Bulk and single-particle mineralogy of Asian dust and a comparison with its source soils

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.