[Zurück]

T. Zolles, H. Grothe, B. G. Pummer:
"Immersion freezing on mineral dust particles";
Poster: European Geosciences Union - General Assembly 2013, Wien; 07.04.2013 - 12.04.2013; in: "Geophysical Research Abstracts", 15 (2013).

Mineral dust is considered to play a major role in ice cloud nucleation in the troposphere. More than 1.000 Tg of
mineral dust are aerosolized from the ground every year, 1-10% of these reach the upper troposphere [1]. At an
altitude of about 8 km ice residual particle analysis has shown that about 50% of all ice nuclei (IN) are mineral
dust[2]. In principle, natural occurring dusts may either be IN-active themselves or are carriers of organic and/or
biological IN. Up to now the ice nucleation, i.e. cloud glaciation, has not been quantized. However, different
authors report a high IN-activity for many mineral dust samples, although a systematic comparison between
different minerals is still missing. Therefore, we studied selected mineral dust samples which were characterized
by X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy before use.
Oil immersion measurements were performed on the most common minerals, clay materials and volcanic ash. The
median freezing temperatures range from -21
C up to homogenous freezing at 38
C. Even though quite a few dust
samples show a reasonable high IN-activity, their median freezing temperatures are low compared to biological
samples [3, 4]. Furthermore, heat treatment of the dusts was applied in order to decompose and to denaturize
organic and/or biological surfactants. Finally, some dust samples had a high loss of activity and thus were subjects
of further experiments. These mineral dust particles were suspended in water and after an incubation time were
removed. In some cases the washing water had become IN-active, but lost its activity after enzymatic treatment.
The observed high IN-activity can thus be explained by adsorbed biological materials. The results suggest that
some mineral dusts are IN-active, and if it is not intrinsic they may even enhance IN-activity of organic and
biological IN if these are adsorbed on the dust particle surface. A relatively high IN-activity of the pure mineral
dusts was only observed in quartz, clays, and mixed natural dusts (ATD), which are mainly composed of SiO
2
and
clays.
References.
[1] C. S. Zender, R. L. Miller and I. Tegen, Eos Trans. AGU, 2004,85, 509.
[2] K. A. Pratt, P. J. DeMott, J. R. French, Z. Wang, D. L. Westphal, A. J. Heymsfield, C. H. Twohy, A. J. Prenni,
K. A. Prather, Nat. Geosci., 2009, 2, 397-400.
[3] B. Pummer, H. Bauer, J. Bernardi, S. Bleicher and H. Grothe, Atmos. Chem. Phys., 2012, 12, 2541-2550.
[4] V. T. J. Phillips, C. Andronache, B. Christner, C. E. Morris, D. C. Sands, A. Bansemer, A. Lauer, C.
McNaughton and C. Seman, Biogeosciences, 2009, 6, 987-1014.

Ice Nucleation, Mineral Dust

http://publik.tuwien.ac.at/files/PubDat_217518.pdf