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@ARTICLE{Woiwode:185586,
      author       = {Woiwode, W. and Grooß, J.-U. and Oelhaf, H. and Molleker,
                      S. and Borrmann, S. and Ebersoldt, A. and Frey, W. and
                      Gulde, T. and Khaykin, S. and Maucher, G. and Piesch, C. and
                      Orphal, J.},
      title        = {{D}enitrification by large {NAT} particles: the impact of
                      reduced settling velocities and hints on particle
                      characteristics},
      journal      = {Atmospheric chemistry and physics},
      volume       = {14},
      number       = {20},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2014-07012},
      pages        = {11525 - 11544},
      year         = {2014},
      abstract     = {Vertical redistribution of HNO3 through large
                      HNO3-containing particles associated with polar
                      stratospheric clouds (PSCs) plays an important role in the
                      chemistry of the Arctic winter stratosphere. During the
                      RECONCILE (Reconciliation of essential process parameters
                      for an enhanced predictability of Arctic stratospheric ozone
                      loss and its climate interactions) campaign, apparently very
                      large NAT (nitric acid trihydrate) particles were observed
                      by the airborne in situ probe FSSP-100 (Molleker et al.,
                      2014). Our analysis shows that the FSSP-100 observations
                      associated with the flight on 25 January 2010 cannot easily
                      be explained assuming compact spherical NAT particles due to
                      much too short growing time at temperatures below the
                      existence temperature of NAT (TNAT). State-of-the-art
                      simulations using CLaMS (Chemical Lagrangian Model of the
                      Stratosphere; Grooß et al., 2014) suggest considerably
                      smaller particles. We consider the hypothesis that the
                      simulation reproduces the NAT particle masses in a realistic
                      way, but that real NAT particles may have larger apparent
                      sizes compared to compact spherical particles, e.g. due to
                      non-compact morphology or aspheric shape. Our study focuses
                      on the consequence that such particles would have reduced
                      settling velocities compared to compact spheres, altering
                      the vertical redistribution of HNO3. Utilising CLaMS
                      simulations, we investigate the impact of reduced settling
                      velocities of NAT particles on vertical HNO3 redistribution
                      and compare the results with observations of gas-phase HNO3
                      by the airborne Fourier transform spectrometer MIPAS-STR
                      associated with two RECONCILE flights. The MIPAS-STR
                      observations confirm conditions consistent with
                      denitrification by NAT particles for the flight on 25
                      January 2010 and show good agreement with the simulations
                      within the limitations of the comparison. Best agreement is
                      found if settling velocities between 100 and $50\%$ relative
                      to compact spherical particles are considered (slight
                      preference for the $70\%$ scenario). In contrast, relative
                      settling velocities of $30\%$ result in too weak vertical
                      HNO3 redistribution. Sensitivity simulations considering
                      temperature biases of ±1 K and multiplying the simulated
                      nucleation rates by factors of 0.5 and 2.0 affect the
                      comparisons to a similar extent, but result in no effective
                      improvement compared to the reference scenario. Our results
                      show that an accurate knowledge of the settling velocities
                      of NAT particles is important for quantitative simulations
                      of vertical HNO3 redistribution.},
      cin          = {IEK-7},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013},
      pnm          = {234 - Composition and Dynamics of the Upper Troposphere and
                      Stratosphere (POF2-234)},
      pid          = {G:(DE-HGF)POF2-234},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000344165800032},
      doi          = {10.5194/acp-14-11525-2014},
      url          = {https://juser.fz-juelich.de/record/185586},
}