Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 2255-2272, 2016
https://doi.org/10.5194/acp-16-2255-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Feb 2016
Role of methyl group number on SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions
L. Li1,2, P. Tang1,2, S. Nakao1,2,a, C.-L. Chen1,2,b, and D. R. Cocker III1,2 1University of California, Riverside, Department of Chemical and Environmental Engineering, Riverside, CA 92507, USA
2College of Engineering-Center for Environmental Research and Technology (CE-CERT), Riverside, CA 92507, USA
acurrently at: Clarkson University, Department of Chemical and Biomolecular Engineering, Potsdam, NY 13699, USA
bcurrently at: Scripps Institution of Oceanography, University of California, La Jolla, CA, USA
Abstract. Substitution of methyl groups onto the aromatic ring determines the secondary organic aerosol (SOA) formation from the monocyclic aromatic hydrocarbon precursor (SOA yield and chemical composition). This study links the number of methyl groups on the aromatic ring to SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions (HC/NO  >  10 ppbC : ppb). Monocyclic aromatic hydrocarbons with increasing numbers of methyl groups are systematically studied. SOA formation from pentamethylbenzene and hexamethylbenzene are reported for the first time. A decreasing SOA yield with increasing number of methyl groups is observed. Linear trends are found in both f44 vs. f43 and O / C vs. H / C for SOA from monocyclic aromatic hydrocarbons with zero to six methyl groups. An SOA oxidation state predictive method based on benzene is used to examine the effect of added methyl groups on aromatic oxidation under low-NOx conditions. Further, the impact of methyl group number on density and volatility of SOA from monocyclic aromatic hydrocarbons is explored. Finally, a mechanism for methyl group impact on SOA formation is suggested. Overall, this work suggests that, as more methyl groups are attached on the aromatic ring, SOA products from these monocyclic aromatic hydrocarbons become less oxidized per mass/carbon on the basis of SOA yield or chemical composition.

Citation: Li, L., Tang, P., Nakao, S., Chen, C.-L., and Cocker III, D. R.: Role of methyl group number on SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions, Atmos. Chem. Phys., 16, 2255-2272, https://doi.org/10.5194/acp-16-2255-2016, 2016.
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Short summary
Substitution of methyl groups onto the aromatic ring determines the SOA formation from the aromatic hydrocarbon precursor. This study links the number of methyl groups on the aromatic ring to SOA formation from aromatic hydrocarbons photooxidation under low-NOx conditions (HC / NO > 10 ppbC : ppb). Aromatics are determined to be less oxidized per mass/carbon as the number of methyl groups on aromatic ring increases based on SOA yield, SOA chemical composition and SOA physical characteristics.
Substitution of methyl groups onto the aromatic ring determines the SOA formation from the...
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