1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
2National Centre for Atmospheric Science, NCAS, UK
3Institute of Ocean & Earth Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia
4Global Satria Life Sciences Lab, TB 12188, Taman Megajaya Phase 3, 91000 Tawau, Sabah, Malaysia
5Malaysian Meteorological Department, Ketua Stesen GAW Lembah Danum, Jabatan Meteorologi Malaysia Cawangan Sabah, Lapangan Terbang Wakuba Tawau, Peti Surat 60109, 91011 Tawau, Sabah, Malaysia
*now at: School of Biosciences, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor Darul Ehsan, Malaysia
**now at: School of Environmental and Natural Resource Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
Received: 13 Dec 2013 – Discussion started: 21 Jan 2014
Abstract. Short-lived halocarbons are believed to have important sources in the tropics, where rapid vertical transport could provide a significant source to the stratosphere. In this study, quasi-continuous measurements of short-lived halocarbons are reported for two tropical sites in Sabah (Malaysian Borneo), one coastal and one inland (rainforest). We present the observations for C2Cl4, CHBr3, CH2Br2* (actually ~80% CH2Br2 and ~20% CHBrCl2) and CH3I from November 2008 to January 2010 made using our μDirac gas chromatographs with electron capture detection (GC-ECD). We focus on the first 15 months of observations, showing over one annual cycle for each compound and therefore adding significantly to the few limited-duration observational studies that have been conducted thus far in southeast Asia. The main feature in the C2Cl4 behaviour at both sites is its annual cycle, with the winter months being influenced by northerly flow with higher concentrations, typical of the Northern Hemisphere, and with the summer months influenced by southerly flow and lower concentrations representative of the Southern Hemisphere. No such clear annual cycle is seen for CHBr3, CH2Br2* or CH3I. The baseline values for CHBr3 and CH2Br2* are similar at the coastal (overall median: CHBr3 1.7 ppt, CH2Br2* 1.4 ppt) and inland sites (CHBr3 1.6 ppt, CH2Br2* 1.1 ppt), but periods with elevated values are seen at the coast (overall 95th percentile: CHBr3 4.4 ppt, CH2Br2ast 1.9 ppt), presumably resulting from the stronger influence of coastal emissions. Overall median bromine values from [CHBr3 × 3] + [CH2Br2* × 2] are 8.0 ppt at the coast and 6.8 ppt inland. The median values reported here are largely consistent with other limited tropical data and imply that southeast Asia generally is not, as has been suggested, a hot spot for emissions of these compounds. These baseline values are consistent with the most recent emissions found for southeast Asia using the p-TOMCAT (Toulouse Off-line Model of Chemistry And Transport) model. CH3I, which is only observed at the coastal site, is the shortest-lived compound measured in this study, and the observed atmospheric variations reflect this, with high variability throughout the study period.
Revised: 22 May 2014 – Accepted: 30 Jun 2014 – Published: 21 Aug 2014
Robinson, A. D., Harris, N. R. P., Ashfold, M. J., Gostlow, B., Warwick, N. J., O'Brien, L. M., Beardmore, E. J., Nadzir, M. S. M., Phang, S. M., Samah, A. A., Ong, S., Ung, H. E., Peng, L. K., Yong, S. E., Mohamad, M., and Pyle, J. A.: Long-term halocarbon observations from a coastal and an inland site in Sabah, Malaysian Borneo, Atmos. Chem. Phys., 14, 8369-8388, doi:10.5194/acp-14-8369-2014, 2014.