Gas-phase ozonolysis of β-ocimene: Temperature dependent rate coefficients and product distribution

Publication date: December 2016
Source:Atmospheric Environment, Volume 147
Author(s): Elizabeth Gaona-Colmán, María B. Blanco, Ian Barnes, Mariano A. Teruel
Rate coefficients for the reaction of β-ocimene with O3 molecules have been determined over the temperature range 288–311 K at 750 Torr total pressure of nitrogen using the relative rate technique. The investigations were performed in a large volume reaction vessel using long-path in-situ Fourier transformed infrared (FTIR) spectroscopy to monitor the reactants and products. A value of k(β-ocimene + O3) = (3.74 ± 0.92) × 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹ has been obtained for the reaction at 298 K. The temperature dependence of the reaction is best described by the Arrhenius expression k = (1.94 ± 0.02) × 10⁻¹⁴ exp [(−1181 ± 51)/T] cm³ molecule⁻¹ s⁻¹. In addition, a product study has been carried out at 298 K in 750 Torr of synthetic air and the following products with yields in molar % were observed: formaldehyde (36 ± 2), acetone (15 ± 1), methylglyoxal (9.5 ± 0.4) and hydroxyacetone (19 ± 1). The formation of formaldehyde can be explained by the addition of O3 to the C1C2 double bond of the β-ocimene. Addition of O3 to the C6C7 double bond leads to the formation of acetone and the CH3C·(OO·)CH3 biradical, which can through isomerization/stabilization form methylglyoxal (hydroperoxide channel) and hydroxyacetone. The formed products will contribute to the formation of PAN and derivatives in polluted environments and also the oxidation capacity of the atmosphere.

Graphical abstract

http://ift.tt/2dJdGzI