RESUMO
The pseudo-first-order loss of coniferyl aldehyde, adsorbed on silicon dioxide particles, upon heterogeneous ozonolysis was monitored at various ozone mixing ratios in the absence and presence of simulated sunlight. For the first time we investigated the effect of light on the heterogeneous ozonolysis of coniferyl aldehyde adsorbed on silica particles. We found that UV-VIS light (λ>300 nm) does not impact the degradation of coniferyl aldehyde by ozone but induces an additional, slow photolysis of the aldehyde with a photolytic rate constant of ~10(-5) s(-1). In both cases, that is, in presence and/or absence of light, the heterogeneous ozonation kinetics are well described by an immediate gas-surface reaction formalism with light-independent rate constants of k(2nd)=(7.2±0.9)×10(-19) cm(3) molec(-1) s(-1) and (7.6±1.7)×10(-19) cm(3) molec(-1) s(-1) in the absence and presence of light, respectively. Five oxidation products: glycolic acid, oxalic acid, vanillin, vanillic acid and 3,4-dihydroxybenzoic acid were identified and confirmed by their corresponding standards. Vanillin and vanillic acid absorb light in the region λ>300 nm and thus can further participate in the direct and indirect photolysis processes of atmospheric relevance. A reaction mechanism is proposed in order to elucidate the ozonolysis reaction and to explain the reaction products.