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@ARTICLE{Kanaya:20323,
      author       = {Kanaya, Y. and Hofzumahaus, A. and Dorn, H.-P. and Brauers,
                      T. and Fuchs, H. and Holland, F. and Rohrer, F. and Bohn, B.
                      and Tillmann, R. and Wegener, R. and Wahner, A. and Kajii,
                      Y. and Miyamoto, K. and Nishida, S. and Watanabe, K. and
                      Yoshino, A. and Kubistin, D. and Martinez, M. and Rudolf, M.
                      and Harder, H. and Berresheim, H. and Elste, T. and
                      Plass-Dülmer, C. and Stange, G. and Kleffmann, J. and
                      Elshorbany, Y. and Schurath, U.},
      title        = {{C}omparisons of observed and modeled {OH} and {HO}2
                      concentrations during the ambient measurement period of the
                      {HO}x{C}omp field campaign},
      journal      = {Atmospheric chemistry and physics},
      volume       = {12},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {PreJuSER-20323},
      pages        = {2567 - 2585},
      year         = {2012},
      note         = {Helpful comments by two anonymous reviewers are greatly
                      appreciated. This work was supported by the EU FP-6 program
                      EUROCHAMP (grant no. RII3-CT-2004-505968), ACCENT (Priority
                      1.1.6.3. Global Change and Ecosystems, grant no.
                      GOCE-CT-2004-505337), a Grant-in-Aid for Scientific Research
                      (KAKENHI) (B) 22310018 and RR2002 of the Kyosei Project by
                      the Ministry of Education, Science, Sports, and Culture of
                      Japan. We thank F. J. Johnen for assistance with the
                      experiments and K. D. Lu for discussions.},
      abstract     = {A photochemical box model constrained by ancillary
                      observations was used to simulate OH and HO2 concentrations
                      for three days of ambient observations during the HO(x)Comp
                      field campaign held in Julich, Germany in July 2005. Daytime
                      OH levels observed by four instruments were fairly well
                      reproduced to within $33\%$ by a base model run (Regional
                      Atmospheric Chemistry Mechanism with updated isoprene
                      chemistry adapted from Master Chemical Mechanism ver. 3.1)
                      with high R-2 values (0.72-0.97) over a range of isoprene
                      (0.3-2 ppb) and NO (0.1-10 ppb) mixing ratios. Daytime
                      HO2(*) levels, reconstructed from the base model results
                      taking into account the sensitivity toward speciated RO2
                      (organic peroxy) radicals, as recently reported from one of
                      the participating instruments in the HO2 measurement mode,
                      were $93\%$ higher than the observations made by the single
                      instrument. This also indicates an overprediction of the HO2
                      to OH recycling. Together with the good model-measurement
                      agreement for OH, it implies a missing OH source in the
                      model. Modeled OH and HO2(*) could only be matched to the
                      observations by addition of a strong unknown loss process
                      for HO2(*) that recycles OH at a high yield. Adding to the
                      base model, instead, the recently proposed isomerization
                      mechanism of isoprene peroxy radicals (Peeters and Muller,
                      2010) increased OH and HO2(*) by $28\%$ and $13\%$ on
                      average. Although these were still only $4\%$ higher than
                      the OH observations made by one of the instruments, larger
                      overestimations $(42-70\%)$ occurred with respect to the OH
                      observations made by the other three instruments. The
                      overestimation in OH could be diminished only when reactive
                      alkanes (HC8) were solely introduced to the model to explain
                      the missing fraction of observed OH reactivity. Moreover,
                      the overprediction of HO2(*) became even larger than in the
                      base case. These analyses imply that the rates of the
                      isomerization are not readily supported by the ensemble of
                      radical observations. One of the measurement days was
                      characterized by low isoprene concentrations (similar to 0.5
                      ppb) and OH reactivity that was well explained by the
                      observed species, especially before noon. For this selected
                      period, as opposed to the general behavior, the model tended
                      to underestimate HO2(*). We found that this tendency is
                      associated with high NOx concentrations, suggesting that
                      some HO2 production or regeneration processes under high NOx
                      conditions were being overlooked; this might require
                      revision of ozone production regimes.},
      keywords     = {J (WoSType)},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK491},
      shelfmark    = {Meteorology $\&$ Atmospheric Sciences},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000301547500021},
      doi          = {10.5194/acp-12-2567-2012},
      url          = {https://juser.fz-juelich.de/record/20323},
}