Desert dust versus local geological dust in Rome area: mineral composition, size distribution, optical properties and downward radiative flux

Desert dust intrusions at-ground affect, beside mass concentration, the composition of airborne aerosol in the lower troposphere of a site. Relating to particulate components, this reflects in altering the site - specific commonly observed relative abundances of crustal particle types (e.g. silicate minerals, calcite, etc.). Airborne mineral dust influences the energy balance of the Earth - solar system, depending on the chemical and mineralogical nature, shape features and microphysical properties (size distribution and refractive index) of dust particle components. These features mainly act on the direct mechanisms tuning the Earth's radiative budget, that is light scattering and absorption. Therefore, changes occurring in relative abundances of aerosol components at a site may reasonably alter the energy balance of the local atmosphere due to desert dust intrusions at that site. In this work, changes of mineral composition, microphysical and optical properties, and downward radiative flux at BOA (Bottom of Atmosphere), were investigated in the atmosphere of Rome area, relating to the occurrence of at-ground desert dust intrusions compared to the corresponding features specific of the re-suspended geological dust of Rome area. These features were indeed characterized in a recent study (Pietrodangelo et al., under submission); an ad-hoc methodology was developed, which combines individual-particle microanalysis by scanning electron microscope (Philips XL30 ESEM, FEI) combined with X-ray energy-dispersive detector (EDAX/AMETEK), parameterization of the size distribution in R-environment and radiative transfer modelling (RTM) by the 6SV code (Second Simulation of a Satellite Signal in the Solar Spectrum - Vector) (Vermote et al., 2006). Here, the same approach is applied to characterize the desert dust transported at-ground in the Rome area during 20 - 25 May 2014. A rotating Nano MOUDI cascade inpactor was used to collect particles, that were then individually analysed, from each stage. Of major particulate components identified, that is silica and silicate minerals, calcite, gypsum and Fe particles, the aerodynamic diameter, number and volume size distributions were obtained, by SEM XEDS data and bulk density of minerals from literature. Some results on number and volume size distributions of the desert dust and of its silicate and calcite particulate components are showed, respectively, in Figures 1 and 2. The PM10 fraction of the Volcanics term (mainly composed of silicate particles) of Rome lithogenic dust is also reported for comparison. Parameterization of size distributions and RTM of optical properties (single scattering albedo and asymmetry parameter) and of BOA downward radiative flux of desert dust are in progress. Preliminary results evidenced non-negligible differences between airborne desert dust transported at-ground and the local re-suspended Rome lithogenic dust. Differences will be discussed on relative abundances of components, probability density function, optical properties and BOA downward radiative flux between the two dust types.