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List of Abstracts 1522 Wageningen Univ.3 SIO/UCSD4 ESRL/NOAA5 MAR/CSIRO6 PRL7 Univ. Bristol8 EAPS/MITContact: prabir@jamstec.go.jpWe have used an AGCM-based Chemistry Transport Model (ACTM) for the simulation of methylchloroform (MCF; CH 3 CCl 3 ) and methane (CH 4 ) in the height range from the earth’s surface to about 90 km.Tropospheric loss rates are calculated based on two sets of hydroxyl (OH) fields: (1) Spivakovsky et al.(2000), manually adjusted for MCF simulation by the transport model (TM5) for the period 2000-2006, (2)ACTM, manually adjusted for MCF decadal trends. Loss rates due to photolysis and chemical reactions(with Cl and O 1 D) were parameterized in the ACTM based on JPL Publication 06-2 (Sander et al., 2006) forappropriate absorption cross-sections and reaction rates. Surface emissions for the period of simulations(1988-2008) are constructed using the EDGAR3.2 emission distribution and global totals from McCullochand Midgley (2001). The model results are compared with more than two decades of surface observationsfrom the NOAA cooperative network and the multi-institutional AGAGE network, and campaign basedballoon-borne vertical profiles.The Pearson’s moment correlations for model and observed time series of separated synoptic and seasonalvariations are found to be generally greater than 0.3 (N~350) and 0.6, respectively, for individual years in theperiod of 1990-2007 at 5 AGAGE sites (Mace Head, Trinidad Head, Ragged Point, Cape Matatula, CapeGrim), where continuous measurements are available. This comparison suggests that the MCF emissioninventory and both the OH distributions in the troposphere are valid. The balloon-borne measurements ofvertical profiles in the stratosphere from Hyderabad and southern France, on an event basis, are also wellcaptured by the ACTM simulations, suggesting a realistic representation of MCF photochemistry andtroposphere-stratosphere transport. Note that the global total MCF emissions decreased from 715 Gg in1990, rapidly to 102 Gg in 1996, and then slowly to 5 Gg in 2008. The ACTM simulations show that MCF istransported from the northern (NH) to southern (SH) hemispheres through the upper troposphere in the firsthalf of the 1990s when the NH emissions were large compared to SH emissions. The equilibration in MCFconcentrations between the two hemispheres in the 2000s helps to explain the temporal evolution in MCFconcentrations, e.g., the difference between Mace Head and Cape Grim, decreased from about 50 ppt in1991 to none in 2006.The observed 50% decrease in the MCF concentration differences between the Barrow and Mauna Loa flaskobservation sites in 1996 successfully tracks the largest MCF emission decrease of from 241 Gg in 1995 to102 Gg in 1996. Further, the concentration differences simulated using Spivakovsky/TM5 OH appear to bein much closer agreement with the observed differences while the simulation using the ACTM OH tends tounderestimate by a fraction of a ppt. This underestimation of MCF concentration difference for thesimulation using ACTM OH is demonstrated clearly in the differences between the Alert and South Polesites, which are the furthest apart in terms of latitude. The NH/SH ratio of OH concentration forSpivakovsky/TM5 OH is 0.98 and it is 1.25 for the ACTM OH. The higher OH loss of MCF in the NH forthe simulation using ACTM OH results in the weaker inter-hemispheric gradient in MCF concentrations,even though both the OH fields are adjusted for simulating the MCF decadal growth rates successfully.Our results suggest that the NH/SH ratio as well as the absolute concentration of OH can be estimated usingMCF simulations, and this impacts on the simulations of other tropospheric species, such as methane andcarbon monoxide.iCACGP-IGAC 2010 14 July, 2010