Abstract

Hydroxyl radical (OH) oxidation of toluene produces ring-retaining products: cresol and benzaldehyde, and ring-opening products: bicyclic intermediate compounds and epoxides. Here, first- and later-generation OH oxidation products from cresol and benzaldehyde are identified in laboratory chamber ... Show moreHydroxyl radical (OH) oxidation of toluene produces ring-retaining products: cresol and benzaldehyde, and ring-opening products: bicyclic intermediate compounds and epoxides. Here, first- and later-generation OH oxidation products from cresol and benzaldehyde are identified in laboratory chamber experiments. For benzaldehyde, first- generation ring-retaining products are identified, but later-eneration products are not detected. For cresol, low-volatility (saturation mass concentration, C * similar to 3.5 x 10(4) -7.7 x 10(-3) mu gm(-3)), first- and later-generation ring-retaining products are identified. Subsequent OH addition to the aromatic ring of o-cresol leads to compounds such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones and dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes. These products are detected in the gas phase by chemical ionization mass spectrometry (CIMS) and in the particle phase using offline direct analysis in real-time mass spectrometry (DART-MS). Our data suggest that the yield of trihydroxy toluene from dihydroxy toluene is substantial. While an exact yield cannot be reported as authentic standards are unavailable, we find that a yield for trihydroxy toluene from dihydroxy toluene of similar to 0.7 (equal to the reported yield of dihydroxy toluene from o-cresol (Olariu et al., idation under low-NO conditions. These results suggest that even though the cresol pathway accounts for only similar to 20% of the oxidation products of toluene, it is the source of a significant fraction (similar to 20-40 %) of toluene secondary organic aerosol (SOA) due to the formation of low- volatility products. Show less