We investigate the abundance of ice nucleating aerosol particles in the atmosphere.

In non-tropical climates most of the precipitation is formed in mixed phase clouds, when water droplets and ice crystals coexist. Only then cloud elements will grow fast enough within the lifetime of a cloud to reach a size that is large enough to precipitate. The phase of cloud water also affects the radiative properties of clouds and thus climate, since clouds that contain ice reflect more sunlight than “warm” clouds that consist solely of liquid water drops. The atmospheric aerosol particles which initiate the freezing of water in clouds are called ice nucleating particles (INPs). These particles are relatively rare: only about one in 10⁵-10⁶ atmospheric aerosol particles is an INP. Although the major criteria that determine an aerosol particle to be a good INP are known (solid surface, certain size, lattice dimensions and binding energy), their atmospheric abundance, origin and composition are still poorly known. 

In the DFG-Project INUIT we developed the instruments FINCH and FRIDGE to measure properties of INPs both in the atmosphere and from characteristic laboratory test aerosols of atmospheric relevance.

Very little is currently known about the effects of air pollution and climate change on INPs and clouds. For assessing man’s effects on climate due to possible recent changes of INPs and cloud properties, the abundance of INP in the pre-industrial atmosphere must be known. We address this question in the EU RP7 research project BACCHUS by establishing a climatology of INP in the pristine atmosphere at remote sites (e.g. Amazon, Svalbard). Ice cores archive the INP that are deposited from the ancient atmosphere. We analyze INPs in the meltwater of ice cores as an independent source of information (in cooperation with Alfred-Wegener-Institute and University of Berne, Switzerland)

Mature thunderstorm cloud with anvil of ice particles on top (copyright: José Antonio Quirantes Calvo).