[Zurück]

B. G. Pummer, C. Budke, S. Augustin-Bauditz, D. Niedermeier, L. Felgitsch, C. Kampf, R. Huber, K. Liedl, T. Loerting, T. Moschen, M. Schauperl, M. Tollinger, C. Morris, H. Wex, H. Grothe, U. Pöschl, T. Koop, J. Fröhlich-Nowoisky:
"Ice nucleation by water-soluble macromolecules";
Atmospheric Chemistry and Physics, 15 (2015), S. 4077 - 4091.

Cloud glaciation is critically important for the
global radiation budget (albedo) and for initiation of precipitation.
But the freezing of pure water droplets requires
cooling to temperatures as low as 235 K. Freezing at higher
temperatures requires the presence of an ice nucleator, which
serves as a template for arranging water molecules in an
ice-like manner. It is often assumed that these ice nucleators
have to be insoluble particles. We point out that also
free macromolecules which are dissolved in water can efficiently
induce ice nucleation: the size of such ice nucleating
macromolecules (INMs) is in the range of nanometers, corresponding
to the size of the critical ice embryo. As the latter
is temperature-dependent, we see a correlation between the
size of INMs and the ice nucleation temperature as predicted
by classical nucleation theory. Different types of INMs have
been found in a wide range of biological species and comprise
a variety of chemical structures including proteins, saccharides,
and lipids. Our investigation of the fungal species
Acremonium implicatum, Isaria farinosa, and Mortierella
alpina shows that their ice nucleation activity is caused by
proteinaceous water-soluble INMs. We combine these new
results and literature data on INMs from fungi, bacteria, and
pollen with theoretical calculations to develop a chemical interpretation of ice nucleation and water-soluble INMs. This
has atmospheric implications since many of these INMs can
be released by fragmentation of the carrier cell and subsequently
may be distributed independently. Up to now, this
process has not been accounted for in atmospheric models.

ice nucleation, macromolecules, ice clouds

http://dx.doi.org/10.5194/acp-15-4077-2015

www.atmos-chem-phys.net/15/4077/2015/