1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
2Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
3Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California 91125, USA
4Current Affiliation: National Center for Atmospheric Research, Boulder, Colorado, USA
5Current Affiliation: Chemistry and Firearms Branch, US Army Criminal Investigation Laboratory, Forest Park, Georgia, USA
6Current Affiliation: Cooperative Institute for Research in Environmental Science and National Oceanic and Atmospheric Administration, Boulder, Colorado, USA
7Current Affiliation: South Coast Air Quality Management District, Diamond Bar, California, USA
Received: 04 Oct 2016 – Discussion started: 10 Oct 2016
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 experiments. For benzaldehyde, first-generation ring-retaining products are identified, but later-generation products are not detected. For cresol, low-volatility (saturation mass concentration, C* ∼ 3.5 × 104 − 7.7 × 10−3 µg m−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 ∼ 0.7 (equal to the reported yield of dihydroxy toluene from o-cresol; Olariu et al., 2002) is consistent with experimental results for o-cresol oxidation under low-NO conditions. These results suggest that even though the cresol pathway accounts for only ∼ 20 % of the oxidation products of toluene, it is the source of a significant fraction (∼ 20–40 %) of toluene secondary organic aerosol (SOA) due to the formation of low-volatility products.
Revised: 23 Jan 2017 – Accepted: 15 Feb 2017 – Published: 10 Mar 2017
Schwantes, R. H., Schilling, K. A., McVay, R. C., Lignell, H., Coggon, M. M., Zhang, X., Wennberg, P. O., and Seinfeld, J. H.: Formation of highly oxygenated low-volatility products from cresol oxidation, Atmos. Chem. Phys., 17, 3453-3474, doi:10.5194/acp-17-3453-2017, 2017.