Nano – and micro- particles optical properties

Among the optical methods developed by the Optical Instrumentation Laboratory over the last two decades, Single Scattering Extinction and Scattering (SPES) has laid the groundwork for advancements in microparticle research [AIP 2015]. A range of portable and tabletop instruments is based on this method, including the flagship line of EOS Srl [link], a spin-off company that recently marked its 10th anniversary. Its key advantage is the time-resolved particle-by-particle approach that enables the acquisition of multiparametric, calibration-free, and model-independent light scattering data.

Leveraging its versatility, SPES has been used to study nanoparticles, colloidal systems, and aggregation dynamics [citcitcit]. In addition to the fundamental properties of discretely inhomogeneous fluids, a common theme connecting these applications is environmental science, specifically, aerosol characterisation. Aerosols are a key component of the climate system, widely distributed across the atmosphere. They influence Earth’s radiative balance by interacting with solar and thermal radiation and facilitating cloud formation.

Large-scale, integrated monitoring using ground-based, satellite-based, and filter-based observations provides valuable insights into its global impact. However, a more refined knowledge of the climatic effects of aerosols also depends on a thorough characterisation of their optical and physical properties at a smaller scale, ideally, at the single-particle level. We designed and deployed SPES instruments for particle analysis in air and meltwater from snow and ice, some of which are currently operating in Antarctica and in Svalbard, as well as our laboratories in Milan. Further activities involve the continuous-flow analysis of ice cores, unique archives to reconstruct the past atmospheric composition, conducted within a collaboration with the EuroCold Laboratory group (European Cold Laboratory Facilities, University of Milan-Bicocca).

Mineral dust is one of the major contributors to atmospheric mass load on a global scale. It consists of micron-sized minerals entrained from arid and poorly vegetated regions by aeolian processes, and spans several orders of magnitude in size, with some particles over 100 micrometers. Wet and dry deposition of dust particles on the cryosphere lowers its albedo, accelerating glacier retreat and hindering perennial snow. Moreover, its temperature-driven mobility allows dust to alter the radiative balance of the snowpack in its deep layers, changing the local thermodynamic conditions that determine their evolution and structural stability.