Kinetics of the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds studied under simulated atmospheric conditions

Abstract

Rate constants have been measured for the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, ethylene and the organic substrate were photolysed in a Teflon bag smog chamber. Based on the value kilo+ C H = 8,1 X 10 -12 cm 3 molecule -1 s -t 4 .the following rate constants were obtained for the hydroxy~ radical reactions at 750 Torr and at 303 K in units of 10 -t2 cm 3 molecule -I s-t: CH3ONO2, 0.37-+ 0.09; C2HsONO 2, 0.48-+ 0.20; n-C3H7ONO2, 0.70 ± 0.22; C~H5OH, 3.6 -+ 0.4; CH3COCHa, 0.26 -+ 0.08; CH~CO2i-C3H 7, 3.0 -+ 0.8; CH~CO2n-C3HT, 2.4 +-0.2. The results are discussed in retation to the available literature data and the implications of the results are considered in terms of the "smog reactivity' of these molecules.

Gas phase reactions of alkyl nitrates with hydroxyl radicals under tropospheric conditions in comparison with photolysis

“…The predicted rate constant for methyl nitrate is significantly lower than the experimental values. The difference in the experimental values, 0.38 × 10 -~2 cm 3 s -~ at atmospheric pressure (Kerr and Stocker, 1986) and 0.034 × 10 -12 cm 3 s -1 at 2-3 Torr (Gaffney et al, 1986) may be explained by a pressure effect if an adduct channel exists for this molecule. In order to estimate total loss processes of the alkyl nitrates in the troposphere, the OH reactions have to be compared with other possible removal R--CH 2 --CH--ONO 2 1.00 1.14 1.87 R--CH 2 --CH 2 --ONO 2 R I R--CH2--CH2--CH--ONO 2 6.00 6.97 6.97 The experimental values are from Atkinson (1987) noted.…”

“…The values for the rate constants from this work have been combined with the previous reported data (Atkinson, 1986;Kerr and Stocker, 1986;Gaffney et al, 1986) to refine the substituent factors for the --ONO2, --CH2ONO2, --CHONO2, and --CONO2 groups which can be used to calculate the different rate constants as shown by Atkinson, 1986. A nonlinear least-square fit technique was used to minimize the sum of the differences between the experimental and the calculated data.…”

“…a Gaffney et aL (1986). b Kerr and Stocker (1986 (Gaffney and Levine, 1979). Using this estimation method, O(3p) rate constants for the abstraction of H atoms from alkyl nitrates are predicted to be two orders of magnitude lower than the measured OH rate constants.…”

“…Because of the low solubility of methyl nitrate, the loss due to wet deposition is expected to be negligible (Gaffney et al, 1986;Lee et al, 1983). At present, the most important tropospheric sink for alkyl nitrates is thought to be the reaction with OH radicals (Atkinson et al, 1982b;Kerr and Stocker, 1986). Knowledge of the rate constants for the reaction of alkyl nitrates with OH and other atmospheric species as well as for direct photolysis seems to be necessary in order to assess the atmospheric lifetime of these compounds.…”

Relative-rate study of the gas-phase reaction of hydroxy radicals with difunctional organic nitrates at 298 K and atmospheric pressure

“…Rate coefficients have been reported in the literature for the reaction of OH radicals with PAN (Wallington et al, 1984;Tsalkani et al, 1988) and a number of alkyl nitrates (Atkinson et al, 1982;Gaffney et al, 1986;Kerr and Stocker, 1986;Becker and Wirtz, 1989;Atkinson and Aschmann, 1989;Atkinson, 1990;Nielsen et al, 1991). These reactions were previously thought to proceed by H atom abstraction from the C-H bonds although the recent study by Nielsen et al (1991) suggests that both addition and abstraction pathways may be operative and that the addition pathway probably dominates for methyl and ethyl nitrate at atmospheric pressure.…”