Atmospheric chemistry of benzene oxide oxepin

The atmospheric chemistry of benzene oxide/oxepin, a possible intermediate in the atmospheric oxidation of aromatic hydrocarbons, has been investigated in a large volume photoreactor at 298 K and atmospheric pressure using in situ FTIR spectroscopy for the analysis. Rate coefficients of (10.0 +/- 0.4) x 10(-11) and (9.2 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1) have been determined for the reaction of benzene oxide/oxepin with OH and NO3 radicals, respectively. Reaction with OH radicals produces almost exclusively the (E,Z)- and (E,E)-isomers of hexa-2,4-dienedial, whereas reaction with NO3 produces (Z,Z)-hexa-2,4-dienedial and unidentified organic nitrates. Phenol has been observed as a major product of the thermal decomposition, visible and UV photolysis of benzene oxide/oxepin. The results are discussed in conjunction with the oxidation mechanisms of aromatic hydrocarbons. The major atmospheric sinks of benzene oxide/oxepin will be reaction with OH radicals and photolysis and, under smog chamber conditions with high NO2 concentrations, also reaction with NO3.