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@ARTICLE{Rolletter:889041,
      author       = {Rolletter, Michael and Blocquet, Marion and Kaminski,
                      Martin and Bohn, Birger and Dorn, Hans-Peter and
                      Hofzumahaus, Andreas and Holland, Frank and Li, Xin and
                      Rohrer, Franz and Tillmann, Ralf and Wegener, Robert and
                      Kiendler-Scharr, Astrid and Wahner, Andreas and Fuchs,
                      Hendrik},
      title        = {{P}hotooxidation of pinonaldehyde at ambient conditions
                      investigated in the atmospheric simulation chamber {SAPHIR}},
      journal      = {Atmospheric chemistry and physics},
      volume       = {20},
      number       = {22},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2020-05411},
      pages        = {13701 - 13719},
      year         = {2020},
      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 a scavenger,
                      pinonaldehyde was exclusively removed by photolysis, whereas
                      without a 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 an 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 (HO$_2$)
                      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 HO$_2$.
                      The missing HO$_2$ 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
                      HO$_2$ 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 HO$_2$.},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {243 - Tropospheric trace substances and their
                      transformation processes (POF3-243)},
      pid          = {G:(DE-HGF)POF3-243},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000589618500002},
      doi          = {10.5194/acp-20-13701-2020},
      url          = {https://juser.fz-juelich.de/record/889041},
}