A spectroscopic view of mineral aerosol surface aging under atmospheric conditions

Atmospheric mineral aerosols have direct and indirect influence on the climate system. So far, atmospheric interactions studies have mainly focused on pristine samples, despite the fact that aerosol particles may age under natural atmospheric conditions. For example, multiple freeze-melt or evaporation-condensation cycles of an aerosol-containing cloud droplet can change the surface chemistry of the aerosol particle, the droplet ionic strength and pH. These changes have a large impact on the ice nucleation ability of the aerosol particles. We probe the water structure and surface chemistry at water-mineral interface using surface spectroscopic techniques, particularly supercooled nonlinear spectroscopy [1-4]. We found that successive freeze-melt cycles disrupt the dissolution equilibrium, substantially changing the surface chemistry, giving rise to variations ice nucleation ability of the surface [4]. Along the aging process, the restructuring of the water molecules at the surface upon cooling changes. This was found to be correlated to the ice nucleation ability of the surface. We present here a spectroscopic overview on aging of selected mineral surfaces (Al₂O₃, Silica, Mica and PbO). We found that the pH, ionic strength, time in contact with water and number of freezing-melting events influence the aging dynamics and hence the ice nucleation ability.

 

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2. Abdelmonem, A., et al., Surface-Charge-Induced Orientation of Interfacial Water Suppresses Heterogeneous Ice Nucleation on α-Alumina (0001). Atmos. Chem. Phys., 2017. 17(12): p. 7827-7837.
3. Lützenkirchen, J., et al., A set-up for simultaneous measurement of second harmonic generation and streaming potential and some test applications. Journal of Colloid and Interface Science, 2018. 529: p. 294-305.
4. Abdelmonem, A., et al., Cloud history changes water-ice-surface interactions of oxide mineral aerosols (e.g. Silica). Atmos. Chem. Phys. Discuss., 2019. 2019: p. 1-17.