ATMOSPHERIC OXIDATION OF BIOGENIC HYDROCARBONS - REACTION OF OZONE WITH BETA-PINENE, D-LIMONENE AND TRANS-CARYOPHYLLENE

Several gas-phase carbonyl products of two terpenes, beta-pinene and D-limonene, and of the sesquiterpene, trans-caryophyllene, 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 beta-pinene, formaldehyde (yield = 0.10) and 4-acetyl-1-methylcyclohexene from D-limonene, and formaldehyde (yield 0.08) from trans-caryophyllene. The nature and yields of these products are discussed in terms of the ozone-olefin reaction mechanism. The ozone-beta-pinene reaction rate constant, measured in the presence of cyclohexane, is 12.2 +/- 1.3 x 10(-18) cm3 molecule-1 s-1 at 22 +/- 1-degrees-C. Carbonyl products have also been identified in exploratory experiments with trans-caryophyllene and NO in sunlight.