ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-3-1999-2003 Measurements of photo-oxidation products from the reaction of a series of alkyl-benzenes with hydroxyl radicals during EXACT using comprehensive gas chromatography Hamilton J. F. 1 Lewis A. C. 2 Bloss C. 1 Wagner V. 1 Henderson A. P. 3 Golding B. T. 3 Wirtz K. 4 Martin-Reviejo M. 4 Pilling M. J. 1 University of Leeds, Department of Chemistry, Woodhouse Lane, Leeds, LS2 9JT, UK University of York, Department of Chemistry, Heslington, York, YO10 5DD, UK School of Natural Sciences – Chemistry, Bedson Building, University of Newcastle upon Tyne, Newcastle upon Tyne NEI 7RU, UK Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM), EUPHORE laboratories, C/Charles Darwin, 14-Parc Technológico, Paterna, Valencia, Spain 13 11 2003 3 6 1999 2014 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/3/1999/2003/acp-3-1999-2003.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/3/1999/2003/acp-3-1999-2003.pdf

Photo-oxidation products from the reaction of a series of alkyl-benzenes, (benzene, toluene, <i>p</i>-xylene and 1,3,5-trimethyl-benzene) with hydroxyl radicals in the presence of NO<sub>x</sub> have been investigated using comprehensive gas chromatography (GCxGC). A GCxGC system has been developed which utilises valve modulation and independent 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. Experiments were carried as part of the EXACT project (<b>E</b>ffects of the o<b>X</b>idation of <b>A</b>romatic <b>C</b>ompounds in the <b>T</b>roposphere). Two litre chamber air samples were cryo-focused, with a sampling frequency of 30 minutes, allowing the evolution of species to be followed over oxidation periods of 3-6 hours. To facilitate product identification, several carbonyl compounds, which were possible products of the photo-oxidation, were synthesised and used as reference standards.<br> <br> For toluene reactions, observed oxygenated intermediates found included the co-eluting pair <font face="Symbol">a</font>-angelicalactone/4-oxo-2-pentenal, maleic anhydride, citraconic anhydride, benzaldehyde and <i>p</i>-methyl benzoquinone. In the <i>p</i>-xylene experiment, the products identified were E/Z-hex-3-en-2,5-dione and citraconic anhydride. For 1,3,5-TMB reactions, the products identified were 3,5-dimethylbenzaldehyde, 3,5-dimethyl-3H-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 agreement. Comparison of the concentrations observed by GCxGC to concentration-time profiles simulated using the Master Chemical Mechanism, MCMv3, demonstrates that this mechanism significantly over-predicts the concentrations of many product compounds and highlights the uncertainties which exist in our understanding of the atmospheric oxidation of aromatics.