Suchergebnisse

Abstract. Anthropogenic emissions from East Asia have increased over recent decades, and under the prevailing westerly winds, these increases have led to changes in atmospheric composition as far afield as North America. Here we show that, during Northern Hemisphere (NH) winter, pollution originating in East Asia also directly affects atmospheric composition in the deep tropics. We present observations of marked intra-seasonal variability in the anthropogenic tracer perchloroethene (C2Cl4) collected at two locations in Borneo during the NH winter of 2008/09. We use the NAME trajectory model to show that the observed enhancements in C2Cl4 mixing ratio are caused by rapid meridional transport, in the form of "cold surges", from the relatively polluted East Asian land mass. In these events air masses can move across > 30° of latitude in 4 days. We then present data from the Monitoring Atmospheric Composition and Climate reanalysis which suggests that air masses high in C2Cl4 may also contain levels of the pollutants carbon monoxide and ozone that are approximately double the typical "background" levels in Borneo. Convection in Southeast Asia can be enhanced by cold surges, and further trajectory calculations indicate that the polluted air masses can subsequently be lifted to the tropical upper troposphere. This suggests a potentially important connection between mid-latitude pollution sources and the very low stratosphere. ; This work was supported by a NERC consortium grant to the OP3 team, by NCAS, by the European Commission through the SCOUT-O3 project (505390-GOCECF2004), though the ERC ACCI project, Project No 267760, and by NERC western Pacific grant number NE/F020341/1 and NERC CAST grant number NE/J006246/1. M. J. Ashfold thanks NERC for a research studentship. A. D. Robinson acknowledges NERC for their support through small grant project NE/D008085/1. N. R. P. Harris is supported by a NERC Advanced Research Fellowship. We thank the Sabah Foundation, Danum Valley Field Centre and the Royal Society (Glen Reynolds) for field site support. This is paper number X of the Royal Society's South East Asian Rainforest Research Programme. We are grateful for use of data provided by the MACC-II project, funded by the European Union under the 7th Framework Programme. We also acknowledge use of the NAME atmospheric dispersion model and associated NWP meteorological data sets made available to us by the Met O ce. We acknowledge the significant storage resources and analysis facilities made available to us on JASMIN by STFC CEDA along with the corresponding support teams. ; This is the published version. It first appeared at: http://www.atmos-chem-phys-discuss.net/14/30705/2014/acpd-14-30705-2014.html.

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. ; This work was supported by a NERC consortium grant to the OP3 team, by NCAS, by the European Commission through the SCOUT-O3 project (505390-GOCE-CF2004) and by NERC western Pacific grant number NE/F020341/1 and NERC CAST grant number NE/J006246/1. L. M. O'Brien and M. J. Ashfold thank NERC for research studentships. A. D. Robinson acknowledges NERC for their support through small grant project NE/D008085/1. N. R. P. Harris is supported by a NERC Advanced Research Fellowship. We thank the Sabah Foundation, Danum Valley Field Centre and the Royal Society (Glen Reynolds) for field site support. The research leading to these results has received funding from the European Union's Seventh Framework Programme FP7/2007–2013 under grant agreement no. 226224 – SHIVA. We thank David Oram and Stephen Humphrey at UEA for their assistance in checking the calibration of our Aculife cylinder in May 2009. This is paper number 626 of the Royal Society's South East Asian Rainforest Research Programme. ; This is the final published version. It first appeared at http://www.atmos-chem-phys.net/14/8369/2014/acp-14-8369-2014.html.