干旱区生态环境知识资源中心

Two dust episodes (D1: February 13 and D2: March 28-29, 2004) of long-range transport from desert and loess sources, and one dust episode (D3: March 30) mainly from local area, were investigated in spring 2004 in Beijing, China. Dust samples were collected in different dust episodes and scanning electron microscopy with X-ray energy dispersive detector (SEM/EDS) was applied to study the morphology, elemental composition, and chemical modification on the surfaces of dust particles with radius from 0.1 to 6.4 mu m. The morphological features of the particles reveal that the three dust plumes carried both dust particles (90-98% by number) and anthropogenic pollutants (e. g., fly ash and soot, 2-10%). Particle compositions show that the amount of S-containing dust particles was higher in D1 and D2 than in D3. Sulfates were introduced into the dust particles through heterogeneous uptake of SO2 during their transport. In all three dust episodes, fine dust particles (radius <1 mu m) showed a higher degree of chemical modification by SO2 compared to the coarse particles (radius >= 1 mu m). Furthermore, long-range transport dust particles were more deeply modified by SO2 than particles from local areas. The composition of the dust particles indicates that alkaline mineral components determined the level of chemical modification of individual particles. Heterogeneous uptake of SO2 on a large number of dust particles would increase mass of the internally mixed sulfates on their surfaces. The results suggest that the optical properties of dust particles during dust storm episodes are gradually altered based on how far they are transported.