Long-range transport of giant particles in Asian dust identified by physical, mineralogical, and meteorological analysis

摘要

Giant particles transported over long distances are generally of limitedconcern in atmospheric studies due to their low number concentrations inmineral dust and possible local origin. However, they can play an importantrole in regional circulation of earth materials due to their enormous volumeconcentration. Asian dust laden with giant particles was observed in Korea on31 March 2012, after a migration of about 2000 km across the Yellow Sea fromthe Gobi Desert. Scanning electron microscopy (SEM) revealed that 20% ofthe particles exceeded 10 μm in equivalent sphere diameter, with amaximum of 60 μm. The median diameter from the number distributionwas 5.7 μm, which was larger than the diameters recorded of 2.5 and2.9 μm in Asian dust storms in 2010 and 2011, respectively, and wasconsistent with independent optical particle counter data. Giant particles(>10 μm) contributed about 89% of the volume of thedust in the 2012 storm. Illite–smectite series clay minerals were the majormineral group followed by quartz, plagioclase, K-feldspar, and calcite. Thetotal phyllosilicate content was ~52%. The direct long-rangetransport of giant particles was confirmed by calcite nanofibers closelyassociated with clays in a submicron scale identified by high-resolution SEMand transmission electron microscopy. Since giant particles consisted of clayagglomerates and clay-coated quartz, feldspars, and micas, the mineralcomposition 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 synopticconditions of the 2012 dust event and its migration indicated that themid-tropospheric strong wind belt directly stretching to Korea induced rapidtransport of the dust, delivering giant particles. Giant dust particles withhigh settling velocity would be the major input into the terrestrial andmarine sedimentary and ecological systems of East Asia and the westernPacific. Analysis of ancient aeolian deposits in Korea suggested the commondeposition of giant particles from Asian dust through the late QuaternaryPeriod. The roles of giant particles should be reviewed with regard toregional circulation of mineral particles and nutrients.