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to be ca. 1000 times lower than the average tropospheric OH radical concentrations [5]. The amount of data concerning the reactions of ethers and other oxygenated compounds with Cl atoms [1,6 -12] is not as extensive as that for the reaction with OH radicals and is increased by this study.By measurement of the rate constants for the reactions of methylethylether with OH radicals and Cl atoms the tropospheric lifetimes with respect to removal by each of these species can be estimated. Such information is important when calculating the ozone forming potential [13] of volatile organic compounds and thus assessing their contribution to atmospheric pollution.A relative rate technique has been used to obtain rate constants for the reactions of OH radicals and Cl INTRODUCTIONIn addition to being used as solvents, ethers are being added [1,2] to unleaded petrol in order to increase the octane rating and reduce the amounts of unburnt hydrocarbons, carbon monoxide, and other noxious emissions from exhausts. Ethers are mostly removed in the troposphere by their reaction with hydroxyl radicals, although chlorine atoms have recently been considered as potential tropospheric oxidants [3] ABSTRACT: The rate constants for the gas-phase reactions between methylethylether and hydroxyl radicals (OH) and methylethylether and chlorine atoms (Cl) have been determined over the temperature range 274 -345 K using a relative rate technique. In this range the rate constants vary little with temperature and average values of k MEEϩOH ϭ (6.60 Ϫ2.62 ϩ3.88 ) ϫ 10 Ϫ12 cm 3 molecule Ϫ1 s Ϫ1 and k MEEϩCl ϭ (34.9 Ϯ 6.7) ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 were obtained. The atmospheric lifetimes of methylethylether have been estimated with respect to removal by OH radicals and Cl atoms to be ca. 2 days and ca. 30 -40 days, respectively.

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