Chemical composition of Monsoon deposition in the Everest region

Between 1990 and 1994 a campaign for sampling summer depositions was carrie d out in the Everest region (Khumbu Valley, Nepal) in order to understand t he physical, chemical and transport processes responsible for the ion chemi stry 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. Conduct ivity, pH, alkalinity, the major inorganic ions and carboxylic acids were m easured and the seasonal loads were estimated. The analytical results show that the monsoon contribution dominated up to 5050 m of elevation, but it w as 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 concen tration was of the same order of magnitude of tropospheric sulphate backgro und. An intense oxidative photochemical activity of locally emitted precurs ors (NO, 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 backgrou nd tropospheric levels. (C) 1999 Published by Elsevier Science B.V. All rig hts reserved.