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 (k(1)), ethyl methacrylate (k(2)) and n-butyl methacrylate(k(3)) were determined to be k(1) = (4.15 +/- 0.32) x 10(-11) cm(3) molecule(-1) s(-1), k(2) = (4.58 +/- 0.59) x 10(-11) cm(3) molecule(-1) s(-1) and k(3) = (7.08 +/- 0.75) x 10(-11) cm(3) 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. (c) 2006 Elsevier B.V. All rights reserved.