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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 11 | Copyright
Atmos. Chem. Phys., 17, 6631-6650, 2017
https://doi.org/10.5194/acp-17-6631-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 06 Jun 2017

Research article | 06 Jun 2017

Investigation of the β-pinene photooxidation by OH in the atmosphere simulation chamber SAPHIR

Martin Kaminski1,a, Hendrik Fuchs1, Ismail-Hakki Acir1,b, Birger Bohn1, Theo Brauers1,†, Hans-Peter Dorn1, Rolf Häseler1, Andreas Hofzumahaus1, Xin Li1,c, Anna Lutz2, Sascha Nehr1,d, Franz Rohrer1, Ralf Tillmann1, Luc Vereecken1, Robert Wegener1, and Andreas Wahner1 Martin Kaminski et al.
  • 1Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 2Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
  • anow at: Bundesamt für Verbraucherschutz, Abteilung 5 – Methodenstandardisierung, Referenzlaboratorien und Antibiotikaresistenz, Berlin, Germany
  • bnow at: Institute of Nutrition and Food Sciences, Food Chemistry, University of Bonn, Bonn, Germany
  • cnow at: State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China
  • dnow at: Verein Deutscher Ingenieure e.V., Kommission Reinhaltung der Luft, Düsseldorf, Germany
  • deceased

Abstract. Besides isoprene, monoterpenes are the non-methane volatile organic compounds (VOCs) with the highest global emission rates. Due to their high reactivity towards OH, monoterpenes can dominate the radical chemistry of the atmosphere in forested areas. In the present study the photochemical degradation mechanism of β-pinene was investigated in the Jülich atmosphere simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber). One focus of this study is on the OH budget in the degradation process. Therefore, the SAPHIR chamber was equipped with instrumentation to measure radicals (OH, HO2, RO2), the total OH reactivity, important OH precursors (O3, HONO, HCHO), the parent VOC β-pinene, its main oxidation products, acetone and nopinone and photolysis frequencies. All experiments were carried out under low-NO conditions ( ≤ 300ppt) and at atmospheric β-pinene concentrations ( ≤ 5ppb) with and without addition of ozone. For the investigation of the OH budget, the OH production and destruction rates were calculated from measured quantities. Within the limits of accuracy of the instruments, the OH budget was balanced in all β-pinene oxidation experiments. However, even though the OH budget was closed, simulation results from the Master Chemical Mechanism (MCM) 3.2 showed that the OH production and destruction rates were underestimated by the model. The measured OH and HO2 concentrations were underestimated by up to a factor of 2, whereas the total OH reactivity was slightly overestimated because the model predicted a nopinone mixing ratio which was 3 times higher than measured. A new, theory-derived, first-generation product distribution by Vereecken and Peeters (2012) was able to reproduce the measured nopinone time series and the total OH reactivity. Nevertheless, the measured OH and HO2 concentrations remained underestimated by the numerical simulations. These observations together with the fact that the measured OH budget was closed suggest the existence of unaccounted sources of HO2. Although the mechanism of additional HO2 formation could not be resolved, our model studies suggest that an activated alkoxy radical intermediate proposed in the model of Vereecken and Peeters (2012) generates HO2 in a new pathway, whose importance has been underestimated so far. The proposed reaction path involves unimolecular rearrangement and decomposition reactions and photolysis of dicarbonyl products, yielding additional HO2 and CO. Further experiments and quantum chemical calculations have to be made to completely unravel the pathway of HO2 formation.

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Monoterpenes emitted by trees are among the volatile organic compounds with the highest global emission rates. The atmospheric degradation of the monoterpene β-pinene was investigated in the atmosphere simulation chamber SAPHIR in Jülich under low NOx and atmospheric β-pinene concentrations. While the budget of OH was balanced, both OH and HO2 concentrations were underestimated in the simulation results. These observations suggest the existence of unaccounted sources of HO2.
Monoterpenes emitted by trees are among the volatile organic compounds with the highest global...
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