Characterization of NMHCs in downtown urban center Kathmandu and rural site Nagarkot in Nepal

The total of 28 different C-2-C-6 non-methane hydrocarbons including isopre ne emitted from natural and anthropogenic sources in urban and rural sites of Kathmandu, capital of Nepal, were characterized for the first time in Ne pal, in November 1998. Thirty-eight whole air samples were analyzed by usin g GC/FID. Ethene, acetylene and C-4-C-5 alkanes were identified as the sour ce signature in Kathmandu urban ambient air. Hydrocarbon emissions from veh icular exhaust and gasoline evaporation sources were confirmed to outweigh natural gas and biogenic sources. Comparison of NMHCs profile normalized by acetylene between Kathmandu and Tokyo, Japan showed prominent difference i n C-2-C-5 alkanes relative to acetylene. Significant amount of ethene at th e rural site was assigned as emitted from biogenic sources because of its s ignificant correlation with isoprene (R-2 = 0.52). Predominant amount of is oprene (average 278 pptv) observed at the urban site were assigned to be em itted from vehicular exhaust as its exhibited high correlation with other a nthropogenically emitted hydrocarbons (R-2 = 0.72 with acetylene). Photoche mical aging analysis showed that the mixing ratio variation of urban air tr ansporting towards the rural site took place through its OH radical initiat ed oxidation and the observed alkanes in the rural site were mostly from th e transported urban air. (C) 2000 Elsevier Science Ltd. All rights reserved .