Rate coefficients of the gas phase reactions of β-ocimene with OH and Cl radicals and O3 at 298K

E. GAONA COLMÁN; M. B. BLANCO; I. BARNES; M. A. TERUEL

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Conferencia; XIII LATIN AMERICAN CONFERENCE ON PHYSICAL ORGANIC CHEMISTRY; 2015

Several organic compounds are emitted into the atmosphere from vegetation, where isoprene and monoterpenes are the main compounds according to emissions inventories; the isoprenoids, which include isoprene, monoterpenes and some sesquiterpenes, can be emitted from all the organ plants (leaves, roots, flowers and branches) (Kesselmeier and Staudt, 1999). β-Ocimene is an acyclic monoterpene and was detected in plants such as wheat (Buttery el al, 1985), pine (Loreto et al, 2003), grass land (König et al, 1995) and tropical forest (Kesselmeier et al, 2002). In the troposphere the biogenic volatile organic compounds (BVOCs) undergo gas-phase reactions with OH radicals, NO3 radicals and O3 leading to the formation of variety groups of product species and participate in the formation of tropospheric ozone and particulate matter (Atkinson and Arey, 2003). Rate coefficients for the reaction of OH radicals, O3 molecules and Cl atoms with β-ocimene were determined by comparing their rate of decay with that of the corresponding decay of the reference compounds using the relative method. The experiments were performed in 1080 L atmospheric simulation chamber at (298 ± 2) K in 760 Torr of nitrogen coupled to an infrared spectrophotometer as a detector system. The rate coefficients obtained were k(β-ocimene + OH)= (2.36 ± 0.54) x10-10 cm3 molecule-1 s-1; k(β-ocimene + O3)= (2.19 ± 0.76) x10-16 cm3molecule-1 s-1 and k(β-ocimene + Cl)= (5.53 ± 0.98) x10-10 cm3 molecule-1 s-1. Additionally, the reactivity of the β-ocimene studied in this work is compared with other monoterpenes toward OH and Cl radicals and O3 molecules, where data are available. Tropospheric lifetimes for the β-ocimene have also been calculated and potential atmospheric implications assessed. The kinetic data and the time of residence presented here will help to a better our understanding of the atmospheric oxidation mechanisms of biogenic VOCs as terpenes and their potential contribution to the oxidizing capacity of the tropospheric and photochemical smog and SOA formation.