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Mineral dust aerosol plays an important role in climate and biogeochemical processes by providing nutrients to marine and terrestrial ecosystems and by influencing the radiation balance of the atmosphere. In turn, mineral dust responds to natural and anthropogenic alterations of land cover and land use resulting from several environmental changes that occurred on different timescales. Contamination by aerosols is a very tangible threat to the cryosphere in the European Alps due to its proximity to highly urbanized areas, cultivated landscapes, and the largest hot desert in the world. We recently developed and assembled a continuous flow analysis system for studying the solid content of ice cores with a high time resolution, focusing on optical characterization methods based on light scattering. The line is designed to provide an integrated measurement of dust particles with Single-Particle Extinction and Scattering (SPES), digital holography, and an optical particle sizer (Abakus). Many of the particles found in ice are efficient scatterers and absorbers close to the size range of the visible light wavelength. We report some preliminary results from ice cores drilled during the ADA270 project, aiming at an in-depth characterization of the samples that provide essential information on the fast climate evolution, which is causing a severe degeneration of glaciers, among other consequences.

The spectral reflectance of snow and ice varies widely depending on several quantities related (1) to the local environmental variables, such as the solar zenith angle and the surface slope, (2) to the physical properties of the snow, such as the grain size and the snow liquid content, and (3) to the presence of light-absorbing particles (LAPs). Different absorption features are displayed in snow spectra. In particular, the absorption at 1030 nm has been exploited for estimating the grain effective radius of snow both from remote and proximal sensing data (Dozier et al., 2009, Garzonio et al., 2018). This absorption feature has been also used for the retrieval of the liquid water content (LWC) of surface snow since it is characterized by a shift toward shorter wavelengths when LWC increases (Green et al., 2006). Taking benefit of this spectral shift of the absorption feature, we applied a continuum removal approach to obtain both the grain equivalent radius and the LWC value. Furthermore, the accumulation of LAPs, such as dust, black carbon, volcanic ash, and pigmented snow algae on the snowpack albedo increases the absorption of solar radiation and induces a positive surface radiative forcing, enhancing the surface melting.In this contribution, we show a retrieval algorithm to estimate the variables of snow (i.e., snow grain size, snow water equivalent, LAPs concentration) by using the openly available radiative transfer model BioSnicar (Bio-optical Snow, Ice, and Aerosol Radiative model) to simulate the spectral albedo of snow and the absorption of solar light in the snowpack. We present data from two experimental sites located in the Eastern Alps (Stelvio Pass and Brenta Dolomites) collected using a Spectral Evolution spectroradiometer. Measured variables of snow with a Snow Sensor device were compared with those estimated from BioSnicar simulations. Moreover, the impurities content in snow samples collected will be analyzed in a laboratory to better constrain modeling results. Remote sensing is a fundamental tool for characterizing snow cover properties, from the accumulation of LAPs to the wet/dry state of the snow, and the use of satellite sensors (e.g. PRISMA) opens the possibility for monitoring their spatial and temporal variability. This may have an important impact on snow hydrology studies, mainly for monitoring snow melting and improving the management of freshwater resources in the Alpine environment.

There is much information to be derived from the airborne dust that can be found in ice cores, especially about the aerosol composition and sources, including the characteristics of the atmosphere of several thousands of years ago. There is, in fact, much still to learn about both the data that can be retrieved and how to interpret them with appropriate models. One of the most striking aspects of these tiny particles is the effect their shape alone has on their scattering and absorption properties, which translate into a contribution to the Earth radiative transfer, especially at the wavelength scale. We show that aggregates of several particles behave differently from compact particles, and non-isometric compact particles can be clearly distinguished from isometric particles as their non-sphericity increases. We report the advances in this direction based on light scattering measurements on the dust content of ice cores drilled from Dome C and Dome B in Antarctica as part of the EPICA project, and provide a physical interpretation in terms of the known models in the field of light scattering by small particles.