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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Dec 2018

Research article | 19 Dec 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Effect of temperature on the formation of Highly-oxygenated Organic Molecules (HOM) from alpha-pinene ozonolysis

Lauriane L. J. Quéléver1, Kasper Kristensen2,a, Louise Jensen2, Bernadette Rosati2,3, Ricky Teiwes2,3, Kaspar R. Daellenbach1, Otso Peräkylä1, Pontus Roldin4, Henrik B. Pedersen3, Marianne Glasius2, Merete Bilde2, and Mikael Ehn1 Lauriane L. J. Quéléver et al.
  • 1Institute for Atmospheric and Earth System Research – INAR/Physics , P.O. Box 64, 00014 University of Helsinki, Finland
  • 2Aarhus University, Department of Chemistry, Langelandsgade 140, 8000 Aarhus C, Denmark
  • 3Aarhus University, Department of Physics and Astronomy, Ny Munkegade 120, 8000 Aarhus C, Denmark
  • 4Lund University, Division of Nuclear Physics, P.O. Box 118, 22100 Lund, Sweden
  • anow at: University of California, Department of Environmental Science, Policy and Management, Hilgard Hall 251B, CA-94720-3114 Berkeley, United States of America

Abstract. Highly-oxygenated Organic Molecules (HOM) are important contributors to Secondary Organic Aerosol (SOA) and New-Particle Formation (NPF) in the boreal atmosphere. This newly discovered class of molecules is efficiently formed from atmospheric oxidation of biogenic volatile organic compounds (VOC), such as monoterpenes, through a process called autoxidation. This process, in which peroxy-radical intermediates isomerize to allow addition of molecular oxygen, is expected to be highly temperature-dependent. Here, we studied the dynamics of HOM formation during alpha-pinene ozonolysis experiments performed at three different temperatures, 20 °C, 0 °C and −15 °C, in the Aarhus University Research on Aerosol (AURA) chamber. We found that the HOM formation, under our experimental conditions (50 ppb alpha-pinene, 100 ppb ozone), decreased considerably as temperature decreased, with molar yields dropping by around a factor of 50 when experiments were performed at 0 °C, compared to 20 °C. At −15 °C, the HOM signals were already close to the detection limit of the nitrate-based Chemical Ionization Atmospheric Pressure interface Time Of Flight (CI-APi-TOF) mass spectrometer used for measuring gas-phase HOM. Surprisingly, very little difference was seen in the mass spectral distribution of the HOM molecules of interest at 0 °C and 20 °C, with e.g. the ratios between the typical HOM products C10H14O7, C10H14O9, and C10H14O11 remaining fairly constant. The more oxidized species have undergone more isomerization steps, yet, at lower temperature, they did not decrease more than the less oxidized species. One possible explanation is be that the rate-limiting step forming these HOM occurs before the products become oxygenated enough to be detected by our CI-APi-TOF (i.e. typically seven or more oxygen atoms). The strong temperature dependence of HOM formation was observed under temperatures highly relevant for the boreal forest, but the exact magnitude of this effect in the atmosphere will be much more complex: the fate of peroxy-radicals is a competition between autoxidation (influenced by temperature and VOC type) and bimolecular termination pathways (influenced mainly by concentration of reaction partners). While the temperature influence is likely smaller in the boreal atmosphere than in our chamber, the magnitude and complexity of this effect clearly deserves more consideration in future studies in order to estimate the ultimate role of HOM on SOA and NPF under different atmospheric conditions.

Lauriane L. J. Quéléver et al.
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Status: final response (author comments only)
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Lauriane L. J. Quéléver et al.
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Short summary
Highly-oxygenated Organic Molecules (HOM) form rapidly in oxidation of monoterpenes and these have been shown to be crucial for organic aerosol formation. We studied the formation of HOM under different temperatures, finding a strong dependence on their yields. As temperatures decrease, the isomerization reactions that allow rapid oxidation by molecular oxygen slow down, and competing reaction pathways can suppress the HOM formation almost completely, especially at highVOC loadings.
Highly-oxygenated Organic Molecules (HOM) form rapidly in oxidation of monoterpenes and these...