[1] The mineralogical properties of Asian dust have been examined in detail, and the results have been compared with the Chinese source soils using high-resolution scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and chemical analysis. Mineralogical classification of Asian dust particles showed that the most common single particles were clay aggregates (48%) that were often mixed with nanosized calcite, followed by particles of quartz (22%), plagioclase (11%), coarse calcite (6%), K-feldspar (5%), muscovite, chlorite, kaolinite, amphibole, gypsum, Fe and Ti oxides which were either partly or entirely attached with clay-size mineral grains. The clay minerals in Asian dust were mostly illite and interstratified illite-smectite. The average mineral composition of the bulk dust samples by X-ray diffraction was quartz (28%), plagioclase (11%), K-feldspar (8%), calcite (8%), illite (19%), interstratified illite-smectite (22%), chlorite (2%), smectite (1%), and kaolinite (1%). In the silty soils from the source regions, the clay minerals and nanosized pedogenic calcite aggregated and covered silt-size minerals, while the sands were mostly composed of quartz and feldspars and were lined with clay minerals. The mineralogy of Asian dust was similar to that of the silty soil from the loess plateau, but the total phyllosilicate content increased from desert sands (7%), silty soil (23%), to Asian dust (45%), fining eastward. The optical properties of Asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay-rich mineral composition, the aggregation and attachment of the clay minerals on the coarser minerals, and the nanosized calcite.

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Abstract. Giant particles transported over long distances are generally of limited concern in atmospheric studies due to their low number concentrations in mineral dust and possible local origin. However, they can play an important role in regional circulation of earth materials due to their enormous volume concentration. Asian dust laden with giant particles was observed in Korea on 31 March 2012, after a migration of about 2000 km across the Yellow Sea from the Gobi Desert. Scanning electron microscopy (SEM) revealed that 20 % of the particles exceeded 10 µm in equivalent sphere diameter, with a maximum of 60 µm. The median diameter from the number distribution was 5.7 µm, which was larger than the diameters recorded of 2.5 and 2.9 µm in Asian dust storms in 2010 and 2011, respectively, and was consistent with independent optical particle counter data. Giant particles (> 10 µm) contributed about 89 % of the volume of the dust in the 2012 storm. Illite-smectite series clay minerals were the major mineral group followed by quartz, plagioclase, K-feldspar, and calcite. The total phyllosilicate content was ∼52 %. The direct long-range transport of giant particles was confirmed by calcite nanofibers closely associated with clays in a submicron scale identified by high-resolution SEM and transmission electron microscopy. Since giant particles consisted of clay agglomerates and clay-coated quartz, feldspars, and micas, the mineral composition varied little throughout the fine (< 5 µm), coarse (5-10 µm), giant-S (10-20 µm), and giant-L (> 20 µm) size bins. Analysis of the synoptic conditions of the 2012 dust event and its migration indicated that the mid-tropospheric strong wind belt directly stretching to Korea induced rapid transport of the dust, delivering giant particles. Giant dust particles with high settling velocity would be the major input into the terrestrial and marine sedimentary and ecological systems of East Asia and the western Pacific. Analysis of ancient aeolian deposits in Korea suggested the common deposition of giant particles from Asian dust through the late Quaternary Period. The roles of giant particles should be reviewed with regard to regional circulation of mineral particles and nutrients.

Mineral dust supplied to remote ocean regions stimulates phytoplankton growth through delivery of micronutrients, notably iron (Fe). Although attention is usually paid to Fe (hydr)oxides as major sources of available Fe, Fe-bearing clay minerals are typically the dominant phase in mineral dust. The mineralogy and chemistry of clay minerals in dust particles, however, are largely unknown. We conducted microscopic identification and chemical analysis of the clay minerals in Asian and Saharan dust particles. Cross-sectional slices of dust particles were prepared by focused ion beam (FIB) techniques and analyzed by transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDXS). TEM images of FIB slices revealed that clay minerals occurred as either nanothin platelets or relatively thick plates. Chemical compositions and lattice fringes of the nano-thin platelets suggested that they included illite, smectite, illite-smectite mixed layers, and their nanoscale mixtures (illite-smectite series clay minerals, ISCMs) which could not be resolved with an electron microbeam. EDXS chemical analysis of the clay mineral grains revealed that the average Fe content was 5.8 % in nano-thin ISCM platelets assuming 14 % H 2 O, while the Fe content of illite and chlorite was 2.8 and 14.8 %, respectively. In addition, TEM and EDXS analyses were performed on clay mineral grains dispersed and loaded on micro-grids. The average Fe content of clay mineral grains was 6.7 and 5.4 % in Asian and Saharan dusts, respectively. A comparative X-ray diffraction analysis of bulk dusts showed that Saharan dust was more enriched in clay minerals than Asian dust, while Asian dust was more enriched in chlorite. Clay minerals, in particular nanocrystalline ISCMs and Fe-rich chlorite, are probably important sources of Fe to remote ma-rine ecosystems. Further detailed analyses of the mineralogy and chemistry of clay minerals in global mineral dusts are required to evaluate the inputs of Fe to surface ocean microbial communities.Published by Copernicus Publications on behalf of the European Geosciences Union.