Size-segregated fluxes of mineral dust from a desert area of northern China by eddy covariance

[摘要] Mineral dust emission accounts for a substantial portion of particlespresent in the troposphere. It is emitted mostly from desert areas, mainlythrough intense storm episodes. The aim of this work was to quantifysize-segregated fluxes of mineral dust particles emitted during storm eventsoccurring in desert areas of northern China (Alashan desert, InnerMongolia), known to act as one of the strongest sources of mineral dustparticles in the Asian continent. Long-range transport of mineral dustemitted in this area is responsible for the high particle concentrationsreached in densely populated areas, including the city of Beijing. Based ona theoretical analysis, an eddy covariance system was built to getsize-segregated fluxes of mineral dust particles with optical diametersranging between 0.26 and 7.00 µm. The system was optimised to measurefluxes under intense storm event conditions. It was tested in two siteslocated in the Chinese portion of the Gobi desert. During the fieldcampaign, an intense wind erosion event, classified as a "weak duststorm", was recorded in one of them. Data obtained during this eventindicate that particle number fluxes were dominated by the finer fraction,whereas in terms of mass, coarser particle accounted for the largestportion. It was found that during the storm event, ratios of size-segregatedparticle mass fluxes remained substantially constant and a simpleparameterization of particle emission from total mass fluxes was possible. Astrong correlation was also found between particle mass fluxes and thefriction velocity. This relationship is extremely useful to investigatemechanisms of particle formation by wind erosion.

[学科分类] 大气科学