HR: 1330h
AN: A22A-1040    [PDF]
TI: Ice Nucleation of Re-Dispersed African Desert Dust Samples
AU: M\"ohler, O
EM: ottmar.moehler@imk.fzk.de
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: * Schnaiter, M
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: Wagner, R
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: Linke, C
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: Saathoff, H
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: Schurath, U
AF: Forschungszentrum Karlsruhe, IMK-AAF, P.O. Box 3640, Karlsruhe, 76021 Germany
AU: Mangold, A
AF: Forschungszentrum J\"ulich, ICG-1, P.O. Box, J\"ulich, 52425 Germany
AU: Kramer, M
AF: Forschungszentrum J\"ulich, ICG-1, P.O. Box, J\"ulich, 52425 Germany
AB: Number concentration and size of ice crystals in upper tropospheric cirrus clouds is result of a competition between homogeneous and heterogeneous freezing processes and the dynamic partitioning of water between the interstitial vapour phase and the ice surface. High updraft velocities as e.g. occurring in convective cloud systems favour the formation of high ice particle concentrations by homogeneous freezing of solution aerosols which requires ice supersaturations of up to 60%. At lower updrafts, however, heterogeneous ice nuclei, e.g aircraft emitted soot particles or particles originating from the lower boundary layer, may selectively be activated at lower supersaturation. The pristine ice crystals grow by water uptake, thus eventually limiting the maximum supersaturation to values below the homogeneous freezing threshold. Recent measurements during Crystal-Face have shown mineral dust particles originating from northern Africa to act as efficient ice nuclei in the middle troposphere. Using the large coolable and evacuable aerosol chamber AIDA (Aerosol Interaction and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe, we have investigated the freezing thresholds of redispersed African desert dust samples at different cooling rates and temperatures between -40\deg{}C and -70\deg{}C. The mineral dust particles with diameters between about 0.5 and 2 $\mu$m turned out to act as quite effective deposition nuclei at relatively low ice supersaturations. Experimental methods and ice nucleation results will be discussed on the poster. Results from previous AIDA experiments with soot and mineral dust particles coated with sulphuric acid and ammonium sulphate will also be shown.
UR: http://imk-aida.fzk.de
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting