Single Particle Mass Spectrometry of Soil and Dust Particles—Linking their Chemical Composition to Ice-Nucleation Activity

Atmospheric dust and soil dust particles are gaining increasing attention in the research field of cloud microphysics. Their ability to act as heterogeneous ice nuclei (IN) has been shown in various laboratory and field studies (e.g. O'Sullivan et al., 2014; Ansmann et al., 2008); however, their atmospheric relevance in aerosol-cloud interactions is still a matter of current research. This is partly due to the lack of understanding of the actual processes driving ice nucleation on dust and soil dust particles. In contrast to dust from arid source regions, soil dust consists largely of mineral particles with a small fraction of organic matter. Recent studies suggest that especially these biological residues define the ice nucleation properties of soil dust (Conen et al., 2011).

The in-situ identification of these particles by chemical characterization is the goal of the current work. Both, field and laboratory data from dusts and soil dusts of diverse global origin will be presented, linking their chemical composition and ice nucleation behavior. Emphasis is put on their identification in the atmosphere using “chemical fingerprints” from single particle mass spectrometry, and their ice-nucleation activity in the deposition and immersion mode.

Most of the presented data stem from in-situ measurements of Saharan dust and collected airborne particles that were subsequently re-dispersed for laboratory measurements. The measurements were performed (and the dust collected) during the CALIMA (Cloud Affecting particLes In Mineral dust from the sAhara) campaign which aimed at quantifying IN concentrations and onset conditions of ice nucleation in the Saharan Air Layer (SAL) close to the source. CALIMA was conducted at the Izaña Atmospheric Observatory, located west of the African shore on Tenerife, Canary Islands at 2400m a.s.l. for four weeks in August 2013 with a follow-up campaign in August 2014. The mass spectrometry results from CALIMA will be contrasted with those from soil dusts collected in Germany, Argentina, Mongolia, and Arizona Test Dust. For the CALIMA periods, the DREAM8 dust model extended with mineral fractions carried by dust was run to simulate meteorological and dust aerosol conditions for ice nucleation.

References:

Ansmann, A., et al.: Influence of Saharan dust on cloud glaciation in southern Morocco during the Saharan Mineral Dust Experiment, J. Geophys. Res.-Atmos., 113, D04210, 2008.

Conen, F., et al.: Biological residues define the ice nucleation properties of soil dust, Atmos. Chem. Phys., 11, 9643-9648, 2011.

O'Sullivan, D., et al.: Ice nucleation by fertile soil dusts: relative importance of mineral and biogenic components, Atmos. Chem. Phys., 14, 1853-1867, 2014.