Daniel J Cziczo et al 2009 Environ. Res. Lett. 4 044013 doi:10.1088/1748-9326/4/4/044013
Daniel J Cziczo1,2,7, Karl D Froyd3,4, Stephane J Gallavardin1,5, Ottmar Moehler6, Stefan Benz6, Harald Saathoff6 and Daniel M Murphy3
Show affiliationsThe ice nucleation characteristics of Arizona test dust (ATD) and illite clay, surrogates for atmospheric ice nuclei, have been determined at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located at the Research Center Karlsruhe in Germany. The objective of this research was to determine the effect of sulfuric acid and ammonium sulfate coatings on the ability of these mineral dust surrogates to nucleate ice in an environment where particles realistically compete for water vapor. Coated ATD particles required higher saturations at all temperatures considered, from −20 to −45 °C, than did identical uncoated particles. Freezing of coated particles often required saturations approaching those for the homogeneous freezing of aqueous solutions of the coating material alone. Less pronounced effects were found for illite, although the presence of a coating consistently increased the saturation or decreased the temperature required for ice formation. Analysis of ice residue at the single particle level suggests that the first coated particles to freeze had thinner or incomplete coatings when compared to particles that froze later in the expansion. This observation highlights a need to verify coating properties since an assumption of homogeneity of a group of coated aerosols may be incorrect. The increase in saturation ratio for freezing suggests that gas-phase uptake of sulfates, a large fraction of which are due to anthropogenic emissions, will reduce the ice and mixed-phase cloud formation potential of atmospheric ice nuclei.
92.60.Mt Particles and aerosols
92.60.hf Tropospheric composition and chemistry, constituent transport and chemistry
92.60.Nv Cloud physics; stratus and cumulus clouds
92.60.hv Pressure, density, and temperature
92.60.Jq Water in the atmosphere (humidity, clouds, evaporation, precipitation)
Issue 4 (October-December 2009)
Received 4 September 2009, accepted for publication 12 November 2009
Published 23 November 2009
Daniel J Cziczo et al 2009 Environ. Res. Lett. 4 044013
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