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Preprints
https://doi.org/10.5194/acp-2020-310
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-310
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Apr 2020

14 Apr 2020

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A revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Photooxidation of pinonaldehyde at ambient conditions investigated in the atmospheric simulation chamber SAPHIR

Michael Rolletter1, Marion Blocquet1,a, Martin Kaminski1,b, Birger Bohn1, Hans-Peter Dorn1, Andreas Hofzumahaus1, Frank Holland1, Xin Li1,c, Franz Rohrer1, Ralf Tillmann1, Robert Wegener1, Astrid Kiendler-Scharr1, Andreas Wahner1, and Hendrik Fuchs1 Michael Rolletter et al.
  • 1Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Jülich GmbH, Jülich, Germany
  • anow at: Ministère de l’Education Nationale et de la Jeunesse, 110 rue de Grenelle, 75357 Paris SP 07
  • bnow at: Federal Office of Consumer Protection and Food Safety, Department 5: Method Standardisation, Reference Laboratories, Resistance to Antibiotics, Berlin, Germany
  • cnow at: College of Environmental Sciences and Engineering, Peking University, Beijing, China

Abstract. The photooxidation of pinonaldehyde, one product of the α-pinene degradation, was investigated in the atmospheric simulation chamber SAPHIR under natural sunlight at low NO concentrations (< 0.2 ppbv) with and without an added hydroxyl radical (OH) scavenger. With scavenger, pinonaldehyde was exclusively removed by photolysis, whereas without scavenger, the degradation was dominated by reaction with OH. In both cases, the observed rate of pinonaldehyde consumption was faster than predicted by an explicit chemical model, the Master Chemical Mechanism (MCM version 3.3.1). In the case with OH scavenger, the observed photolytic decay can be reproduced by the model, if an experimentally determined photolysis frequency is used instead of the parameterization in the MCM. A good fit is obtained, when the photolysis frequency is calculated from the measured solar actinic flux spectrum, absorption cross-sections published by Hallquist et al. (1997), and an effective quantum yield of 0.9. The resulting photolysis frequency is 3.5 times faster than the parameterization in the MCM. When pinonaldehyde is mainly removed by reaction with OH, the observed OH and hydroperoxy radical (HO2) concentrations are underestimated in the model by a factor of 2. Using measured HO2 as a model constraint brings modeled and measured OH concentrations into agreement. This suggests that the chemical mechanism includes all relevant OH producing reactions, but is missing a source for HO2. The missing HO2 source strength of (0.8 to 1.5) ppbv h−1 is similar to the rate of the pinonaldehyde consumption of up to 2.5 ppbv h−1. When the model is constrained by HO2 concentrations and the experimentally derived photolysis frequency, the pinonaldehyde decay is well represented. The photolysis of pinonaldehyde yields 0.18 ± 0.20 formaldehyde molecules at NO concentrations of less than 200 pptv, but no significant acetone formation is observed. When pinonaldehyde is also oxidized by OH under low NO conditions (maximum 80 pptv), yields of acetone and formaldehyde increase over the course of the experiment from 0.2 to 0.3 and from 0.15 to 0.45, respectively. Fantechi et al. (2002) proposed a degradation mechanism based on quantum-chemical calculations, which is considerably more complex than the MCM scheme and contains additional reaction pathways and products. Implementing these modifications results in a closure of the model-measurement discrepancy for the products acetone and formaldehyde, when pinonaldehyde is degraded only by photolysis. In contrast, the underprediction of formed acetone and formaldehyde is worsened compared to model results by the MCM, when pinonaldehyde is mainly degraded in the reaction with OH. This shows that the current mechanisms lack acetone and formaldehyde sources for low NO conditions like in these experiments. Implementing the modifications suggested by Fantechi et al. (2002) does not improve the model-measurement agreement of OH and HO2.

Michael Rolletter et al.

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Michael Rolletter et al.

Michael Rolletter et al.

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Short summary
The photooxidation of pinonaldehyde is investigated in a chamber study under natural sunlight and low NO conditions with and without an added hydroxyl radical (OH) scavenger. The experimentally determined pinonaldehyde photolysis frequency is faster by a factor of 3.5 than currently used parameterizations in atmospheric models. Yields of degradation products are measured in the presence and absence of OH. Measurements are compared to current atmospheric models and a theory-based mechanism.
The photooxidation of pinonaldehyde is investigated in a chamber study under natural sunlight...
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