ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-3431-2011 Three-year observations of halocarbons at the Nepal Climate Observatory at Pyramid (NCO-P, 5079 m a.s.l.) on the Himalayan range Maione M. 1 5 Giostra U. 1 5 Arduini J. 1 5 Furlani F. 1 5 Bonasoni P. 2 Cristofanelli P. 2 Laj P. 3 Vuillermoz E. 4 University of Urbino, DiSBeF, Urbino, Italy CNR-Institute for Atmospheric Sciences and Climate, Bologna, Italy Laboratoire de Glaciologie et Géophysique de l'Environnement, Université Grenoble 1-CNRS, Grenoble, France Ev-K<sup>2</sup>-CNR Committee, Bergamo, Italy CINFAI, National Consortium of Universities for Atmospheric and Hydrospheric Physics, Italy 12 04 2011 11 7 3431 3441 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/3431/2011/acp-11-3431-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/3431/2011/acp-11-3431-2011.pdf

A monitoring programme for halogenated climate-altering gases has been established in the frame of the SHARE EV-K<sup>2</sup>-CNR project at the Nepal Climate Laboratory – Pyramid in the Himalayan range at the altitude of 5079 m a.s.l. The site is very well located to provide important insights on changes in atmospheric composition in a region that is of great significance for emissions of both anthropogenic and biogenic halogenated compounds. Measurements are performed since March 2006, with grab samples collected on a weekly basis. The first three years of data have been analysed. After the identification of the atmospheric background values for fourteen halocarbons, the frequency of occurrence of pollution events have been compared with the same kind of analysis for data collected at other global background stations. The analysis showed the fully halogenated species, whose production and consumption are regulated under the Montreal Protocol, show a significant occurrence of "above the baseline" values, as a consequence of their current use in the developing countries surrounding the region, meanwhile the hydrogenated gases, more recently introduced into the market, show less frequent spikes. <br><br> Atmospheric concentration trends have been calculated as well, and they showed a fast increase, ranging from 5.7 to 12.6%, of all the hydrogenated species, and a clear decrease of methyl chloroform (−17.7%). The comparison with time series from other stations has also allowed to derive Meridional gradients, which are absent for long living well mixed species, while for the more reactive species, the gradient increases inversely with respect to their atmospheric lifetime. The effect of long range transport and of local events on the atmospheric composition at the station has been analysed as well, allowing the identification of relevant source regions the Northern half of the Indian sub-continent. Also, at finer spatial scales, a smaller, local contribution of forest fires from the Khumbu valley has been detected.

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