Abstract
Abstract. A monitoring programme for halogenated climate-altering gases has been established in the frame of the SHARE EV-K2-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. 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.
Highlights
Halocarbons (HCs) contribute to climate forcing being powerful greenhouse gases able to absorb long-wave radiation re-emitted by the Earth’s surface in the 8–13 μm atmospheric window (Ramanathan and Feng, 2009)
A slightly different schedule has been agreed for the chlorinated solvent methyl chloroform (MC) whose phase out times are 1996 and 2015 in non-Article 5 and in Article-5 (A5) countries, respectively
The objective of the study is to quantify trends in the atmospheric record of anthropogenic halocarbons in the High Himalaya, comparing our results with analogous trends recorded in other station to derive gradients
Summary
Halocarbons (HCs) contribute to climate forcing being powerful greenhouse gases able to absorb long-wave radiation re-emitted by the Earth’s surface in the 8–13 μm atmospheric window (Ramanathan and Feng, 2009). HCs containing chlorine and bromine atoms can influence the climate system via stratospheric ozone depletion. A slightly different schedule has been agreed for the chlorinated solvent methyl chloroform (MC) whose phase out times are 1996 and 2015 in non-Article 5 (nonA5) and in Article-5 (A5) countries, respectively. The second generation man-made products, i.e. the HCFCs, less aggressive toward the stratospheric ozone layer, have a more articulated and prolonged phase out schedule, implying their
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