The chemical composition of aerosols over the Eastern Himalayas and Tibetan plateau during low dust periods

Abstract

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 southern slopes of the Himalayas to the northern margin of the Tibetan Plateau and are representative of the natural landscape variations in the highlands of central Asia. Daily samples were collected over periods of four days to two weeks in late summer or early autumn. This period is typically one of relatively low levels of dust in the Asian troposphere. Here we discuss the water soluble chemical composition of the aerosol samples. Tropospheric aerosols from the south slope of the Himalayas and the southern/central portions of the eastern Tibetan plateau are dominated (in order of importance) by NH 4 +, SO 4 2−, NO 3 − and Ca 2+. Concentrations of these species are comparable to previously reported measurements in the remote troposphere. Tropospheric aerosol from the northeastern region of the Tibetan Plateau shows very high levels of Ca 2+, SO 4 2−, Cl −, and Mg 2+ 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 and southern/central regions of the eastern Tibetan Plateau provide isolated platforms above the planetary boundary layer from which to investigate the composition of the remote continental troposphere. Fresh and surface snow samples were also collected. The results show that the general composition and spatial pattern in summer snow chemistry is similar to that for aerosols.