Effect of NOx on product yields and Arrhenius parameters of gas-phase oxidation of β-ocimene initiated by OH• radicals

Rate coefficients for the gas-phase reaction of OH center dot radicals with beta-ocimene were measured using the relative rate method over the temperature range 288-311 K at 760 Torr total pressure of nitrogen. The experiments were performed in a large volume environmental chamber using long-path FTIR spectroscopy to monitor the reactants. A room temperature rate coefficient of k((beta-ocimene+ OH)center dot()) = (2.36 +/- 0.54) x 10(-10) cm(3) molecule(-1) s(-1) was obtained for the title reaction. The temperature dependent rate coefficients are best fit by the Arrhenius expression k = (4.02 + 0.71) x 10(-14) exp(2567 + 211)/T. In addition, product studies have been performed at (298 +/- 2) K and 760 of Torr of synthetic air in the absence and presence of NOx. The following molar products were determined: formaldehyde (16.5 +/- 0.9)% and (24.3 +/- 1.5)%, acetone (45.6 +/- 2.1)% and (58.3 +/- 3.4)%, methyl vinyl ketone (18.5 +/- 0.8)% and < 5% and glycolaldehyde (7.6 +/- 0.6)% and < 5% in the absence and presence of NOx, respectively. Acetic acid (< 5%) was only found in the reaction performed in the absence of NOx. With NOx peroxy acetyl nitrate was formed with a yield < 5%. Reaction mechanisms accounting for the formation of the products are proposed and atmospheric implications are discussed.