Chemical composition of Monsoon deposition in the Everest region

Abstract

Between 1990 and 1994 a campaign for sampling summer depositions was carried out in the Everest region (Khumbu Valley, Nepal) in order to understand the physical, chemical and transport processes responsible for the ion chemistry in the deposition of this region. Wet and bulk depositions at 5050 m a.s.l. and snow samples from 5515 to 7400 m altitude were collected. Conductivity, pH, alkalinity, the major inorganic ions and carboxylic acids were measured and the seasonal loads were estimated. The analytical results show that the monsoon contribution dominated up to 5050 m of elevation, but it was not a source of acidifying species; the transport of chemical compounds at higher altitude was due to the local breezes. At this altitude (5050 m a.s.l.) relatively high levels of nitrate and ammonium must be due to local or regional biogenic and anthropogenic inputs; non-sea-salt sulphate concentration was of the same order of magnitude of tropospheric sulphate background. An intense oxidative photochemical activity of locally emitted precursors (NOx and VOC) is probably responsible for the high levels of carboxylic acids and nitrate. Above 6000 m altitude no monsoon or regional influences were found and the measured concentration should be indicative of background tropospheric levels.