PM and material decay: analysis of dry depositions on horizontal and vertical surrogate surfaces through a Deposition Box system

Airborne Particulate Matter (PM), can get removed from the atmosphere through wet and dry mechanisms, and physically/chemically interact with materials and induce premature decay. The effect of dry depositions is a complex issue, especially for outdoor materials, because of the difficulties to collect atmospheric deposits repeatable in terms of mass and homogeneously distributed on the entire investigated substrate. In this work, to overcome these problems by eliminating the variability induced by outdoor removal mechanisms (e.g. winds and rainfalls), a new sampling system called ‘Deposition Box’, was used for PM sampling. Four surrogate materials (Cellulose Acetate, Regenerated Cellulose, Cellulose Nitrate and Aluminum) with different surfaces features were exposed in the urban-marine site of Rimini (Italy), in vertical and horizontal orientations. Homogeneous and reproducible PM deposits were obtained and different analytical techniques (IC, AAS, TOC, VP-SEM-EDX, Vis-Spectrophotometry) were employed to characterize their mass, dimension and composition. Results allowed to discriminate the mechanisms responsible of the dry deposition of atmospheric particles on surfaces with different nature and orientation and to determine which chemical species, and in which amount, tend to preferentially deposit on them. This work demonstrated that “Deposition Box” can represent an affordable tool to study dry deposition fluxes on materials and results obtained will be fundamental in order to extend this kind of exposure to actual building and heritage materials, to investigate the PM contribution in their decay.

A comparison between vertical mixing parameterizations in the Levantine Sea

The goal of this thesis was the study of an optimal vertical mixing parameterization scheme in a mesoscale dominated field characterized from a strong vorticity and the presence of a layer of colder, less saline water at about 100 m depth (Atlantic Waters); in these conditions we compared six different experiments, that differ by the turbulent closure schemes, the presence or not of an enhanced diffusion parameterization and the presence or not of a double diffusion mixing parameterization. To evaluate the performance of the experiments and the model we compared the simulations with the ARGO observations of temperature and salinity available in our domain, in our period of interest. The conclusions were the following: • the increase of the resolution gives better results in terms of temperature in all the considered cases, and in terms of salinity. • The comparisons between the Pacanovski-Philander and the TKE turbulent closure schemes don’t show significant differences when the simulations are compared to the observations. • The removing of the enhanced diffusion parameterization in presence of the TKE turbulent closure submodel doesn’t give positive results, and show limitations in the resolving of gravitational instabilities near the surface • The k-ϵ turbulent closure model utilized in all the GLS experiments, is the best performing closure model among the three considered, with positive results in all the salinity comparison with the in situ observation and in most of the temperature comparisons. • The double mixing parameterization utilized in the k-ϵ closure submodel improves the results of the experiments improving both the temperature and salinity in comparison with the ARGO data.