An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles R. W. Saunders1, O. Möhler2, M. Schnaiter2, S. Benz2, R. Wagner2, H. Saathoff2, P. J. Connolly3, R. Burgess3, B. J. Murray1, M. Gallagher3, R. Wills1, and J. M. C. Plane1 1School of Chemistry, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK 2Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), 76021 Karlsruhe, Germany 3School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
Abstract. Nanoparticles of iron oxide (crystalline and amorphous), silicon oxide and
magnesium oxide were investigated for their propensity to nucleate ice over
the temperature range 180–250 K, using the AIDA chamber in Karlsruhe,
All samples were observed to initiate ice formation via the deposition mode
at threshold ice super-saturations (RHithresh) ranging from 105% to
140% for temperatures below 220 K. Approximately 10% of amorphous
Fe2O3 particles (modal diameter = 30 nm) generated in situ from a
photochemical aerosol reactor, led to ice nucleation at RHithresh = 140%
at an initial chamber temperature of 182 K. Quantitative analysis
using a singular hypothesis treatment provided a fitted function [ns(190 K)=10(3.33×sice)+8.16]
for the variation in ice-active surface site density (ns:m−2) with
ice saturation (sice) for Fe2O3 nanoparticles. This was
implemented in an aerosol-cloud model to determine a predicted deposition
(mass accommodation) coefficient for water vapour on ice of 0.1 at
temperatures appropriate for the upper atmosphere. Classical nucleation
theory was used to determine representative contact angles (θ) for the
different particle compositions. For the in situ generated Fe2O3
particles, a slight inverse temperature dependence was observed with
θ = 10.5° at 182 K, decreasing to 9.0° at 200 K (compared with
10.2° and 11.4° respectively for the SiO2 and MgO particle
samples at the higher temperature).
These observations indicate that such refractory nanoparticles are
relatively efficient materials for the nucleation of ice under the
conditions studied in the chamber which correspond to cirrus cloud formation
in the upper troposphere. The results also show that Fe2O3
particles do not act as ice nuclei under conditions pertinent for
tropospheric mixed phase clouds, which necessarily form above ~233 K.
At the lower temperatures (<150 K) where noctilucent clouds form during
summer months in the high latitude mesosphere, higher contact angles would
be expected, which may reduce the effectiveness of these particles as ice
nuclei in this part of the atmosphere.
Citation: Saunders, R. W., Möhler, O., Schnaiter, M., Benz, S., Wagner, R., Saathoff, H., Connolly, P. J., Burgess, R., Murray, B. J., Gallagher, M., Wills, R., and Plane, J. M. C.: An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles, Atmos. Chem. Phys., 10, 1227-1247, doi:10.5194/acp-10-1227-2010, 2010.