摘要：The 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.
