Rapid transport of East Asian pollution to the deep tropics

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