Kinetic and mechanistic study of the gas-phase reaction of ozone with γ-terpinene

Abstract

The ozone reaction of γ-terpinene (1-isopropyl-4-methyl-1,4-cyclohexadiene), a monoterperne emitted by Elm, Cypress, Waterhickory and Maple trees, has been investigated at 294 ± 2 K, atmospheric pressure and under dry conditions (relative humidity, RH < 2%) in two simulation chambers of the LPCA laboratory in Dunkerque (France): CHARME (CHamber for the Atmospheric Reactivity and the Metrology of the Environment) a 9.2 m3 evacuable cylinder in stainless steel electropolished and LPCA-ONE an 8 m3 cubic reactor in PMMA. Cyclohexane was used to scavenge the hydroxyl radicals formed from the rearrangement of the Criegee biradicals. The concentrations of the organic compounds were monitored versus the time with a PTR-ToF-MS and a TD-GC-FID. The rate coefficient for the γ-terpinene reaction with ozone has been determined using the pseudo-first-order and the relative-rate methods. The values obtained with both methods are in a very good agreement and give an average value of (2.10 ± 0.11) × 10−16 cm3 molecule−1 s−1 which leads to an atmospheric lifetime of 32 min for γ-terpinene with respect to its ozonolysis reaction. The main oxidation products observed and their respective molar yields (in %) include formic acid (7–11), glyoxal and/or acetone (4–9), 3-oxobutanal (6–8), 4-methyl-3-oxopentanal (5–8), acetic acid (5–9), acetaldehyde (3–6), formaldehyde (3–6), 3-oxopropanoic acid (2–4) and an unidentified compound with m/z 73.0 (2–3). The kinetic data are compared with the literature, and the reaction mechanism is discussed. To our knowledge this work represents the first mechanistic study for the ozonolysis reaction of γ-terpinene.