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@ARTICLE{Garmash:902268,
      author       = {Garmash, Olga and Rissanen, Matti P. and Pullinen, Iida and
                      Schmitt, Sebastian and Kausiala, Oskari and Tillmann, Ralf
                      and Zhao, Defeng and Percival, Carl and Bannan, Thomas J.
                      and Priestley, Michael and Hallquist, Åsa M. and Kleist,
                      Einhard and Kiendler-Scharr, Astrid and Hallquist, Mattias
                      and Berndt, Torsten and McFiggans, Gordon and Wildt, Jürgen
                      and Mentel, Thomas F. and Ehn, Mikael},
      title        = {{M}ulti-generation {OH} oxidation as a source for highly
                      oxygenated organic molecules from aromatics},
      journal      = {Atmospheric chemistry and physics},
      volume       = {20},
      number       = {1},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2021-04131},
      pages        = {515 - 537},
      year         = {2020},
      abstract     = {Recent studies have recognised highly oxygenated organic
                      molecules (HOMs) 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 (VOCs) for SOA
                      formation. In this study, we investigated several aromatic
                      compounds, benzene (C6H6), toluene (C7H8), and naphthalene
                      (C10H8), for their potential to form HOMs upon reaction with
                      hydroxyl radicals (OH). We performed flow tube experiments
                      with all three VOCs and focused in detail on benzene HOM
                      formation in the Jülich Plant Atmosphere Chamber (JPAC). In
                      JPAC, we also investigated the response of HOMs to NOx and
                      seed aerosol. Using a nitrate-based chemical ionisation mass
                      spectrometer (CI-APi-TOF), we observed the formation of HOMs
                      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 HOMs formed through multiple OH-oxidation steps.
                      The composition of the identified HOMs 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 HOMs 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 that some of the HOMs
                      were formed in multi-generation OH oxidation. Based on our
                      results, we conclude that HOM yield and composition in
                      aromatic systems strongly depend on OH and VOC concentration
                      and more studies are needed to fully understand this effect
                      on the formation of HOMs and, consequently, SOA. 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 and strongly advise monitoring
                      HOMs in future SOA studies.},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {2111 - Air Quality (POF4-211)},
      pid          = {G:(DE-HGF)POF4-2111},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000507330900001},
      doi          = {10.5194/acp-20-515-2020},
      url          = {https://juser.fz-juelich.de/record/902268},
}