Ice nucleation active sites: Insights from experiments with mineral dusts and bacteria

The ICIS2007 workshop was held in September 2007 at the AIDA chamber in Karlsruhe with the aim to compare most existing instruments to study ice nucleation and to gain data for several aerosol types acting as ice nuclei (IN). This data is used in the present study to get further insights into the nucleation mechanism and the relevant aerosol parameters which influence the nucleation process.

Two aerosol types show very different and distinct behaviour: Mineral dust samples and aerosols derived from pseudomonas syringae bacteria. While mineral dusts show a slow and steady increase in activated fraction when the relative humdity is increased at a certain temperature, bacterial aerosols show and immediate almost step-like activation followed by a very flat plateau. This can be explained by assuming that active sited in the bacterial samples are very well defined because they are located on specific proteins which typically have no variation in size and chemical nature. On the other hand, mineral dusts have an non-uniform surface with many active sited having different sizes and qualities.

These data sets are compared with theoretical calculations assuming different types and distributions of active sites among the aerosol particles which reflect the aforementioned assumptions.