Atmospheric oxidation of biogenic hydrocarbons: reaction of ozone with β-pinene, D-limonene and trans-caryophyllene

Several gas-phase carbonyl products of two terpenes, β-pinene and D-limonene, and of the sesquiterpene, transcaryophyllene, have been identified and their concentrations measured in experiments involving the reaction of these unsaturated biogenic hydrocarbons with ozone in the dark. Cyclohexane was added as a scavenger for the hydroxyl radical to minimize interferences from OH, which forms as a product of the ozone-hydrocarbon reaction. Carbonyl products were formaldehyde (yield = 0.42) and nopinone (yield = 0.22) from β-pinene, formaldehyde (yield = 0.10) and 4-acetyl-1-methylcyclohexene from D-limonene, and formaldehyde (yield 0.08) from transcaryophyllene. The nature and yields of these products are discussed in terms of the ozone-olefin reaction mechanism. The ozone-β-pinene reaction rate constant, measured in the presence of cyclohexane, is 12.2 ± 1.3 x 10^(-18) cm^3 molecule^(-1) s^(-1) at 22 ± 1 °C. Carbonyl products have also been identified in exploratory experiments with trans-caryophyllene and NO in sunlight