Light-induced heterogeneous ozone processing on organic coated particles: Kinetics and condensed-phase products

For the first time we investigated the effect of solar irradiation upon the heterogeneous ozonation of adsorbed 3,4,5-trimethoxybenzaldehyde on solid surface. Light-induced heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde adsorbed on silica particles were performed and the consecutive reaction products were identified. At an ozone mixing ratio of 250 ppb, the loss of 3,4,5-trimethoxybenzaldehyde ranged from 1.0 . 10(-6) s(-1) in the dark to 2.9 . 10(-5) s(-1) under light irradiation. Such large enhancement of 29 times clearly shows the importance of light (lambda > 300 nm) during the heterogeneous ozonolysis on organic coated particles. The reaction products identified in this study (3,4,5-trimethoxybenzoic acid, syringic acid, methyl 3,4,5-trimethoxybenzoate) absorb light in the spectral window (lambda > 300 nm) which implies that light-induced heterogeneous ozone processing can have an influence on the aerosol surfaces by changing their physico-chemical properties. The main identified product of the heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde under dark conditions and in presence of light was 3,4,5-trimethoxybenzoic acid. For this reason we estimated the carbon yield of 3,4,5-trimethoxybenzoic acid. Carbon yields of 3,4,5-trimethoxybenzoic acid decreased with increasing ozone mixing ratio; from 40% at 250 ppb to 15% at >= 2.5 ppm under dark conditions. At ozone mixing ratio (250 ppb-1 ppm), carbon yields of 3,4,5-trimethoxybenzaldehyde are relatively higher in the experiment under dark condition than under simulated solar light. (C) 2010 Elsevier Ltd. All rights reserved.