Efficiency of the deposition mode ice nucleation on mineral dust particles
1Forschungszentrum Karlsruhe, Institute for Meteorology and Climate Research (IMK-AAF), Germany
2Met Office, OBR (Observations Based Research), UK
3University of Manchester, School of Earth, Atmospheric and Environmental Sciences, UK
4Forschungszentrum J&uuuml;lich, Institute of Chemistry and Dynamics of the Geosphere (ICG-I), Germany
5NCAR, MMM (Mesoscale and Microscale Meteorology), USA
*now at: Royal Meteorological Institute, Ozone Research Group, Belgium
Abstract. The deposition mode ice nucleation efficiency of various dust aerosols was investigated at cirrus cloud temperatures between 196 K and 223 K using the aerosol chamber facility AIDA (Aerosol Interaction and Dynamics in the Atmosphere). Arizona test dust (ATD) as a reference material and two dust samples from the Takla Makan desert in Asia (AD1) and Sahara (SD2) were used for the experiments at simulated cloud conditions. The dust particle sizes were almost lognormally distributed with mode diameters between 0.3 µm and 0.5 µm and geometric standard deviations between 1.6 and 1.9. Deposition ice nucleation was most efficient on ATD particles with ice-active particle fractions of about 0.6 and 0.8 at an ice saturation ratio Si<1.15 and temperatures of 223 K and 209 K, respectively. No significant change of the ice nucleation efficiency was found in up to three subsequent cycles of ice activation and evaporation with the same ATD aerosol. The desert dust samples SD2 and AD1 showed a significantly lower fraction of active deposition nuclei, about 0.25 at 223 K and Si<1.35. For all samples the ice activated aerosol fraction could be approximated by an exponential equation as function of Si. This formulation of ice activation spectra may be used to calculate the formation rate of ice crystals in models, if the number concentration of dust particles is known. More experimental work is needed to quantify the variability of the ice activation spectra as function of the temperature and dust particle properties.