We describe an optical
approach based on Digital Holography for
single-particle characterization of mineral dust and micrometric particles,
focusing on the analysis of airborne particles in meltwater from Antarctic
ice cores. We record the holograms formed by the superposition of
the transilluminating reference beam and the waves scattered by single
particles. Taking a cue from recent approaches in the field and holography
methods, we process the holograms to recover both optical and morphological
properties of single dust grains. As a considerable advantage over
traditional light-scattering-based methods, holograms give the extinction
cross section of each particle and, by numerically reconstructing
the wavefront propagation, an unambiguous image of each particle whereby
we derive its cross-sectional shape and size. Measurements have been
carried out on samples collected from the recent EAIIST (East Antarctic
International Ice Sheet Traverse) project, some of which show evidence
of volcanic events. The vast majority of the detected particles show
significant deviations from the isometric shape, as confirmed by both
image reconstruction and extinction cross section analysis. By our
analysis, we observe that experimental data have an extinction cross
section up to 3 times lower than that of spherical particles with
the same volume. Therefore, these deviations have an appreciable impact
on the aerosol contribution to radiative forcing: retrieving particle
shape may improve the modeling of the radiative properties of mineral
dust and reduce the associated uncertainties.