Preprints
https://doi.org/10.5194/acp-2020-975
https://doi.org/10.5194/acp-2020-975

  20 Oct 2020

20 Oct 2020

Review status: a revised version of this preprint is currently under review for the journal ACP.

Modelling the impact of gas-phase pyruvic acid on acetaldehyde and peroxy radical formation in the boreal forest

Philipp G. Eger1, Jan Schuladen1, Nicolas Sobanski1, Horst Fischer1, Einar Karu1, Jonathan Williams1, Ville Vakkari2,3, Jos Lelieveld1, and John N. Crowley1 Philipp G. Eger et al.
  • 1Atmospheric Chemistry Department, Max-Planck-Institute for Chemistry, 55128 Mainz, Germany
  • 2Atmospheric Composition Unit, Finnish Meteorological Institute, 00101 Helsinki, Finland
  • 3Atmospheric Chemistry Research Group, Chemical Resource Beneficiation, North-West University, Potchefstroom, South Africa

Abstract. Based on the first measurements of gas-phase pyruvic acid (CH3C(O)C(O)OH) in the boreal forest, we derive effective emission rates of pyruvic acid and compare them with monoterpene emission rates over the diel cycle. Using a data-constrained box-model, we determine the impact of pyruvic acid photolysis on the formation of acetaldehyde (CH3CHO) and the peroxy radicals CH3C(O)O2, CH3O2 and HO2 during an autumn (IBAIRN) and summer (HUMPPA) campaign at the same site. The results are dependent on the photodissociation mechanism of pyruvic acid and we examine different scenarios in which the main photolysis products are either acetaldehyde or the CH3C(O)O2 radical, with different overall quantum yields. If CH3CHO is taken to be the main product (as presently recommended by evaluation panels) we find that pyruvic acid photolysis can be a dominant source of this aldehyde in the boreal forest with a contribution of 79 % (IBAIRN) and 94 % (HUMPPA) and may help explain the high acetaldehyde levels observed during HUMPPA. On the other hand, if photolysis leads mainly to the formation of radicals, the emission of pyruvic acid has a profound impact on the rates of formation of peroxy radicals (with a contribution of ~20–50 %) and shifts the onset of radical production to earlier in the morning when actinic flux is dominated by wavelengths that are too long to initiate efficient ozone photolysis but which are absorbed by pyruvic acid.

Philipp G. Eger et al.

 
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Philipp G. Eger et al.

Philipp G. Eger et al.

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Short summary
We determine the impact of pyruvic acid photolysis on the formation of acetaldehyde and peroxy radicals during summer and autumn in the Finnish boreal forest using a data-constrained box-model. Our results are dependent on the chosen scenario in which the main photolysis products are either acetaldehyde or peroxy radicals, with different overall quantum yields. We highlight that pyruvic acid photolysis can be an important contributor to acetaldehyde formation in remote, forested regions.
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