Article pubs.acs.org/JPCA
Rate Coefficients for the Gas-Phase Reaction of Chlorine Atoms with a Series of Methoxylated Aromatic Compounds Amélie Lauraguais,†,‡,§ Iustinian Bejan,†,∥ Ian Barnes,† Peter Wiesen,† Cécile Coeur-Tourneur,*,‡,§ and Andy Cassez‡,§ †
Faculty C-Department of Physical Chemistry, University of Wuppertal, Gauss Strasse 20, D-42119 Wuppertal, Germany Laboratoire de Physico-Chimie de l’Atmosphère (LPCA), EA 4493, Université du Littoral Côte d’Opale, 32 Avenue Foch, 62930 Wimereux, France § Université Lille Nord de France, Lille, France ‡
ABSTRACT: The reaction of a series of oxygenated aromatics (two methoxybenzene and six methoxyphenol isomers) with chlorine atoms has been studied in two simulation chambers with volumes of 1080 and 480 L at the University of Wuppertal. Experiments were performed at 295 ± 2 K and a total pressure of synthetic air of 1 bar using the relative kinetic method with in situ Fourier transform infrared spectroscopy for chemical analysis. The following rate coefficients (in units of cubic centimeter per molecule per second) were determined: (1.07 ± 0.24) × 10−10 for methoxybenzene, (1.20 ± 0.24) × 10−10 for 1-methoxy-2-methylbenzene, (2.97 ± 0.66) × 10−10 for 2-methoxyphenol (guaiacol), (2.99 ± 0.62) × 10−10 for 3-methoxyphenol, (2.86 ± 0.58) × 10−10 for 4-methoxyphenol, (3.35 ± 0.68) × 10−10 for 2methoxy-4-methylphenol, (4.73 ± 1.06) × 10−10 for 2,3-dimethoxyphenol, and (2.71 ± 0.61) × 10−10 for 2,6-dimethoxyphenol (syringol). To the best of our knowledge, this work represents the first determination of the rate coefficients for the gas-phase reaction of the chlorine atoms with the methoxy-aromatic compounds investigated. The reactivity of the methoxylated aromatics toward Cl is compared with that of other substituted aromatic compounds, and the differences in the rate coefficients are interpreted in terms of the type, number, and position of the different substituents on the aromatic ring. The atmospheric implications of the studied reactions are also discussed.
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INTRODUCTION In urban areas, ∼20% of non-methane hydrocarbons are aromatics, and their contribution to air pollution is well recognized today.1 They are known to form photooxidants2,3 and secondary organic aerosols (SOA)1,4,5 and to present risks for human health.6 The current emergence of environmental policies and the imminent depletion of fossil fuels are prompting a change to renewable energy sources. The combustion of biomass represents an energy source that can reduce the world’s dependence on fossil fuels. However, it has been observed that biomass burning is an important source of atmospheric aerosols. This pollution has significant impacts on human health,7 regional and global air quality,8 and climate.9,10 Biomass burning includes natural fires, human-initiated burning of vegetation, and residential wood combustion.11−15 The pyrolysis of wood lignin produces methoxyphenols [2methoxyphenol (guaiacol) and 2,6-dimethoxyphenol (syringol) and their derivatives].11−16 These oxygenated aromatics are then partitioned between gas and particle phases, and recent studies have shown their high reactivity with OH radicals17,18 and their potential to form SOA.18,19 Rate coefficients for the reaction of organics with Cl atoms are generally 10 times higher than those of the corresponding © 2014 American Chemical Society
OH reactions. However, because the global atmospheric chlorine atom concentration is
