ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-7301-2011 Secondary organic aerosol formation from the photooxidation of isoprene, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene under high NO<sub>x</sub> conditions Sato K. 1 2 4 Nakao S. 1 3 Clark C. H. 1 3 Qi L. 1 3 Cocker III D. R. 1 3 Bourns College of Engineering – Center for Environmental Research & Technology, University of California, Riverside, 1084 Columbia Ave., Riverside, CA 92507, USA Asian Environment Research Group, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki, 305-8506, Japan Department of Chemical and Environmental Engineering, University of California, Riverside, CA 92521, USA now at: Center for Regional Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki, 305-8506, Japan 25 07 2011 11 14 7301 7317 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/7301/2011/acp-11-7301-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/7301/2011/acp-11-7301-2011.pdf

Secondary organic aerosol (SOA) formation from atmospheric oxidation of isoprene has been the subject of multiple studies in recent years; however, reactions of other conjugated dienes emitted from anthropogenic sources remain poorly understood. SOA formation from the photooxidation of isoprene, isoprene-1-<sup>13</sup>C, 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene is investigated for high NO<sub>x</sub> conditions. The SOA yield measured in the 1,3-butadiene/NO<sub>x</sub>/H<sub>2</sub>O<sub>2</sub> irradiation system (0.089–0.178) was close to or slightly higher than that measured with isoprene under similar NO<sub>x</sub> conditions (0.077–0.103), suggesting that the photooxidation of 1,3-butadiene is a possible source of SOA in urban air. In contrast, a very small amount of SOA particles was produced in experiments with 2,3-dimethyl-1,3-butadiene. Off-line liquid chromatography – mass spectrometry analysis revealed that the signals of oligoesters comprise a major fraction (0.10–0.33) of the signals of the SOA products observed from all dienes investigated. The oligoesters originate from the unsaturated aldehyde gas phase diene reaction products; namely, semi-volatile compounds produced by the oxidation of the unsaturated aldehyde undergo particle-phase oligoester formation. Oligoesters produced by the dehydration reaction between nitrooxypolyol and 2-methylglyceric acid monomer or its oligomer were also characterized in these experiments with isoprene as the starting diene. These oligomers are possible sources of the 2-methyltetrols found in ambient aerosol samples collected under high NO<sub>x</sub> conditions. Furthermore, in low-temperature experiments also conducted in this study, the SOA yield measured with isoprene at 278 K was 2–3 times as high as that measured at 300 K under similar concentration conditions. Although oligomerization plays an important role in SOA formation from isoprene photooxidation, the observed temperature dependence of SOA yield is largely explained by gas/particle partitioning of semi-volatile compounds.

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