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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-400
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 May 2018

Research article | 14 May 2018

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

Insights into HOX and ROX chemistry in the boreal forest via measurement of peroxyacetic acid, peroxyacetic nitric anhydride (PAN) and hydrogen peroxide

John N. Crowley1, Nicolas Pouvesle1, Gavin J. Phillips1, Raoul Axinte1, Horst Fischer1, Tuukka Petäjä2, Anke Nölscher1, Jonathan Williams1, Korbinian Hens1, Hartwig Harder1, Monica Martinez-Harder1, Anna Novelli1, Dagmar Kubistin1, Birger Bohn3, and Jos Lelieveld1 John N. Crowley et al.
  • 1Division of Atmospheric Chemistry, Max-Planck-Institute für Chemie, Mainz, Germany
  • 2Institute for Atmospheric and Earth System Research INAR / Physics, University of Helsinki, Finland
  • 3Forschungszentrum Juelich GmbH, 52425 Juelich, Germany

Abstract. Unlike many oxidised atmospheric trace gases, which have numerous production pathways, peroxyacetic acid (PAA) and PAN are formed almost exclusively in gas-phase reactions involving the hydroperoxy radical (HO2), the acetyl peroxy radical (CH3C(O)O2) and NO2 and are not believed to be directly emitted in significant amounts by vegetation. As the self-reaction of HO2 is the main photochemical route to hydrogen peroxide (H2O2), simultaneous observation of PAA, PAN and H2O2 can provide insight into the HO2 budget. We present an analysis of observations taken during a summertime campaign in a boreal forest that, in addition to natural conditions, was temporarily impacted by two biomass burning plumes. The observations were analysed using an expression based on a steady-state assumption using relative PAA-to-PAN mixing ratios to derive HO2 concentrations. The steady-state approach generated HO2 concentrations that were generally in reasonable agreement with measurements but sometimes overestimated those observed by factors of two or more. We also used a chemically simple, constrained box-model to analyse the formation and reaction of radicals that define the observed mixing ratios of PAA, H2O2. After nudging the simulation towards observations by adding extra, photochemical sources of HO2 and CH3C(O)O2, the box model replicated the observations of PAA, H2O2, ROOH and OH throughout the campaign, including the biomass-burning influenced episodes during which significantly higher levels of many oxidized trace gases were observed. The model indicates that organic peroxy radicals were present at night in high concentrations that sometimes exceeded those predicted for daytime. A dominant fraction of CH3O2 radical generation was found to arise via reactions of the CH3C(O)O2 radical. Initially divergent measured and modelled HO2 concentrations and daily concentration profiles are reconciled when these organic peroxy radicals are detected (as HO2) at an efficiency of 35%. The organic peroxy radicals are found to play an important role in the recycling of OH radicals subsequent to their loss via reactions with volatile organic compounds.

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Short summary
Simultaneous observation of PAA, PAN and H2O2 are used to provide insight into processes influencing the HOx chemistry of the boreal forest, including two biomass-burning impacted periods. A significant contribution from photolytic HOx sources was included in a box model analysis to align model predictions with measurements. The model predicts high levels of organic peroxy radicals, also at nightime, which were responsible for a strong, positive bias in the LIF-based HO2 measurements.
Simultaneous observation of PAA, PAN and H2O2 are used to provide insight into processes...
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