Ground observations of a strong dust storm in Beijing in March 2002

[1] On 20 March 2002, one of the most intense dust storms of the last decade struck Beijing: the total suspended particle (TSP) mass concentrations during the event reached 12 mg/m(3) and the visibility was reduced to less than 200 m. Variations in meteorological conditions in the boundary layer were monitored during the event, and changes in the physical properties and chemical composition of the aerosol also were studied. The dust storm was accompanied by a sharp and distinct increase in wind speed, a decrease in relative humidity, and increased mixing in the boundary layer due to turbulence. Back trajectory analysis and meteorological analysis showed that the main sources of dust particles that affected Beijing were most likely in southern Mongolia and the western part of Inner Mongolia, China. The amounts of Mg, Al, K, Ca, Ti, V, Cr, Mn, and Fe relative to one another were similar for the dust storm and nondust storm samples, and these elements occurred in near-crustal proportions. In contrast, both the concentrations and enrichments relative to the crustal reference material for other elements, such as Se, Ni, Pb, Br, and Cu, were much higher during the dust storm than before or afterward. These elements, which are often associated with pollution emissions, apparently originated from distant sources upstream as well as from local sources in Beijing. Even though their enrichments were lower during the dust event, the concentrations of S, Zn, and Cl during the dust storm were higher than in the nondust periods; these results are further evidence that dusty air often contains higher levels of pollutants than nondusty air.