Long-range transport effect on the ice nucleation properties of Saharan dust

Mineral dust is the main responsible ice nucleating particle (INP) type for mixed-phase clouds and has an influence over regions far from the dust source. Parameterizations of the dust ice nucleation (IN) ability used in models are normally obtained from experimental characterization of dust collected from the surface at origin (Ullrich et al., 2017). However, IN properties of long-range transported dust may differ from the dust at origin due to different mineralogy and physical or chemical transformations along the transport route. Here we present preliminary results of ice nucleation properties of Saharan dust transported to Spain and Finland in the temperature range relevant for mixed-phase cloud formation.

In this work, the IN ability in immersion mode is evaluated using an Mk-1 droplet-freezing cold stage (Sikora Scientific Instrumentation). The drop-freezing assays are performed by depositing a set of dust-containing droplets (1 μL) onto a hydrophobic glass that rests atop the cold stage, whose temperature can be varied at a specific cooling rate. A high-resolution camera captures images tracking the freezing events, while the temperature is decreased. Dilutions of the original suspensions are prepared to explore the colder temperature range. Heat treatments are applied to the samples to investigate the contribution of the sample’s biological-origin components to its ice nucleation ability. The BET surface area is measured for selected samples.

This work was supported by the Academy of Finland Flagship ACCC (grant no. 337552) and MEDICEN project (grant no. 345125).

Ullrich, R. et al. (2017). A New Ice Nucleation Active Site Parameterization for Desert Dust and Soot J. Atmos. Sci., 74, 699-717.