Kinetics of the reactions of hydroxyl radicals (OH) and of chlorine atoms (Cl) with methylethylether over the temperature range 274–345 K

Abstract

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.

Atmospheric Chemistry of CH3CH2OCH3: Kinetics and Mechanism of Reactions with Cl Atoms and OH Radicals

“…We choose to cite a final value which is the average of the individual determinations together with error limits which encompass the extremes of the determinations, hence, k 18 (CH 3 CH 2 OCH 3 +OH) = (7.53 ± 2.86) × 10 −12 cm 3 molecule −1 s −1 . Within the reported ranges of uncertainty, the value of k 18 , obtained in the present work, is consistent with the value obtained by Starkey et al ( k = () × 10 −12 cm 3 molecule −1 s −1 ).…”

“…Unfortunately, there are several inconsistencies in the data of Starkey et al For example, one would expect the Cl atom rate coefficients for the short chain length ethers to follow the sequence of k CH3OCH3 < k CH3CH2OCH3 < k CH3CH2OCH2CH3 . However, the value of k (CH 3 CH 2 OCH 3 +Cl) reported by Starkey et al is greater than the recommended value for k (CH 3 CH 2 OCH 2 CH 3 +Cl) . It is difficult to understand why CH 3 CH 2 OCH 3 should react faster than CH 3 CH 2 OCH 2 CH 3 , with Cl atoms.…”

“…Starkey et al reported a value of k 15 = (3.49 ± 0.67) × 10 −10 cm 3 s −1 based on experiments using the relative rate technique. The reason for the large discrepancy between our result and that from Starkey et al is unclear, but as mentioned by Calvert et al there are additional internal inconsistencies in the work of Starkey et al Our determination of k 6 is significantly lower than the one by Starkey et al , as expected it is lower than the literature value for k (CH 3 CH 2 OCH 2 CH 3 +Cl), and it is consistent with the expected trend of reactivity for CH 3 OCH 3 , CH 3 CH 2 OCH 3 , and CH 3 CH 2 OCH 2 CH 3 with Cl atoms: k (CH 3 OCH 3 +Cl) = (1.51 ± 0.08) × 10 −10 cm 3 molecule −1 s −1 < k 15 (CH 3 CH 2 OCH 3 +Cl) < k (CH 3 CH 2 OCH 2 CH 3 +Cl) = (2.54 ± 0.17) × 10 −10 cm 3 molecule −1 s −1 (see Table ). Reaction occurs mainly at the CH 2 groups, which explains the trend of increasing reactivity with increasing alkyl chain lengths (e.g., the rate coefficient for the reaction of di‐ n ‐propyl ether with Cl is 3.7 × 10 −10 cm 3 molecule −1 s −1 .…”

“…The kinetics and atmospheric oxidation mechanisms of the symmetric short n ‐chain ethers, dimethyl ether, CH 3 OCH 3 , and diethyl ether, CH 3 CH 2 OCH 2 CH 3 , have been the subject of numerous studies in the past . By contrast, only one kinetic study of methyl ethyl ether (CH 3 CH 2 OCH 3 ), by Starkey et al , exists in the literature. No study of the end products of the atmospheric oxidation of CH 3 CH 2 OCH 3 exists.…”

Atmospheric chemistry of C4F9OC2H5 (HFE-7200), C4F9OCH3 (HFE-7100), C3F7OCH3 (HFE-7000) and C3F7CH2OH: temperature dependence of the kinetics of their reactions with OH radicals, atmospheric lifetimes and global warming potentials

“…Furthermore, reactions with O atoms are generally much slower than OH reactions for ethers and alcohols. [12], [14], [15], [16]and [17] Consequently, under our experimental conditions, the effect of O-atom formation on the kinetic measurements can be considered negligible. k 9 = 1.9 × 10 -11 exp(240/T) cm 3 molecule -1 s -1 (230-360K) [12] Br 2 was added in excess upstream of region (2) at inlet 2, and the depletion of the Br 2 was measured by monitoring its peak at m/e = 160.…”