OH- and O3-initiated atmospheric degradation of camphene: temperature dependent rate coefficients, product yields and mechanisms

Abstract

Gas-phase rate coefficients for the reactions of OH and O₃ with camphene have been measured over the temperature range 288–311 K using the relative rate method. The experiments were carried out in an environmental chamber using long-path FTIR spectroscopy to monitor the reactants. Room temperature rate coefficients (in cm³ per molecule per s) of k_{(camphene+OH)} = (5.1 ± 1.1) × 10⁻¹¹ and k_{(camphene+O3)} = (5.1 ± 1.1) × 10⁻¹⁹ were obtained for the OH and O₃ reactions, respectively. The temperature dependence of the reactions are best fit by the Arrhenius expressions (in cm³ per molecule per s) k_{(camphene+OH)} = (4.1 ± 1.2) × 10⁻¹² exp[(754 ± 44)/T] for the OH reaction and k_{(O3+camphene)} = (7.6 ± 1.2) × 10⁻¹⁸ exp[−(805 ± 51)/T] for the O₃ reaction. To the best of our knowledge, this is the first report of the temperature dependencies for the reactions of OH and O₃ with camphene. In addition, product studies have been performed at (298 ± 2) K and 760 Torr of synthetic air for the reaction of OH + camphene in the absence and presence of NO_x, and for O₃ molecules + camphene at (298 ± 2) K and 750 Torr of synthetic air. For the OH reaction the following molar product yields were obtained: acetone (10 ± 2)% and (33 ± 6)%, and formaldehyde (3.6 ± 0.7)% and (10 ± 2)% in the absence and presence of NO_x, respectively. Formaldehyde with a molar yield of (29 ± 6)% was the only product uniquely identified and quantified for the O₃ reaction.