Gas-Phase Kinetic Investigation of the OH-Initiated Oxidation of a Series of Methyl-Butenols under Simulated Atmospheric Conditions

Five biogenic unsaturated alcohols have been investigated under simulated atmospheric conditions regarding their gas-phase OH reactivity. The gas-phase rate coefficients of OH radicals with 2-methyl-3-buten-2-ol (k(1)), 3-methyl-2-buten-1-ol (k(2)), 3-methyl-3-buten-1-ol (k(3)), 2-methyl-3-buten-1-ol (k(4)), and 3-methyl-3-buten-2-ol (k(5)) at 298 +/- 2 K and 1000 +/- 10 mbar total pressure of synthetic air were determined under low- and high-NOx conditions using the relative kinetic technique. The present work provides for the first time the rate coefficients of gas-phase reactions of hydroxyl radicals with 2-methyl-3-buten-1-ol and 3-methyl-3-buten-2-ol. The following rate constants were measured (in 10(-11) cm(3) molecule(-1) s(-1)): k(1) = 6.32 +/- 0.49, k(2) = 14.55 +/- 0.93, k(3) = 10.04 +/- 0.78, k(4) = 5.31 +/- 0.37, and k(5) = 11.71 +/- 1.29. No significant differences in the measured rate coefficients were obtained when either 365 nm photolysis of CH3ONO in the presence of NO or 254 nm photolysis of H2O2 was used as a source of OH radicals. Reactivity toward other classes of related compounds such as alkenes and saturated alcohols is discussed. A comparison of the structure-activity relationship (SAR) estimates derived from the available accepted methodologies with experimental data available for unsaturated alcohols is provided. Atmospheric lifetimes for the investigated series of alkenols with respect to the main atmospheric oxidants are given and discussed.