Kinetic Study of Gas-Phase Reactions of OH and NO3 Radicals and O3 with iso-Butyl and tert-Butyl Vinyl Ethers

Gas-Phase Ozone Reaction Kinetics of a Series of cis-3-Hexenyl Esters under Simulated Atmospheric Conditions

This relative kinetic study presents the experimental results obtained from the investigation of the gas-phase ozonolysis of seven biogenic unsaturated hexenyl esters under atmospheric relevant conditions at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. Various cis-3-hexenyl esters were selected for the present study since these are ubiquitous biogenic atmospheric constituents emitted by green leaf plants. The series consists of cis-3-hexenyl formate (Z3HF), cis-3-hexenyl acetate (Z3HAc), cis-3-hexenyl isobutyrate (Z3HiB), cis-3-hexenyl 3-methylbutanoate (Z3H3MeB), cis-3-hexenyl hexanoate (Z3HH), cis-3-hexenyl cis-3-hexenoate (Z3HZ3H), and cis-3-hexenyl benzoate (Z3HBz). The obtained experimental gas-phase reaction rate coefficients are as follows (in 10-17 cm3 molecule-1 s-1): (4.5 ± 0.5) for Z3HF, (5.5 ± 0.6) for Z3HAc, (7.9 ± 0.9) for Z3HiB, (11.9 ± 1.3) for Z3H3MeB, (15.3 ± 1.7) for Z3HH, (22.5 ± 2.5) for Z3HZ3H, and (29.1 ± 3.2) for Z3HBz, respectively. This study provides the first determination of the gas-phase rate coefficients of ozone with cis-3-hexenyl isobutyrate, cis-3-hexenyl 3-methylbutanoate, cis-3-hexenyl hexanoate, cis-3-hexenyl cis-3-hexenoate, and cis-3-hexenyl benzoate. A comparison of the results with available literature data and structure-activity relationship estimates was performed with emphasis placed on the structural features. The reactivity trend is discussed within this series, and estimates for the photochemical ozone creation potential (POCP) index are provided. Also, the atmospheric average lifetime of the investigated cis-3-hexenyl esters, with respect to O3 reaction, and for comparison purposes also to the OH, NO3, and Cl driven processes, were evaluated and provided within this study.

Atmospheric insight into the reaction mechanism and kinetics of isopropenyl methyl ether (i-PME) initiated by OH radicals and subsequent oxidation of product radicals

Studies on primary gas-phase reactions of emitted saturated and unsaturated ethers with oxidants and subsequent secondary reactions of product radicals with O₂ in the presence of NO are important in their atmospheric chemical processes. To accomplish these findings, we have examined the chemistry of OH-initiated oxidation of isopropenyl methyl ether (i-PME) CH₃C(CH₂)OCH₃ by electronic structure ca using density functional theory. Our energetic calculations show that OH additions to carbon-carbon double bonds of i-PME are more favorable reaction pathways than H-abstraction reactions from the various CH sites of the titled molecule. The rate constant values which are obtained from the transition state theory also signify that OH-addition reactions have faster reaction rates than H-abstraction reactions. Our calculated total rate constant of the reaction is found 9.90 × 10^-11 cm³ molecule^-1 s^-1. The percentage branching ratio calculations imply that OH-addition reactions have 98.09% contribution in the total rate constant. The atmospheric lifetime of i-PME is found to be 2.8 h. Further, we have identified 2-hydroxy-2-methoxypropanol, methyl acetate, methy-1,2-hydroxyacetate and 1-hydroxypropane-2-one, 1,2-dihydroxypropan-2-yl format, 2-hydroxyacetic acid, acetic acid, and formaldehyde from the secondary oxidation of product radicals.

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.

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

The hydroxylation reactions of ethyl vinyl ether (EVE) in the present of O2 and NO are analyzed by using MPWB1K/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of theory. According to the calculated thermodynamic data, the detailed reaction mechanisms of EVE and OH are proposed. All of the ten possible reaction pathways are discussed. The major products of the title reaction are ethyl formate and formaldehyde, which is in accordance with experimental detection. The rate constants of the primary reactions over the temperature of 250-400K and the pressure range of 100-2000Torr are computed by employing MESMER program. At 298K and 760Torr, OH-addition channels are predominate and the total rate constant is ktot=4.53×10(-11)cm(3)molecule(-1)s(-1). The Arrhenius equation is obtained as ktot=6.27×10(-12)exp(611.5/T), according to the rate constants given at different temperatures. Finally, the atmospheric half life of EVE with respect to OH is estimated to be 2.13h.