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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1167
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Feb 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
High-molecular-weight esters in α-pinene ozonolysis secondary organic aerosol: Structural characterization and mechanistic proposal for their formation from highly oxygenated molecules
Ariane Kahnt1,a, Reinhilde Vermeylen1,b, Yoshiteru Iinuma2,c, Mohammad Safi Shalamzari1,d, Willy Maenhaut3, and Magda Claeys1 1Department of Pharmaceutical Sciences, University of Antwerp (Campus Drie Eiken), 2610, Antwerp, Belgium
2Leibniz-Institut für Troposphärenforschung (TROPOS), Permoserstr. 15, 04318 Leipzig, Germany
3Department of Chemistry, Ghent University, Krijgslaan 281, S12, 9000 Ghent, Belgium
anow at: Development Bioanalysis, Janssen R&D, Turnhoutseweg 30, 2340 Beerse, Belgium
bnow at: Soil Service of Belgium, W. de Croylaan 48, Heverlee, Belgium
cnow at: Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Kunigami, Okinawa 904-0495, Japan
dnow at: Dr. Reddy's Laboratories Ltd., Zernikedreef 12, 2333 CL Leiden, the Netherlands
Abstract. Stable high-molecular-weight esters are present in α-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a diaterpenylic ester of cis-pinic acid with a molecular weight (MW) of 368 C19H28O7) and a hydroxypinonyl ester of cis-pinic acid with a MW of 358 (C17H26O8). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on high-molecular-weight esters present in α-pinene/O3 SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW 368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW 358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C19H28O11 product, which is detected as a major species in α-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization – atmospheric pressure ionization – time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012, 2014). It is suggested that an acyl peroxy radical related to cis-pinic acid (RO2·) and an alkoxy radical related to 7- or 5-hydroxypinonic acid (R'O·) serve as key gas-phase radicals and combine according to a RO2· + R'O· → RO3R' radical termination reaction. Subsequently, the unstable C19H28O1119H28O7 (MW 368) and C17H26O8 (MW 358), respectively. The proposed mechanism is supported by several observations reported in the literature. On the basis of the indirect evidence presented in this study, we hypothesize that RO2· + R'O· → RO3R; chemistry is at the underlying molecular basis of high-molecular-weight ester formation upon α-pinene ozonolysis and may thus be of importance for new particle formation and growth in pristine forested environments.
Citation: Kahnt, A., Vermeylen, R., Iinuma, Y., Safi Shalamzari, M., Maenhaut, W., and Claeys, M.: High-molecular-weight esters in α-pinene ozonolysis secondary organic aerosol: Structural characterization and mechanistic proposal for their formation from highly oxygenated molecules, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1167, in review, 2018.
Ariane Kahnt et al.
Ariane Kahnt et al.
Ariane Kahnt et al.

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Short summary
High-molecular-weight esters present in α-pinene ozonolysis secondary organic aerosol have been structurally characterized with electrospray ionization mass spectrometry. Unambiguous evidence could be obtained for the linkage in the MW 368 hydroxypinonyl ester of pinic acid, while the same linkage could be supported for the MW 358 diaterpenylic ester of pinic acid. A mechanistic proposal is presented to explain their possible formation from highly oxygenated molecules reported in previous work.
High-molecular-weight esters present in α-pinene ozonolysis secondary organic aerosol have been...
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