Measurements of photo-oxidation products from the reaction of a series of alkyl-benzenes with hydroxyl radicals during EXACT using comprehensive gas chromatography J. F. Hamilton1, A. C. Lewis2, C. Bloss1, V. Wagner1, A. P. Henderson3, B. T. Golding3, K. Wirtz4, M. Martin-Reviejo4, and M. J. Pilling1 1University of Leeds, Department of Chemistry, Woodhouse Lane, Leeds, LS2 9JT, UK 2University of York, Department of Chemistry, Heslington, York, YO10 5DD, UK 3School of Natural Sciences – Chemistry, Bedson Building, University of Newcastle upon Tyne, Newcastle upon Tyne NEI 7RU, UK 4Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM), EUPHORE laboratories, C/Charles Darwin, 14-Parc Technológico, Paterna, Valencia, Spain
Abstract. 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 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 (Effects of
the oXidation of Aromatic Compounds in the Troposphere). 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.
For toluene reactions, observed oxygenated intermediates found included the
co-eluting pair a-angelicalactone/4-oxo-2-pentenal, maleic anhydride, citraconic
anhydride, benzaldehyde and p-methyl benzoquinone. In the p-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.
Citation: Hamilton, J. F., Lewis, A. C., Bloss, C., Wagner, V., Henderson, A. P., Golding, B. T., Wirtz, K., Martin-Reviejo, M., and Pilling, M. J.: Measurements of photo-oxidation products from the reaction of a series of alkyl-benzenes with hydroxyl radicals during EXACT using comprehensive gas chromatography, Atmos. Chem. Phys., 3, 1999-2014, doi:10.5194/acp-3-1999-2003, 2003.