Gas-phase rate coefficients of the reaction of ozone with four sesquiterpenes at 295 ± 2 KElectronic supplementary information (ESI) available. See DOI: 10.1039/c4cp05542j

The rate coefficients of the reaction of ozone with the four atmospherically relevant sesquiterpenes β-caryophyllene, α-humulene, α-cedrene and isolongifolene were investigated at 295 ± 2 K and atmospheric pressure by at least two independent experimental investigations for each reaction. Relative rate experiments were carried out in a flow tube using two different experimental approaches with GC-MS detection (RR 1) and PTR-MS analysis (RR 2) as the analytical techniques. Absolute rate coefficients were determined in a stopped-flow experiment following the ozone depletion by means of UV spectroscopy. The average rate coefficients from the combined investigations representing the mean values of the different experimental methods are (unit: cm 3 molecule −1 s −1 ): k (O 3 +β-caryophyllene) = (1.1 ± 0.3) × 10 −14 (methods: RR 1, RR 2, absolute), k (O 3 +α-humulene) = (1.2 ± 0.3) × 10 −14 (RR 1, RR 2), k (O 3 +α-cedrene) = (1.7 ± 0.5) × 10 −16 (RR 2, absolute) and k (O 3 +isolongifolene) = (1.1 ± 0.5) × 10 −17 (RR 2, absolute). The high ozonolysis rate coefficients for β-caryophyllene and α-humulene agree well with the results by Shu and Atkinson ( Int. J. Chem. Kinet ., 1994, 26 ) and lead to short atmospheric lifetimes of about two minutes with respect to the ozone reaction. The relatively small rate coefficients for α-cedrene and isolongifolene differ from the available literature values by a factor of about 2.5-6. Possible reasons for the deviations are discussed. Finally, calibrated sesquiterpene FT-IR spectra were recorded for the first time. Room temperature rate coefficients of the reaction of ozone with four sesquiterpenes were measured using absolute and relative rate techniques.