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List of Abstracts 228Transformation 2.1 ID:4469 INVITED 14:00Heterogeneous chemistry in the dark: New insights into atmospheric budgets for reactive nitrogen andhalogensSteven Brown 1 , Nicholas Wagner 1 , James Roberts 1 , Hans Osthoff 2 , A.R. Ravishankara 1 , Eric Williams 1 ,Brian Lerner 1 , James Kercher 3 , Theran Riedel 4 , Glenn Wolfe 4 , Joel Thornton 41 NOAA Earth System Research Lab2 University of Calgary3 Hiram College4 University of WashingtonContact: steven.s.brown@noaa.govThe oxidative capacity of the atmosphere depends critically on the sources, sinks and lifetimes of tracespecies such as reactive nitrogen and halogen compounds. A key uncertainty in nitrogen oxide and chlorinebudgets is the efficiency with which they are consumed and / or produced by heterogeneous or multiphasereactions (i.e., those where a gas phase molecule reacts on or in a solid or liquid substrate suspended in theatmosphere) that occur in the nighttime atmosphere. Recent advances in optical instrumentation and massspectrometry have enabled detailed atmospheric measurements of these nighttime nitrogen oxide andhalogen compounds in the lower atmosphere. A key finding from recent field campaigns is that release ofClNO2 (nitryl chloride) formed from heterogeneous/multiphase uptake of N2O5 is surprisingly efficient andremarkably widespread. This halogen species is unreactive in the dark but photolyzes in sunlight to provideatomic chlorine. Production of ClNO2 spans a wide variety of environments and may represent a largefraction of the global tropospheric halogen budget. If so, tropospheric halogens may derive in large part fromanthropogenic emissions of NOx rather than from natural sources. This presentation will describe resultsfrom recent measurements of N2O5 and ClNO2 and the evidence for ClNO2 as a major source of activechlorine in the lower atmosphere.Transformation 2.2 ID:4301 14:20OH variability in the period 1988-2008 inferred from the global methyl chloroform budgetMaarten Krol 1 , Steve Montzka 2 , Jos Lelieveld 31 Wageningen University, Netherlands2 NOAA/ESRL Boulder, USA3 Max Planck Instutute for Chemistry, Mainz GermanyContact: maarten.krol@wur.nlInter-annual variability in the oxidizing capacity (the OH climate) is driven by variability in the sources andthe sinks of the OH radical. Short-wave solar radiation, ozone, and water vapor variations may inducevariations in OH production, but also the abundance of NO is known to stimulate OH recycling. Importantsinks for OH are CO and CH4, but regionally non-methane hydrocarbons can play an important role as well.Thus, many natural processes influence the OH abundance, ranging from biomass burning (CO emissions),El Nino Southern Oscillation (water vapor, wetland CH4 emissions), and the ozone layer (radiation). On topof the natural factors, anthropogenic emissions may perturb global OH chemistry, possibly leading to longtermtrends. One important question is how large the inter-annual variations in OH can be, as they provideindications about the sensitivity of the atmospheric oxidation capacity to perturbations. Previous analyses ofthe methyl chloroform budget seem to indicate that the inter-annual variability in OH is in the order of 7-8%.This, however, is at odds with the CH4 budget, that allows maximum variations in the order of maximum5%. In this contribution, a simple analysis of the methyl chloroform budget will be presented in whichrealistic assumptions about the methyl chloroform emission uncertainty are used to estimate OH variability.Preliminary results show that variability in the derived OH is smaller than 2%, with variations that can beiCACGP-IGAC 2010 15 July, 2010