Classification of submicron particles and the change in their number fractions in the free troposphere over Dunhuang, China

Abstract

Aerosol particles were directly collected by a balloon-borne aerosol sampler in altitude ranges of 3–9 km over Dunhuang, China (40°00'N, 94°30'E) on August 29, 2002, March 24, 2003, and March 22, 2004, in order to investigate mixture state of aerosol particles over a source area of Asian dust particles. The shape, size, and elemental compositions of the fine particles (0.2 ‹ d ‹ 1.0 μm) were individually examined (757 fine particles in total), using a scanning electron microscope and an energy dispersive X-ray analyzer. The results suggested that submicron particles could be classified into four different types: sulfate, biomass burning, mineral dust, and heavy metal particles. Sulfate particles were predominantly detected both in the diameter range of 0.3–1.0 μm and 0.2–0.3 μm. Number fractions of mineral dust particles were considerably high in the diameter range of 0.3–1.0 μm not in that of 0.2–0.3 μm, when the atmosphere was affected by high dust loading. We also found the particles derived from biomass burning and heavy metal particles in fine mode range in the free troposphere over Dunhuang.