Geochemical analyses of a Himalayan snowpit profile: implications for atmospheric pollution and climate

Organic compounds, extracted from snow and ice from the Dasuopu glacier, on the Qinghai-Tibetan Plateau in Southwest China at an altitude of 7000 m ab ove sea level (asl), were identified through pre-enrichment, solvent extrac tion and subsequent CC-MS analysis. The average concentration of the extrac table organic matter reached 45.4 mu g/l. C-15-C-33 n-alkanes, C-6-C-18 n-a lkanoic acids, C-24-C-31 n-alkan-2-ones and esters were derived from subtro pical higher plants, as well as marine algae and bacteria. Organic compound s, indicative of petroleum residues such as automobile and diesel exhaust w ere also unexpectedly identified in the glacial snow. These included n-alka nes, alkylcyclohexanes, pristane, phytane, extended C-19-C-29 tricyclic ter panes, a C-24 tetracyclic terpane, C-27-C-35 alpha beta hopanes, and C-27-C -29 steranes. Their presence indicates that the remote mountainous region a nd, to some extent, the middle-upper troposphere are polluted by human acti vities. Concentrations of some organic compounds, and total extractable org anic matter, display a weak seasonal variation, postulated to be related to the location of middle-upper troposphere. The C-17 n-alkane abundance and some molecular ratios exhibit a stronger seasonal variation, which may sign ify strong climatic change. (C) 2000 Elsevier Science Ltd. All rights reser ved.