NEW RESULTS ON THE ATMOSPHERIC PHOTOOXIDATION OF SIMPLE ALKYLBENZENES

A study of the photolysis of two postulated intermediates in the OH in itiated photooxidation of aromatic hydrocarbons, benzene oxide/oxepin and toluene-l,2-oxide/2-methyloxepin, has been conducted under the rea l light conditions of a large volume outdoor reaction chamber. The mai n focus of the study was on the formation of the hydroxylated aromatic hydrocarbons, i.e., phel from benzene oxide/oxepin and the cresol iso mers from toluene-l,2-oxide/2-methyloxepin. Photolysis frequencies wer e measured relative to that of NO2, which was determined with a filter radiometer, A linear dependency was found within the experimental err ors, the ratios of the photolysis frequencies of the arene oxides to t hat 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-l,2-oxide/2-methyloxepi n, respectively. The yield of phenol in the photolysis of benzene oxid e/oxepin was found to be (43.2 +/- 4.5)%, independent of the light int ensity. For toluene-1,2-oxide/2-methyloxepin, an o-cresol yield of (2. 7 i:2.2)Clo was determined, the formation of other cresol isomers was not observed.The results obtained are in agreement with arene oxides b eing intermediates in the atmospheric photooxidation of benzene and to luene, they are discussed with regard to their implications for the fo rmation of hydroxylated aromatics in the OH initiated photooxidation o f benzene and toluene. (C) 1998 Elsevier Science B.V. All rights reser ved.