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Published March 10, 2017 | Supplemental Material + Published
Journal Article Open

Formation of highly oxygenated low-volatility products from cresol oxidation


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  ×  10^4 − 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.

Additional Information

© Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 04 Oct 2016 – Discussion started: 10 Oct 2016. Revised: 23 Jan 2017 – Accepted: 15 Feb 2017 – Published: 10 Mar 2017. Data availability: Data used within this work are available upon request. Please email Rebecca Schwantes (rschwant@ucar.edu). The Supplement related to this article is available online at doi:10.5194/acp-17-3453-2017-supplement. This work was supported by National Science Foundation grants AGS-1240604 and AGS-1523500. We thank Hannah Allen and Anke Noelscher for their experimental assistance and Nathan Dalleska and John Crounse for helpful discussions. The National Center for Atmospheric Research is sponsored by the National Science Foundation. Edited by: Y. Rudich. Reviewed by: H. Herrmann and T. Mentel. The authors declare that they have no conflict of interest.

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Supplemental Material - acp-17-3453-2017-supplement.pdf


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