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@ARTICLE{Woiwode:820664,
      author       = {Woiwode, Wolfgang and Höpfner, Michael and Bi, Lei and
                      Pitts, Michael C. and Poole, Lamont R. and Oelhaf, Hermann
                      and Molleker, Sergej and Borrmann, Stephan and Klingebiel,
                      Marcus and Belyaev, Gennady and Ebersoldt, Andreas and
                      Griessbach, Sabine and Grooß, Jens-Uwe and Gulde, Thomas
                      and Krämer, Martina and Maucher, Guido and Piesch, Christof
                      and Rolf, Christian and Sartorius, Christian and Spang,
                      Reinhold and Orphal, Johannes},
      title        = {{S}pectroscopic evidence of large aspherical β-{NAT}
                      particles involved in denitrification in the {D}ecember 2011
                      {A}rctic stratosphere},
      journal      = {Atmospheric chemistry and physics},
      volume       = {16},
      number       = {14},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2016-05933},
      pages        = {9505 - 9532},
      year         = {2016},
      abstract     = {We analyze polar stratospheric cloud (PSC) signatures in
                      airborne MIPAS-STR (Michelson Interferometer for Passive
                      Atmospheric Sounding – STRatospheric aircraft)
                      observations in the spectral regions from 725 to 990 and
                      1150 to 1350 cm−1 under conditions suitable for the
                      existence of nitric acid trihydrate (NAT) above northern
                      Scandinavia on 11 December 2011. The high-resolution
                      infrared limb emission spectra of MIPAS-STR show a
                      characteristic “shoulder-like” signature in the spectral
                      region around 820 cm−1, which is attributed to the ν2
                      symmetric deformation mode of NO3− in β-NAT. Using
                      radiative transfer calculations involving Mie and T-Matrix
                      methods, the spectral signatures of spherical and aspherical
                      particles are simulated. The simulations are constrained
                      using collocated in situ particle measurements. Simulations
                      assuming highly aspherical spheroids with aspect ratios (AR)
                      of 0.1 or 10.0 and a lognormal particle mode with a mode
                      radius of 4.8 µm reproduce the observed spectra to a high
                      degree. A smaller lognormal mode with a mode radius of
                      2.0 µm, which is also taken into account, plays only a
                      minor role. Within the scenarios analyzed, the best overall
                      agreement is found for elongated spheroids with
                      AR  =  0.1. Simulations of spherical particles and
                      spheroids with AR  =  0.5 and 2.0 return results
                      very similar to each other and do not allow us to reproduce
                      the signature around 820 cm−1. The observed
                      “shoulder-like” signature is explained by the
                      combination of the absorption/emission and scattering
                      characteristics of large highly aspherical β-NAT particles.
                      The size distribution supported by our results corresponds
                      to ∼ 9 ppbv of gas-phase equivalent HNO3 at the flight
                      altitude of ∼ 18.5 km. The results are compared with
                      the size distributions derived from the in situ
                      observations, a corresponding Chemical Lagrangian Model of
                      the Stratosphere (CLaMS) simulation, and excess gas-phase
                      HNO3 observed in a nitrification layer directly below the
                      observed PSC. The presented results suggest that large
                      highly aspherical β-NAT particles involved in
                      denitrification of the polar stratosphere can be identified
                      by means of passive infrared limb emission measurements.},
      cin          = {IEK-7 / JSC},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-7-20101013 / I:(DE-Juel1)JSC-20090406},
      pnm          = {244 - Composition and dynamics of the upper troposphere and
                      middle atmosphere (POF3-244) / 511 - Computational Science
                      and Mathematical Methods (POF3-511)},
      pid          = {G:(DE-HGF)POF3-244 / G:(DE-HGF)POF3-511},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000381213300040},
      doi          = {10.5194/acp-16-9505-2016},
      url          = {https://juser.fz-juelich.de/record/820664},
}