OH- and O3-initiated atmospheric degradation of camphene: Temperature dependent rate coefficients, product yields and mechanisms

ELIZABETH GAONA COLMÁN; MARÍA BELÉN BLANCO; IAN BARNES; MARIANO A. TERUEL

Congreso; VI Congreso Argentino de la Sociedad de Toxicología y Química Ambiental de Argentina (SETAC, Capítulo Argentino); 2016

Camphene (2, 2-dimethyl-3-methylenebicyclo[2.2.1]heptane) is a bicyclic monoterpene, which is emitted to the atmosphere by vegetation. It is one of the most abundant monoterpenes emitted from plants such as Pinus sylvestris (Komenda and Koppmann. 2002), Abies alba (Moukhtar et al. 2006) and Echinacea species (Mazza and Cottrel. 1999). Gas-phase rate coefficients for the OH + camphene and O3 + camphene reactions were measured using the relative rate method over the temperature range 288-311K. The experiments were carried out in an environmental chamber using long-path FTIR spectroscopy to monitor the reactants. The temperature dependent rate coefficients are best fit by the Arrhenius expressions k(camphene + OH) = (4.1 ± 1.2) × 10-12 exp ((754 ± 44)/T) for OH reaction and k(O3 + camphene) = (7.6 ± 1.2) × 10-18 exp ((-805 ± 51)/T) for O3 reaction. Additionally, product studies have been performed at (298 ± 2) K and 760 Torr of synthetic air for the OH reactions in the absence and presence of NOx, and for O3 molecules at (298 ± 2) K and 750 Torr of synthetic air. For OH reaction the obtained molar products yields were: acetone (10 ± 2) % and (33 ± 6) %, and formaldehyde (3.6 ± 0.7) % and (10 ± 2) % in the absence and presence of NOx, respectively. Formaldehyde was the unique product quantified due to O3 reaction obtaining a yield of (29 ± 6) %. The work has shown that the reaction of OH with camphene in polluted environment is a relevant source of acetone and that it also contributes with formaldehyde and other carbonyl compounds. Moreover, the ozonolysis of camphene is a source of formaldehyde and other oxygenated compounds determined previously by Jay and Stieglitz (1987, 1989) and Hakola et al. (1994). Acetone and formaldehyde are sources of HOx radicals and acetone is also a source of peroxy acetyl nitrate (PAN) (McKeen et al. 1997; Müller and Brasseur 1999; Fischer et al. 2014). According to some field measurements of biogenic compounds, isoprene is major source for formaldehyde and acetone formation. Although, some studies have been suggested monoterpenes also contribute to the formation of these carbonyl compounds (Goldstein and Schade 2000; Kesselmeier et al. 2000). In addition, monoterpenes have impact on SOA formation (Kanakidou et al. 2004; Russell et al. 2011; Kahnt et al. 2014).