Measurements of photo-oxidation products from the reaction of a series of alkyl-benzenes with hydroxyl radicals during EXACT using comprehensive gas chromatography

Photo-oxidation products from the reaction of a series of alkyl-benzenes, (benzene, toluene, p-xylene and 1,3,5-trimethyl-benzene) with hydroxyl radicals in the presence of NOx have been investigated using comprehensive gas chromatography (GCXGC). A GCXGC system has been developed which utilises valve modulation and independent 5 separations as a function of both volatility and polarity. A number of carbonyl-type compounds were identified during a series of reactions carried out at the European Photoreactor (EUPHORE), a large volume outdoor reaction chamber in Valencia, Spain. Two litre chamber air samples were cryo-focused, with a sampling frequency of 30ṁin, allowing the evolution of species to be followed over oxidation periods of 3–6 h. To facil10 itate product identification, several carbonyl compounds, which were possible products of the photo-oxidation, were synthesised and used as reference standards. For toluene reactions, observed oxygenated intermediates found included the coeluting pair α-angelicalactone/4-oxo-2-pentenal, maleic anhydride, citraconic anhydride, benzaldehyde and p-methyl benzoquinone. In the p-xylene experiment, the 15 products identified were E/Z-hex-3-en-2,5-dione and citraconic anhydride. For 1,3,5TMB reactions, the products identified were 3,5-dimethylbenzaldehyde, 3,5-dimethyl3H-furan-2-one and 3-methyl-5-methylene-5H-furan-2-one. Preliminary quantification was carried out on identified compounds using liquid standards. Comparison of FTIR and GCXGC for the measurement of the parent aromatics generally showed good 20 agreement.