Atmospheric dust aerosol over the Tibetan Plateau

Cascade impactor and bulk samples of atmospheric aerosol particles were col lected at three sites on the Tibetan Plateau: Udaoliang (September 1993 to May 1994) and Lhasa and Gongga (May 1998). The average dust concentration a t these groundbased sites was 82 mug m(-3); this is lower than the lowest a verage concentration observed over the nine major Chinese deserts (arithmet ic mean value of 270 mug m(-3)), and it also is lower than that over the Lo ess Plateau (170 mug m(-3)). The elemental mass-particle size distributions for several major dust-derived elements (Al, Ca, Fe, K, Mn, Si, and Ti) we re approximately lognormal, but those for Al, Fe, and Ti differed from Ca, K, and Si. Dry deposition velocities calculated from the observed size dist ributions and a two-layer deposition model averaged 2.7 cm(-1) for Al, Fe, and Ti. For Ca, K, and Si, which appear to be more strongly affected by loc al Tibetan sources, the average calculated dry deposition velocity was 4.3 cm s(-1). Wet deposition fluxes estimated from scavenging ratios indicate t hat less than 10% of the total deposition on the Tibetan Plateau is attribu table to wet removal during the 9 months for which data are available. The yearly mean dust deposition rate (local plus remote and dry plus wet) is es timated to be of the order of similar to 100 g m(-2) yr(-1), which is lower than that onto the Chinese desert regions (320 g m(-2) yr-1) or the Loess Plateau (250 g m(-2) yr(-1)), suggesting that the sources upwind of China, and the Tibetan Plateau itself, are not major sources for Asian dust.