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

Abstract

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 NO x have been investigated using comprehensive gas chromatography (GC×GC). A GC×GC 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 α-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 GC×GC for the measurement of the parent aroCorrespondence to: J. F. Hamilton (jacquih@chemistry.leeds.ac.uk) matics generally showed good agreement. Comparison of the concentrations observed by GC×GC to concentrationtime 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.

A quantification method for heat-decomposable methylglyoxal oligomers and its application on 1,3,5-trimethylbenzene SOA

“…Methylglyoxal is reported in the literature as an important oxidation product of 1,3,5-TMB Healy et al, 2008;Cocker et al, 2001;Wyche et al, 2009;Rickard et al, 2010;Kalberer et al, 2004;Yu et al, 1997;Kleindienst et al, 1999;Müller et al, 2012;Nishino et al, 2010;Hamilton et al, 2003;Tuazon et al, 1986;Bandow and Washida, 1985), with yields in the particle phase between 0.7 and 2 %.…”

“…Huang et al, 2015;Kalberer et al, 2004Kalberer et al, , 2006Paulsen et al, 2005;Healy et al, 2008;Cocker et al, 2001;Metzger et al, 2008;Wyche et al, 2009;Yu et al, 1997). Methylglyoxal was found as one of the most important oxidation product Healy et al, 2008;Cocker et al, 2001;Wyche et al, 2009;Rickard et al, 2010;Kalberer et al, 2004;Yu et al, 1997;Müller et al, 2012;Nishino et al, 2010;Hamilton et al, 2003;Tuazon et al, 1986;Bandow and Washida, 1985;Lim and Turpin, 2015) contributing with a fraction of up to 2 % to the particle mass (Healy et al, 2008;Cocker et al, 2001). Methylglyoxal has often been described to form oligomeric compounds in the aqueous particle phase (see, e.g., Herrmann et al, 2015, for an overview;De Haan et al, 2009;Kalberer et al, 2004;Loeffler et al, 2006;Zhao et al, 2006;Sareen et al, 2010;Altieri et al, 2008), which are supposed to play an important role in the formation of aqueous secondary organic aerosols (aqSOA; e.g.…”

Evaluation of detailed aromatic mechanisms (MCMv3 and MCMv3.1) against environmental chamber data

“…Sampling ports in the floor panels connect to various instruments via PTFE Teflon lines: an ozone monitor (Monitor Labs), two NO x monitors (ML9841A and Eco physics CLD770 AL), a hygrometer, GC-FID/ECD (HP6890) for measuring PAN and VOC concentrations, and GC-Schmitt PAN Analyser for PAN and methylglyoxal. During the EX-ACT campaigns an additional instrument was used for comprehensive gas chromatography (GCXGC) and measured carbonyl compounds (Hamilton et al, 2003).…”

“…These measurements and their comparison with MCM simulations have been discussed by Hamilton et al (2003). In the toluene experiments, observed products included α-angelica lactone/4-oxo-2-pentenal as a co-eluting pair, maleic-anhydride and methyl-maleic-anhydride.…”

The production and persistence of ΣRONO<sub>2</sub> in the Mexico City plume

“…In addition to uncertainty in the yield of nitrates from the initial oxidation of aromatic compounds, there is a high degree of uncertainty in the yields of ring-opening vs. ring-retaining products (Hamilton et al, 2003;Jenkin et al, 2003;Wagner et al, 2003;Wyche et al, 2009). The products of ringopening pathways could themselves have high nitrate yields and significant nitrate formation could thus result from oxidation of the first-generation products of aromatic oxidation.…”