Atmospheric Oxidation of Toluene in a Large-Volume Outdoor Photoreactor:  In Situ Determination of Ring-Retaining Product Yields

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 1998-12, Vol.102 (50), p.10289-10299
• Main Authors: Klotz, Björn, Sørensen, Søren, Barnes, Ian, Becker, Karl H, Etzkorn, Thomas, Volkamer, Rainer, Platt, Ulrich, Wirtz, Klaus, Martín-Reviejo, Montserrat
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp982719n

Experiments on the photooxidation of toluene/NO x /air mixtures were performed in the European Photoreactor (EUPHORE), a large-scale outdoor reaction chamber located in Valencia/Spain. The objective of the study was the in situ determination of the yields of ring-retaining products by differential optical absorption spectroscopy (DOAS) and the elucidation of their formation pathways. The experiments were performed with toluene concentrations between 0.68 and 3.85 ppm and initial NO x concentrations ranging from 3 to 300 ppb, i.e., down to the range actually observed in the lower atmosphere. The ring-retaining product yields were found to be 5.8 ± 0.8%, 12.0 ± 1.4%, 2.7 ± 0.7%, and 3.2 ± 0.6% for benzaldehyde, o-cresol, m-cresol, and p-cresol, respectively. Under the experimental conditions, no dependency of the yields on the NO x concentration or the toluene/NO x ratio could be found. The formation kinetics of the cresols are in line with a “prompt” formation mechanism, i.e., abstraction of a hydrogen atom from the toluene−OH adduct (toluene−OH + O2 → cresols + HO2). In addition, substantial evidence was found that reaction with NO3 radicals represents an important sink for cresols in smog chamber studies conducted under conditions of NO x concentrations above the range observed in the troposphere, possibly also under tropospheric conditions.