In this study, we investigate how the ice nucleation behavior of desert aerosol is influenced by mineralogy, the presence of crystal water and heat labile organic compounds. We collected our samples from the surface of various deserts worldwide as well as directly from the air after atmospheric transport. With the Portable Ice Nucleation Chamber, PINC, we measured the ice active surface site density (ns) in the deposition and condensation mode. Five samples were measured before and after heating them to 300 °C. In addition we used thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Raman- and infrared- spectroscopy to search for the cause of observed differences in ns. TGA, XRD and infrared spectroscopy were carried out on the bulk material and Raman spectroscopy was carried out on single particles by means of micro-Raman mapping of impacted dust.
Indications for heat labile organic compounds were found in two samples as well as indications for soot. While the ns of one sample increased after heating, in a second sample the release of heat labile organic compounds led to suppression of the ice nucleation ability. In addition, the inorganic composition in the form of crystal water – and the subsequent change in mineralogical composition due to the loss of the crystal water – appears to play a role for one sample. Our study shows that in addition to mineralogy, other factors such as organics and crystal water can alter the ice nucleation behavior of desert aerosol during atmospheric transport in various ways.