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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Jun 2019

Submitted as: research article | 26 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Multi-generation OH oxidation as a source for highly oxygenated organic molecules from aromatics

Olga Garmash1, Matti P. Rissanen1,2, Iida Pullinen3,a, Sebastian Schmitt3,b, Oskari Kausiala1,c, Ralf Tillmann3, Carl Percival4, Thomas J. Bannan4, Michael Priestley4,5, Åsa M. Hallquist6, Einhard Kleist7, Astrid Kiendler-Scharr3, Mattias Hallquist5, Torsten Berndt8, Gordon McFiggans4, Jürgen Wildt3,7, Thomas Mentel3, and Mikael Ehn1 Olga Garmash et al.
  • 1Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Helsinki, Finland
  • 2Aerosol Physics Laboratory, Physics Unit, Faculty of Engineering and Natural Sciences, Tampere University, Tampere, Finland
  • 3Institut für Energie- und Klimaforschung, IEK-8: Troposphäre, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 4School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
  • 5Atmospheric Science, Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden
  • 6IVL Swedish Environmental Research Institute, Gothenburg, Sweden
  • 7Institut für Bio- und Geowissenschaften, IBG-2: Pflanzenwissenschaften, Forschungszentrum Jülich GmbH, Jülich, Germany
  • 8Leibniz-Institut für Troposphärenforschung (TROPOS), Permoserstraße 15, 04318 Leipzig, Germany
  • apresent address: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland
  • bpresent address: TSI GmbH, Aachen, Germany
  • cpresent address: Kärsa Oy, Helsinki, Finland

Abstract. Recent studies have recognized highly oxygenated organic molecules (HOM) in the atmosphere as important in the formation of secondary organic aerosol (SOA). A large number of studies have focused on HOM formation from oxidation of biogenically emitted monoterpenes. However, HOM formation from anthropogenic vapours has so far received much less attention. Previous studies have identified the importance of aromatic volatile organic compounds (VOC) for SOA formation. In this study, we investigated several aromatic compounds, benzene (C6H6), toluene (C7H8), and naphthalene (C10H8), for their potential to form HOM upon reaction with hydroxyl radicals (OH). We performed flow tube experiments with all three VOC, and focused in detail on benzene HOM formation in the Jülich Plant Atmosphere Chamber (JPAC). In JPAC, we also investigated the response of HOM to NOx and seed aerosol. Using a nitrate-based chemical ionization mass spectrometer (CI-APi-TOF), we observed the formation of HOM in the flow reactor oxidation of benzene from the first OH attack. However, in the oxidation of toluene and naphthalene, which were injected at lower concentrations, multi-generation OH oxidation seemed to impact the HOM composition. We tested this in more detail for the benzene system in the JPAC, which allowed for studying longer residence times. The results showed that the apparent molar benzene HOM yield under our experimental conditions varied from 4.1 to 14.0 %, with a strong dependence on the OH concentration, indicating that the majority of observed HOM formed through multiple OH-oxidation steps. The composition of the identified HOM in the mass spectrum also supported this hypothesis. By injecting only phenol into the chamber, we found that phenol oxidation cannot be solely responsible for the observed HOM in benzene experiments. When NOx was added to the chamber, HOM composition changed and many oxygenated nitrogen-containing products were observed in CI-APi-TOF. Upon seed aerosol injection, the HOM loss rate was higher than predicted by irreversible condensation, suggesting that some undetected oxygenated intermediates also condensed onto seed aerosol, which is in line with the hypothesis of multi-generation HOM. Based on our results that HOM yield and composition in aromatic systems strongly depend on OH and VOC concentration, we conclude that atmospheric models should account for such dependency and the chemical regime when implementing the quantitative results of laboratory studies. We also suggest that the dependence of HOM yield on chamber conditions may explain part of the variability in SOA yields reported in the literature.

Olga Garmash et al.
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Olga Garmash et al.
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Short summary
Highly oxygenated organic molecules (HOM) facilitate aerosol formation in the atmosphere. Using NO3 chemical ionization mass spectrometry, we investigated HOM composition and yield in oxidation of aromatic compounds at different reactant concentrations, in presence of NOx and seed aerosol. Increased OH concentration increased HOM yield suggesting multiple oxidation steps and affected HOM composition with potential to explain in part discrepancies in published secondary organic aerosol yields.
Highly oxygenated organic molecules (HOM) facilitate aerosol formation in the atmosphere. Using...