On the OH-initiated degradation of methacrylates in the troposphere: Gas-phase kinetics and formation of pyruvates

Rate coefficients for the gas-phase reactions of OH radicals with methyl methacrylate (k1), ethyl methacrylate (k2) and n-butyl methacrylate(k3) were determined to be k1 = (4.15 ± 0.32) × 10−11 cm3 molecule−1 s−1, k2 = (4.58 ± 0.59) × 10−11 cm3 molecule−1 s−1 and k3 = (7.08 ± 0.75) × 10−11 cm3 molecule−1 s−1, respectively. We performed kinetic experiments at room temperature and atmospheric pressure of air in the presence of NO using the relative-rate technique with GC-FID analysis. This is the first kinetic study of the reactions of OH radicals with ethyl methacrylate and n-butyl methacrylate. Additionally, product identification under atmospheric conditions was performed for the first time for these unsaturated esters by the GC-MS technique. Methyl-pyruvate, ethyl-pyruvate and n-butyl pyruvate were observed as degradation products in accordance with the addition of OH to the less substituted carbon atom of the double bond, followed by decomposition of the 1-2-hydroxyalcoxy radicals formed. Kinetic data were used to estimate the atmospheric lifetimes of the esters studied.