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List of Abstracts 169range transport is estimated to be 8-11 ppbv during January-March. Role of springtime biomass burning isstudied and enhancements in ozone and BC levels at Nainital due to fires are estimated to be ~18 ppbv and~1725 ng/m3 respectively. Significant influences of biomass burning on tropospheric column NO2, aerosolproperties and lower tropospheric CO over Northern India are seen. The clear sky shortwave aerosolradiative forcing at the surface and TOA during fire-impacted periods is seen to increase by about 26 and 8W/m2 with respect to low fire activity periods. More detail on results, including preliminary results of ozonevertical distributions will be presented.P-Observations 2.12 ID:4567 10:30Modelling the multi-isotope composition of CO and related trace gases with the comprehensive AC-GCM EMAC.Sergey Gromov 1 , Patrick Jöckel 2 , Rolf Sander 1 , Carl A.M. Brenninkmeijer 11 Max Planck Institute for Chemistry2 Deutsches Zentrum für Luft-und Raumfahrt (DLR), Institut für Physik der AtmosphäreContact: sergey.gromov@mpic.deThe unique information on sources, chemical modification and sinks of atmospheric trace gases can beinferred from their isotope composition. An appropriate modelling approach is vital to the interpretation anduse of an increasing number of isotope analyses. However, the exact implementation of isotopic informationis a challenge, and many studies use simplifications which limit their applicability. We present a modellingstudy with an elaborate isotopic chemistry mechanism employed in the atmospheric chemistry generalcirculation model EMAC. The Modular Earth Submodel System (MESSy) framework incorporated inEMAC allows an explicit, more realistic treatment of the isotope effects (i.e. fractionation in chemical andphysical processes) per species basis. Conformably, we present the results of the global modelling of thestable carbon and oxygen isotope composition of the bulk of tracers, with a focus on carbon monoxide. Thesensitivity of the CO isotopic composition to the key atmospheric processes is estimated; in particular, weinvestigate the yield of CO from methane, the only distinctively 13C-depleted source of carbon in CO. Theisotope mass balance imposes yield values significantly lower than unity, pointing to efficient removalprocesses acting upon the intermediates of the CH4 to CO conversion chain. In contrast to prevalentsimplified approaches, in EMAC the yield is a diagnosed variable, rather than an assumed one.Concurrently, the first-time a global synthesis of the mass-independently fractionated (MIF) oxygen isotopecomposition of CO is presented. The intrinsic MIF enrichment in CO induced by its oxidation by OH versusthe ozone-impelled MIF source effect (due to reactions with unsaturated hydrocarbons) is assessed. Thelatter is found to be as large as +1‰ and +0.7‰ in ∆17O(CO) for NH and SH, respectively, a relativelyminor enrichment compared to the dominating OH effect of +4‰ to +6‰ in background air. This renders aconsiderable importance of CO MIF for studying the OH budget.P-Observations 2.13 ID:4471 10:30Temperature, relative humidity, mass divergence, and ozone response to strong rainfall events in thewestern tropical Pacific: Observations and modelsToni MitovskiDalhousie UniversityContact: tn648214@yahoo.comStrong precipitation events are identified at several locations in the western tropical Pacific using the TRMM3B42 gridded rainfall product. Radiosonde (IGRA) and Ozonesonde (SHADOZ) soundings are then used toiCACGP-IGAC 2010 14 July, 2010