerosols (Dentener et al, 1996; Ooki and Uematsu, 2005; Laskin et al, 2005); by becoming ice nuclei (Kulkarni and Dobbie, 2010; Freedman, 2015); and by delivering micronutrients to remote ocean and terrestrial environments (Swap et al, 1992; Mahowald et al, 2009; Johnson and Meskhidze, 2013). A practical method for the acquisition of data on the internal properties, was transmission electron microscopy (TEM) for thin cross-sectional slices prepared from single dust particles by the FIB technique With these improvements, Jeong and Nousiainen (2014) reported internal structures and mineralogical makeup of single particles of Asian dust which could be classified into several structural types. To extend the mineralogical and structural analyses of Asian dust particles conducted by Jeong and Nousiainen (2014), we have conducted a similar analysis of FIB slices prepared from fine Saharan dust particles collected for single-particle electron microscopic analysis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
