PRIMARY PRODUCT DISTRIBUTION FROM THE REACTION OF HYDROXYL RADICALS WITH TOLUENE AT PPB NOX MIXING RATIOS

A study has been conducted to examine the OH-initiated degradation pro ducts of toluene in the presence of sub part-per-million levels of NOx . The experiments were conducted in a dynamic reactor to minimize the conversion of the aromatic compounds while allowing a sufficient mass of products to be collected for analysis. The major primary products d etected in the toluene system (with molar yields) include glyoxal (0.2 38), methylglyoxal (0.167), o-cresol (0.120), benzaldehyde (0.06), 4-o xo-2-pentenal (0.03), and p-cresol (0.03). Six other reaction products , most being ring cleavage products, were measured at yields below 3%. Corrections for secondary OH reactions with the products were made wh ere necessary. The formation of the cresol isomers was found to be inv ariant to the NO2 concentrations which indicates that under atmospheri c conditions the initial hydroxycyclohexadienyl radical reaction with NO2 is a minor process and that most of the reaction occurs with O-2. The product yields found in this study are expected to be representati ve of those that occur in the urban atmosphere at ambient NO2 concentr ations.