THE CHEMICAL-COMPOSITION OF AEROSOLS OVER THE EASTERN HIMALAYAS AND TIBETAN PLATEAU DURING LOW DUST PERIODS

Aerosol samples were collected at four high elevation sites (> 5000 m a.s.l.) in the mountains of central Asia. The sites extend from the so uthern slopes of the Himalayas to the northern margin of the Tibetan P lateau and are representative of the natural landscape variations in t he highlands of central Asia. Daily samples were collected over period s of four days to two weeks in late summer or early autumn. This perio d is typically one of relatively low levels of dust in the Asian tropo sphere. Here we discuss the water soluble chemical composition of the aerosol samples. Tropospheric aerosols from the south slope of the Him alayas and the southern/central portions of the eastern Tibetan platea u are dominated (in order of importance) by NH4+, SO4(2-), NO3- and Ca 2+. Concentrations of these species are comparable to previously repor ted measurements in the remote troposphere. Tropospheric aerosol from the northeastern region of the Tibetan Plateau shows very high levels of Ca2+, SO4(2-), Cl-, and Mg2+ due to the influx of evaporite mineral rich dust derived from the Qaidam Basin and/or Taklamakan Desert. Our results confirm that high-elevation mountain sites in the Himalayas a nd southern/central regions of the eastern Tibetan Plateau provide iso lated platforms above the planetary boundary layer from which to inves tigate the composition of the remote continental troposphere. Fresh an d surface snow samples were also collected. The results show that the general composition and spatial pattern in summer snow chemistry is si milar to that for aerosols.