Temperature dependence of the yields of methacrolein and methyl vinyl ketone from the OH-initiated oxidation of isoprene under NOx-free conditions

Yields of methacrolein (MAC) and methyl vinyl ketone (MVK) from the OH-initiated oxidation of isoprene were measured under NOx-free conditions at 303, 323 and 343 K and 1 atm in a quartz reaction chamber coupled to a mass spectrometer. Measured yields of MAC and MVK were approximately 9–11% and 17−22%, respectively at temperatures between 303 and 343 K, in good agreement with previous studies. The measured yields of MAC and MVK, at 303 and 323 K as well as the measured yield of MAC at 343 K were reproduced reasonably well using an explicit model of isoprene oxidation. However, the experimental yields of MVK at 343 K were underestimated by the model, suggesting that a temperature dependent source of MVK was missing. Several recently proposed additions to the isoprene oxidation mechanism, including 1,6- and 1,5-H shift isomerization reactions of isoprene-based hydroxyalkyl peroxy radicals, were tested in order to determine if these mechanisms can explain the observed temperature dependence of the product yields.