Kinetics of the reaction of OH radicals with a series of ethers under simulated atmospheric conditions at 295 K

Abstract

Ethers are being increasingly used as motor fuel additives to increase the octane number and to reduce CO emissions. Since their reaction with hydroxyl radicals (OH) is a major loss process for these oxygenated species in the atmosphere, we have conducted a relative rate study of the kinetics of the reactions of OH radicals with a series of ethers and report the results of these measurements here. Experiments were performed under simulated atmospheric conditions; atmospheric pressure (2740 torr) in synthetic air a t 295 K. Using rate constants of 2.53 x lo-", and 1.35 x lo-'' cm3 molecule-' s-l for the reaction of OH radicals with n-butane and diethyl ether, the following rate constants were derived, in units of lo-" cm3 molecule-' sf': dimethylether, (0.232 2 0.023); di-n-propylether, (1.97 2 0.08); di-n-butylether, (2.74 2 0.32); di-n-pentylether, (3.09 5 0.26); methyl-t-butylether, (0.324 2 0.008); methyl-nbutylether, (1.29 * 0.03); ethyl-n-butylether, (2.27 2 0.09); and ethyl-t-butylether, (0.883 0.026). Quoted errors represent 2u from the least squares analysis and do not include any systematic errors associated with uncertainties in the reference rate constants used to place our relative measurements on an absolute basis. The implications of these results for the atmospheric chemistry of ethers are discussed.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

“…They have been evaluated with F c =0.6. Relative rate coefficients near 1 bar from , Atkinson and Aschmann (1985) and Wallington et al (1988) are in good agreement with the preferred values. A branching ratio of 0.19 ± 0.05 for formation of cis-vs trans-isomers of the CHCl=CH adduct was determined by Zhu et al (1994) and extrapolated with F c =0.6.…”

“…The measured temperature dependencies Wallington et al, 1988;Mellouki et al, 1995;Arif et al, 1997; are in reasonable agreement. The preferred values are based on the absolute rate coefficient studies of Tully and Droege (1987), Mellouki et al (1995), Arif et al (1997) and , the rate coefficients of which are in good agreement and which are between those of the other two absolute temperature-dependent studies of and Wallington et al (1988).…”

“…In view of the small temperature coefficients reported in most of these studies, together with the relatively large associated error limits, we have selected a temperature-independent rate coefficient k based on k 298 . Thus, from the data of , Anastasi et al (1983, Wallington et al (1988), Bauer et al (1992) and, the average value of k obs =1.03×10 −13 cm 3 molecule −1 s −1 at 298 K is obtained. Taking k 2 /k=0.62 at 298 K (the mean of the data of , Anastasi et al (1983) and ) yields the recommended value of k 298 =6.4×10 −14 cm 3 molecule −1 s −1 .…”

“…Taking k 2 /k=0.62 at 298 K (the mean of the data of , Anastasi et al (1983) and ) yields the recommended value of k 298 =6.4×10 −14 cm 3 molecule −1 s −1 . The data of Wallington et al (1989) show that k 3 /k≤0.06. The rate coefficient of Atkinson and Hudgens (1997) is in agreement with the recommendations.…”

“…The reported room temperature absolute Wallington et al, 1988;Mellouki et al, 1995;Arif et al, 1997; and relative Wallington et al, 1989; rate coefficients exhibit appreciable scatter, covering a range of a factor of 1.6. The measured temperature dependencies Wallington et al, 1988;Mellouki et al, 1995;Arif et al, 1997; are in reasonable agreement.…”