Preprints
https://doi.org/10.5194/acp-2021-379
https://doi.org/10.5194/acp-2021-379

  11 May 2021

11 May 2021

Review status: this preprint is currently under review for the journal ACP.

Particle-phase processing of α-pinene NO3 secondary organic aerosol in the dark

David M. Bell1, Cheng Wu2, Amelie Bertrand1, Emelie Graham2, Janne Schoonbaert1, Stamatios Giannoukos1,a, Urs Baltensperger1, Andre S. H. Prevot1, Ilona Riipinen2, Imad El Haddad1, and Claudia Mohr2 David M. Bell et al.
  • 1Paul Scherrer Institute, Laboratory of Atmospheric Chemistry, 5232 Villigen, Switzerland
  • 2Department of Environmental Science, Stockholm University, Sweden
  • anow at: ETH Zurich, Department of Chemistry and Applied Biosciences, 8093 Zurich, Switzerland

Abstract. The NO3 radical represents a significant night-time oxidant present in or downstream of polluted environments. There are studies that investigated the formation of secondary organic aerosol (SOA) from NO3 radicals focusing on yields, general composition, and hydrolysis of organonitrates. However, there is limited knowledge about how the composition of NO3-derived SOA evolves as a result of particle phase reactions. Here, SOA was formed from the reaction of α-pinene with NO3 radicals generated from N2O5, and the resulting SOA aged in the absence of external stimuli. The initial composition of NO3-derived α-pinene SOA was slightly dependent upon the concentration of N2O5 injected (excess of NO3 or excess of α-pinene), but was largely dominated by dimer dinitrates (C20H32N2O8-13). Oxidation reactions (e.g. C20H32N2O8 C20H32N2O9 C20H32N2O10 etc...) accounted for 60–70 % of the particle phase reactions observed. Fragmentation reactions and dimer degradation pathways made up the remainder of the particle-phase processes occurring. The exact oxidant is not known, though suggestions are offered (e.g. N2O5, organic peroxides, or peroxy-nitrates). Hydrolysis of −ONO2 functional groups was not an important loss term during dark aging under the relative humidity conditions of our experiments (58–62 %), and changes in the bulk organonitrate composition were likely driven by evaporation of highly nitrogenated molecules. Overall, 25–30 % of the particle-phase composition changes as a function of particle-phase reactions during dark aging representing an important atmospheric aging pathway.

David M. Bell et al.

Status: open (until 06 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-379', Anonymous Referee #1, 05 Jun 2021 reply
  • RC2: 'Comment on acp-2021-379', Anonymous Referee #2, 12 Jun 2021 reply

David M. Bell et al.

David M. Bell et al.

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Short summary
A series of studies designed to investigate the evolution of organic aerosol were performed in an atmospheric simulation chamber, using an oxidant found at night (NO3). The chemical composition steadily changed from its initial composition through different chemical reactions taking place inside of the aerosol. These results show the composition of organic aerosol is steadily changing during its lifetime in the atmosphere.
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