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.