Radical Dependence of the Yields Methacrolein and Methyl Vinyl Ketone from the OH-lnitiated Oxidation of Isoprene under NO_ x-Free Conditions

摘要

Formation yields of methacrolein (MAC), methyl vinyl ketone (MVK), and 3-methyl furan (3MF) from the hydroxyi radical (OH) initiated oxidation of isoprene were investigated under N0,-free conditions (NO, = NO + NO2) at 50 ℃ and 1 atm in a quartz reaction chamber coupled to a mass spectrometer. Yields of the primary products were measured at various OH and hydroperoxy (HO_2) radical concentrations and were found to decrease as the HOrto-isoprene-based peroxy radical (ISORO_2) concentration ratio increases. This is likely the result of a competition between ISORO_2 self- and cross-reactions that lead to the formation of the primary products, with reactions between these peroxy radicals and HO_2 which can lead to the formation of peroxides. Under conditions with HO2/ISORO_2 ratios close to 0.1, yields of MVK (15.5% ± 1.4%) and MAC (13.0% ± 1.2%) were higher than the yields of MVK (8.9% ± 0.9%) and MAC (10.9% ± 1.1%) measured under conditions with HO2/ ISORO_2 ratios close to 1. This radical dependence of the yields was reproduced reasonably well by an explicit model of isoprene oxidation, suggesting that the model is able to reproduce the observed products yields under a realistic range of atmospheric HO_2/ISORO_2 ratios.