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List of Abstracts 1251 University of Leeds2 LATMOS3 Deutsch Zentrum Luftund RaumfahrtContact: s.monks@see.leeds.ac.ukPrevious comparisons of global chemical transport models have shown that they exhibit large variability intheir Arctic chemical budgets. This indicates that the processes controlling Arctic tropospheric compositionare not well understood or represented within models. New in-situ gas-phase datasets collected during thePOLARCAT campaign are now available. This provides an opportunity to evaluate a 3-D chemical transportmodel in the challenging Arctic environment and understand the current weaknesses in such models. Tofurther compliment the analysis, retrievals from the TES instrument aboard the AURA satellite and Arcticsurface station data has also been utilised. This allows the model to be tested at a variety of locations and ona range of time-scales looking at the model’s representation of the seasonal cycle and inter-annual variabilityof CO and O3.Results show that the standard model is unable to simulate observed concentrations of CO and also overestimatesthe stratospheric flux of O3 to the Arctic troposphere. This has led to a re-evaluation of COsources and sinks in the region. Different emissions datasets for both biomass burning and anthropogenicsources have been tested within the model at different temporal resolutions. A particular focus of the workhas been on the treatment of boreal biomass burning within models and quantifying its contribution to theArctic troposphere compared to anthropogenic sources.P-Transformation.7 ID:4200 10:30Global evolution of chemical tracersStephanie Higgs, John MethvenUniversity of ReadingContact: s.a.higgs@rdg.ac.ukGlobal mass conservation in advection schemes is an important requirement when using a chemical transportmodel. This is because when analysing the change in chemical tracers over time it has to be possible to beable to differentiate between changes in mass that arise due to the numerics and those that are due to thechemistry. Most models include a fix in order to maintain mass conservation and counter the numericalchanges to tracer mass. A model that is conservative over time without needing a ‘mass fix’ term would bebeneficial as they are not always accurate. A mass fix term will also not counter spurious features in thetracer field that may arise from the numerics. This work focuses on conservation within a global traceradvection model. The model uses a finite volume scheme and so is inherently mass conservative. The modeluses an upwind advection scheme based on the NIRVANA scheme and all tracers are passive. The mainchange made to improve the conservation of the model involved a grid alteration over the Polar Regions.The resulting experiments revealed that in the case of winds specified analytically (such as solid bodyrotation) the model produced mass change on the order of a fraction of a percent over the period of a month.Global tracer mass is not accurately conserved when driven by analyses, even though the continuity equationis used to obtained vertical velocity from horizontal divergence and surface pressure. The non-conservationarises through time variation in the winds. The error is much smaller with ERA-Interim (2.5% change over 6months) than with earlier analyses (15%) indicating that ERA-Interim is more consistent in time. Theimplementations for stratospheric ozone hole simulations are discussed.iCACGP-IGAC 2010 14 July, 2010