Abstract
Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)×10-11 cm3 s−1 at 304 K, (4.4±0.2)×10-17 cm3 s−1 at 300 K and (4.6±1.6)×10-11 cm3 s−1 at 300 K, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the chamber experiments. In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.
Highlights
On a global scale, the emission of carbon from biogenic volatile organic compounds (BVOCs) exceeds 1000 Tg per year (Guenther et al, 2012)
Up to 100 ppmv of CO was injected into the chamber as an OH scavenger for experiments E4 and E5 to study the ozonolysis of 3-carene and the photolysis of caronaldehyde under OH-free conditions
Since there was no OH scavenger present in experiment E3, the reaction system was influenced by OH that is formed from ozonolysis
Summary
The emission of carbon from biogenic volatile organic compounds (BVOCs) exceeds 1000 Tg per year (Guenther et al, 2012). Among all BVOC emissions, monoterpenes are the second most important class of species, contributing up to 16 % to the total emissions. As they are unsaturated and highly reactive, knowledge of their atmospheric chemistry is crucial to understand the formation of secondary pollutants such as ozone (O3) and particles Of the total global annual monoterpene emissions, 3carene contributes 4.5 %, making it the seventh most abundant monoterpene species (Geron et al, 2000). Hakola et al (2012) measured the mixing ratios of monoterpenes over a boreal forest in Hyytiälä, Finland, and found 3-carene to be the second most abundant monoterpene after α-pinene. While the atmospheric chemistry of some monoterpenes such as α-pinene or β-pinene has been investigated in a number of experimental and theoretical studies
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