Computational study on the mechanisms and rate constants of the OH-initiated oxidation of ethyl vinyl ether in atmosphere

Atmospheric degradation of 2-chloroethyl vinyl ether, allyl ether and allyl ethyl ether: Kinetics with OH radicals and UV photochemistry

Unsaturated ethers are oxygenated volatile organic compounds (OVOCs) emitted by anthropogenic sources. Potential removal processes in the troposphere are initiated by hydroxyl (OH) radicals and photochemistry. In this work, we report for the first time the rate coefficients of the gas-phase reaction with OH radicals (k_OH) of 2-chloroethyl vinyl ether (2ClEVE), allyl ether (AE), and allyl ethyl ether (AEE) as a function of temperature in the 263-358 K range, measured by the pulsed laser photolysis-laser induced fluorescence technique. No pressure dependence of k_OH was observed in the 50-500 Torr range in He as bath gas, while a slightly negative T-dependence was observed. The temperature dependent expressions for the rate coefficients determined in this work are: The estimated atmospheric lifetimes (τ_OH) assuming k_OH at 288 K were 3, 2, and 4 h for 2ClEVE, AE and AEE, respectively. The kinetic results are discussed in terms of the chemical structure of the unsaturated ethers by comparison with similar compounds. We also report ultraviolet (UV) and infrared (IR) absorption cross sections (σ_λ and σ(ν˜), respectively). We estimate the photolysis rate coefficients in the solar UV actinic region to be less than 10^-7 s^-1, implying that these compounds are not removed from the atmosphere by this process. In addition, from σ(ν˜) and τ_OH, the global warming potential of each unsaturated ether was calculated to be almost zero. A discussion on the atmospheric implications of the titled compounds is presented.

OH-initiated tropospheric photooxidation of allyl acetate: a theoretical study

The mechanisms of OH-initiated oxidation of allyl acetate in the presence of O2/NO have been investigated by performing density functional theory calculations. Two patterns (OH-addition and H-abstraction) of the initial reaction and the subsequent reactions of the primarily produced intermediates (IM1, IM2, and IM4) have been proposed. The OH-addition reactions are more favorable than the H-abstraction reactions, but H-abstraction from the CH2 group cannot be ignored. The major degradation products have been identified. The rate coefficients and the branching ratios of the primary reactions are obtained over the temperature of 200–500 K and the pressure range of 0.001–1000 atm. The total rate coefficient is 3.17 × 10−11 cm3 molecule−1 s−1 at 298 K and 1 atm. With respect to the typical concentration of OH radical (2.0 × 106 molecule cm−3), the atmospheric lifetime of AAC is estimated to be 4.40 h.