New results on the atmospheric photooxidation of simple alkylbenzenes Original Research Article

A study of the photolysis of two postulated intermediates in the OH initiated photooxidation of aromatic hydrocarbons, benzene oxide/oxepin and toluene-1,2-oxide/2-methyloxepin, has been conducted under the real light conditions of a large volume outdoor reaction chamber. The main focus of the study was on the formation of the hydroxylated aromatic hydrocarbons, i.e., phenol from benzene oxide/oxepin and the cresol isomers from toluene-1,2-oxide/2-methyloxepin. Photolysis frequencies were measured relative to that of NO2, which was determined with a filter radiometer. A linear dependency was found within the experimental errors, the ratios of the photolysis frequencies of the arene oxides to that of NO2 were found to be (4.41±0.44)·10−2 and (3.99±0.48)·10−2 for benzene oxide/oxepin and toluene-1,2-oxide/2-methyloxepin, respectively. The yield of phenol in the photolysis of benzene oxide/oxepin was found to be (43.2±4.5)%, independent of the light intensity. For toluene-1,2-oxide/2-methyloxepin, an o-cresol yield of (2.7±2.2)% was determined, the formation of other cresol isomers was not observed. The results obtained are in agreement with arene oxides being intermediates in the atmospheric photooxidation of benzene and toluene, they are discussed with regard to their implications for the formation of hydroxylated aromatics in the OH initiated photooxidation of benzene and toluene.