Single Particle Morphology And Mineral Composition Of Dust Aerosol Released From Tibetan Plateau Surface

The Tibetan Plateau(TP),which is the highest plateau in the world and has the largest snow and ice reservoirs other than the Antarctic and the Arctic,is known as the "Water Tower of Asia".It influences regional and even global climate change and hydrological cycles through dynamic and thermal forcings,and is among the most sensitive regions to climate change in the globe.Advanced understanding of the local release of dust aerosols from plateaus is important for assessing their climate and environmental impacts on regional and larger scales.In this study,the Portable In-Situ Wind Erosion Lab(PI-SWERL)dust generation system,which is designed to simulate the natural wind erosion and dust release process,was used to collect dust aerosol samples with particle size less than 10μm by using an aerodynamic particulate sampler.Using a computer-controlled scanning electron microscopy combined with Energy Dispersive X-ray Detector(CCSEM-EDX),72,045 single particles of dust were analyzed to obtain statistics on the particle size,shape,and elemental composition of dust released by wind erosion form four types of land use in sand dunes,Gobi,river sediments and degraded grassland in some of the dust source areas of the plateau and to compare the geomorphological and spatial differences among them.The main results are shown below:(1)The deserted surface of the plateau can contribute a large number of submicronscale dust particles,with the peak particle size distribution between 0.7–1.0μm and the median value of particle size of 1.10 ± 0.11μm.The particle size distribution of dust released by wind erosion in different sandy landscapes is less different,while the spatial distribution of particle size is more obvious,and the particle size distribution of plateau dust is mainly influenced by the location of the site.Overall,the particle number size distribution of dust aerosols follows the pattern that the percentage of larger particles is larger from west to east within the study area,while the particle number size distribution of dust aerosols in the northern TP may follow the pattern that the percentage of larger particles is smaller from south to north.The differences between the wind erosion of surface soils in the two regions may be higher than the differences between different locations within the two regions.(2)The surface soil wind erosion and dust aerosol particles of sand dunes and Gobi are relatively similar in shape,and the overall shape of wind erosion sand and dust aerosol particles of degraded grassland surface is more symmetrical but with irregular edges,while wind erosion sand and dust aerosol particles of sediment surface are larger in size,more elongated in shape and with irregular edges,with greater uncertainty.(3)The dust aerosols released by wind erosion at the surface of the TP dust source are dominated by clay minerals,feldspar and quartz,and the particles belonging to these three minerals account for 75.75 ± 21.88% of the total number fraction of all particles.The number percent content of clay minerals varied greatly between samples,with the highest content of clay minerals being 71.32% and the lowest being only 19.60%.The mineral composition of dust aerosol released form dunes and Gobi is relatively similar and is significantly different from that of both sediment and degraded grassland.The quantity percentages of quartz particles are higher in the sand aerosols released by wind erosion on the surface of sand dunes and degraded grasslands;the content of carbonates is higher in the dust aerosols released by wind erosion on the surface of degraded grasslands;the content of illite and iron oxides is higher in the dust aerosol released by wind erosion on the surface of sediments.Iron in dust aerosols released by wind erosion of sediments exists mainly as amorphous,iron oxides,etc.,while iron in dust aerosols released by wind erosion of other surface types exists mainly in aluminosilicates.The contents of illite,montmorillonite,sodium feldspar and quartz in dust aerosols released by wind erosion from sand source areas in the northern Tibetan plateau are higher than those in the Yarlung Tsangpo River and its tributary valleys,while the contents of kaolinite are lower than those in the Yarlung Tsangpo River and its tributary valleys.The mass fraction of soluble salts(sulfate and chloride salts)in dust from the TP is less than 0.1%,which implies the samples are almost unaffected by soluble salts.