Introduction

OPTICE is a multidisciplinary project aimed at determining and studying the optical properties of airborne dust in the snowpack.

On a global scale, mineral dust accounts for the major contribution to the mass load of airborne particles in the atmosphere. It consists of micron-sized minerals mainly deflated from arid and semiarid regions by eolian processes. It can affect glaciers reducing the albedo and increasing melting or can transform the snowpack leading the formation of melting-refreezing crusts and hoar crystals weak layers. To evaluate these processes, snow and ice cores provide a unique archive to reconstruct the Earth’s past atmospheric composition. Moreover, they can be powerful tools to assess the impact of human activities on the environment, also enabling albedo evaluation and avalanches forecasting.

This project is based on the analysis of snow and ice cores in key sites in the Alps at mid-high altitudes (>3000-3200 m) overall the years.
On these cores we carried out the optical characterization at the European EuroCold laboratory (University of Milano-Bicocca).
The work is focused on the use of the Single Particle Extinction and Scattering (SPES): an optical instrument invented by Marco Potenza some years ago. The breakthrough of the method is represented by the capability of measuring optical properties of particles such as shape and internal structure. This recently brought clear assessments about the shape variability of dust trough time, with important impact on the radiative transfer of the atmosphere in the past (Potenza et al, 2016, Nature Scientific Report).

Radiative transfer is one of the key elements determining climate. It is widely recognized to be strongly affected by aerosols (Intergovernmental Panel on Climate Change 2013). Knowing the optical properties of past and present aerosol is very important in climate modelling for describing the climate change.

At the snow-air interface, the dust particles together with partially melted crystals form crusts during the melting and refreezing cycles. These crusts, once incorporated in the snowpack and with high gradient temperature, allow the formation of thin weak layers of faceted crystals, which increase the instability of the snowpack. Therefore detect the size and shape of dust is important also to have better avalanches evaluations.

Finally a better estimate of dust in the snowpack is essential for melting predictions and a better snow management. This can be useful not only in the ski resorts to correctly estimate artificial snow, but also for water companies to have a forecast on water deriving from the melting of snow and ice.