1Service d'Aéronomie/IPSL, Université Pierre et Marie Curie-Paris 6, CNRS, France
2Spectroscopie de l'atmosphère, Chimie Quantique et Photophysique, Université Libre de Bruxelles, Brussels, Belgium
3Laboratoire des Sciences du Climat et de l'Environnement/IPSL, CEA, CNRS, UVSQ, Gif-sur-Yvette, France
4SRON Netherlands Institute for Space Research, Utrecht, Netherlands
5Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada
6Department of Chemistry, University of York, Heslington, York, UK
7Atmospheric Chemistry Div., National Center for Atmospheric Research, Boulder, CO, USA
Abstract. This study evaluates our current knowledge of pollution outflow from Asia using simulations from the LMDz-INCA global model combined with the available satellite observations of CO during the spring of 2005. CO is measured by several space-borne instruments using different techniques, allowing complementary perspectives. The CO observations from the MOPITT and SCIAMACHY nadir sounders, which provide vertically integrated information with excellent horizontal sampling, and from the ACE-FTS solar occultation instrument, which has limited spatial coverage but allows the retrieval of vertical profiles, are used. Combining observations from MOPITT (mainly sensitive to the free troposphere) and SCIAMACHY (sensitive to the full column) allow the evaluation of the boundary layer CO. Underestimated emissions in eastern Asia, and possibly too low lofting in the model, lead to an underestimate of the export to the free troposphere, as highlighted by comparisons with MOPITT and ACE-FTS. Both instruments observe large trans-Pacific transport extending from ~20° N to ~60° N, with high upper tropospheric CO observed by ACE-FTS above the eastern Pacific (with values of up to 300 ppbv around 50° N at 500 hPa and up to ~200 ppbv around 30° N at 300 hPa). The low vertical and horizontal resolutions of the global model do not allow the simulation of the strong enhancements in the observed plumes. However, the transport patterns are well captured, and are mainly attributed to export from eastern Asia, with increasing contributions from South Asia and Indonesia towards the tropics. Additional measurements of C2H2, C2H6 and HCN by ACE-FTS provide further information on the plume history. C2H2 and C2H6 enhancements are well correlated with the CO plumes, indicating common sources and rapid trans-Pacific transport. HCN observations show that the biomass burning contributes mainly at latitudes lower than ~40° N.