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@PHDTHESIS{Mangold:40727,
      author       = {Mangold, Alexandor},
      title        = {{U}ntersuchungen zur {M}ikrophysik von {E}iswolken:
                      {S}imulationsexperimente in der {A}erosolkammer {AIDA}},
      volume       = {4146},
      issn         = {0944-2952},
      school       = {Univ. Wuppertal},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-40727, Juel-4146},
      series       = {Berichte des Forschungszentrums Jülich},
      pages        = {VI, 149 S.},
      year         = {2004},
      note         = {Record converted from VDB: 12.11.2012; Wuppertal, Univ.,
                      Diss., 2004},
      abstract     = {The objective of the doctoral thesis presented here is to
                      contribute to an improved understanding of the formation of
                      ice clouds and their micro-physical characteristics.
                      Homogeneous and heterogeneous freezing experiments were
                      carried out with different aerosol types at temperatures
                      between 238 and 185 K and cooling rates between −0.3 and
                      −3.0Kmin$^{−1}$ in the aerosol chamber AIDA (Aerosol
                      Interactions and Dynamics in the Atmosphere). Dynamic cloud
                      processes were simulated in the AIDA by controlled
                      decreasing of pressure and temperature. Homogeneous ice
                      nucleation was examined by means o f freezing processes of
                      fully dissolved sulphuric acid (SA) and ammonium sulphate
                      (AS) droplets. Heterogeneous ice nucleation was triggered by
                      pure soot particles (SOOT), soot particles coated with
                      sulphuric acid or ammonium sulphate (SOOT+SA, SOOT+AS) and
                      two mineral dust types (Arizona Test Dust, ATD and Sahara
                      dust, SD). The sulphuric acid droplets nucleated ice at
                      relative humidities with respect to ice (RH$_{ice,nuc}$) of
                      139 - 166\% (236 - 196 K). This is in accordance with both
                      previous results of AIDA experiments (Möhler et al., 2003)
                      and literature data (Koop et al., 2000). The AS-aerosols
                      generated ice crystals at relative humidities with respect
                      to ice that were significantly below the homogeneous
                      freezing threshold (115 - 136\%). This may be explained by
                      the presence of (micro-) crystalline ammonium sulphate and
                      therefore heterogeneous effects. The number of ice crystals
                      formed in the homogeneous freezing experiments increased
                      with decreasing temperature or increasing cooling rate,
                      independently of the starting concentration of aerosol
                      particles. This result is in accordance with the
                      parameterisation of Kärcher and Lohmann (2002a) and
                      confirms that an additional insertion of homogeneously
                      freezing aerosols has no important impact on the
                      microphysics of ice clouds. For heterogeneous freezing
                      processes with pure soot and mineral dust particles (238 -
                      190 K), RH$_{ice,nuc}$ is clearly below the homogeneous
                      freezing threshold. Mineral dust freezes at lower values of
                      RHice (100 - 120\%) than pure soot (111 - 134\%). A
                      sulphuric acid or ammonium sulphate coating of the soot
                      particles raises the respective values close to the
                      homogeneous freezing threshold (120 - 160\% at 230 - 185K).
                      For heterogeneous freezing experiments, no clear increase in
                      the number of ice crystals can be observed with decreasing
                      temperature. With increasing cooling rate, the number of ice
                      crystals only increases for SOOT- and SD-particles. For
                      ATD-particles, there is limited evidence that the starting
                      concentration of the aerosol has an influence on the number
                      of ice crystals formed. Therefore, heterogeneously freezing
                      aerosol particles (especially mineral dust particles) may
                      influence the microphysics of ice clouds and thus have the
                      potential to influence the climate. This confirms results of
                      modelling studies (Kärcher and Lohmann, 2003), which
                      consider freezing processes of externally mixed homogeneous
                      and heterogeneous aerosols. RH$_{ice,nuc}$ and the share of
                      ice-forming particles of an aerosol are parameters for its
                      potential impact on the climate. In conclusion, the aerosol
                      types examined here can, according to these two parameters,
                      be put in the following order of increasing freezing
                      efficiency: SA (RH$_{ice}$ $\thickapprox$ 155\%; Nice
                      $\thickapprox$1.4\%), SOOT+SA and SOOT+AS (both 145\%;
                      1.7\%), AS (130\%; 10\%), SOOT (120\%; 16\%), SD (110\%;
                      37\%) and ATD (110\%; 70\%). This means that the freezing
                      efficiency increases across the scale of fully dissolved,
                      homogeneously freezing aerosols to coated to pure,
                      heterogeneously freezing aerosol particles.},
      cin          = {ICG-I},
      cid          = {I:(DE-Juel1)VDB47},
      pnm          = {Chemie und Dynamik der Geo-Biosphäre},
      pid          = {G:(DE-Juel1)FUEK257},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/40727},
}