Tesi di Dottorato

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    Modeling of biological permeable reactive barriers
    (2017-07-11) Arias Arias, Fabian Ernesto; Pantano, Pietro; Straface, Salvatore; Molinari., Raffaele
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    Development of new sensor technologies for ambient Mercury and comparison with conventional methods/systems
    (2018-11-22) Castagna, Jessica; Carbone, Vincenzo; Sprovieri, Francesca
    In the last decades, the global ecosystem has been increasingly threatened by problems, like as, climate change and air pollution, due to the increasing of pollutant emissions that are altering the balance of atmospheric gases. Among the pollutants, Mercury (Hg) plays a significant role due to its toxicity and negative consequences about the environmental and human health. Hg is released in the atmosphere through punctual or diffuse sources, which could be of natural and/or anthropogenic origins. In the atmosphere, Hg could be redistributed towards terrestrial or aquatic receptors, through a complex biogeochemical cycle that involves all natural areas such as the atmosphere, hydrosphere, and geosphere. Although the Hg’s knowledge is improving, the current comprehension about several processes that influence the Hg cycle in the environment, such as chemical-physical processes that affect the mobility of Hg in soils and sediments, or the exchange of Hg gaseous to the air-water interface, is incomplete for both a quantitative description and a proper modeling. The Hg cycle is cross-border, therefore, in recent years, the need to control its processes persuaded to join efforts at a global level. The principal result of the international policies is represented by the Minamata International Convention, of which, its main objective proposes is to reduce drastically the Hg emissions. In 2010, the European Project GMOS - Global Mercury Observation System (FP7) has been approved, in order to support the Minamata Convention, as well as, to examine in deep the Hg cycle, improving the data coverage around the globe, especially in areas where datasets were absent or scarce. The GMOS-Project, coordinated by the UOS of Rende of the CNR-IIA, supported the development of a monitoring network for Hg, with 40 ground-based stations that have to monitor in continuous Hg in the atmosphere and in depositions. Moreover, within the GMOS-project, oceanographic campaign and aircraft measurements, exploring respectively the open sea and the troposphere, had been performed. In this context, the following work of PhD research had been developed. The first part of this work concerned with the comprehension of some Hg processes through two different case-studies: the first regarding the monitoring station of GMOS-network set in Bariloche (Argentina), while the second one, was about the oceanographic campaign, performed on board the research vessel "Minerva Uno" of the CNR, into the basin of the Mediterranean Sea. In both the case-studies, the conventional systems for Hg measurements were employed, according to the reference instruments used within the global network. However, these instruments require an excessive cost of maintenance, and present difficulties in using, especially in pristine areas. These are the motivations of the need of development of new technologies and systems for Hg, which should be cheaper, robust, transportable, with no energy supply, and user-friendly. For this reasons, the main objective proposal of the second part of this PhD thesis is the development of new sensors for the Hg monitoring in the air and wet deposition. Regard the Hg in air, I was involved into the development of passives samples, tested first into laboratories, and then, on field during two seasonal campaigns, performed in five monitoring GMOS stations, three in the Northern Hemisphere (Italy, Russia, China), and two in the Southern Hemisphere (Argentina and South Africa). The preliminary results of comparison between the new passive system and the active conventional system, although have shown some problems, seem to be very promising. To develop new sensors for Hg in wet deposition, the Electrochemical Impedance Spectroscopy (EIS) of a functionalized gold three-electrode has been investigated. The analysis of this sensor, performed in laboratories, showed a good response. vii The work of research carried out during the PhD has allowed examining in deep the chemical-physical processes for Hg thanks to the results of the two case studies treated. Furthermore, I was involved into the development of new sensors, which could represent a good start point for the Hg monitoring, in both air and wet deposition. The employment of new sensors will allow measuring Hg over the whole globe, including the pristine areas, and will provide an improvement of Hg cycle’s knowledge.
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    <> modelling study of atmospheric cycle of mercury and its exchange processes at environmental interfaces
    (2015-12-18) De Simone, Francesco; Bertolini, Roberto; Carbone, Vincenzo; Pirrone, Nicola; HedgecocK, Ian M.
    Since ancient times human activities have significantly altered the natural global Mercury (Hg) cycle through emissions to the environment. Hg is a global pollutant since its predominant atmospheric form, elemental Hg, reacts relatively slowly with the more abundant atmospheric oxidants and is therefore transported long distances from its emission source. Once oxidised however Hg is readily deposited, an can then be converted to the toxic monomethylmercury (MeHg) in soils and natural waters. MeHg is able to bioaccumulate and biomagnify, up to levels at which it is harmful to human health. Mercury pollution is therefore a threat to ecosystem health on a global scale, and is now being addressed by an international agreement, the Minamata Convention. Comprehensive knowledge of the details of the atmospheric Hg cycle is still lacking, and in particular there is some uncertainty regarding the atmospherically relevant reduction-oxidation reactions of mercury and its compounds. The exchange of Hg and its compounds between the atmosphere and the oceans also plays an important role in the cycling of mercury in the environment: understanding and quantifying mercury deposition patterns and fluxes is critically important for the assessment of the present, and future, environmental impact of mercury contamination. ECHMERIT is a global on-line chemical transport model, based on the ECHAM5 global circulation model, with a highly customisable chemistry mechanism designed to facilitate the investigation of both aqueous and gas phase atmospheric mercury chemistry. An improved version of the model which includes a new set of emissions routines, both on-line and off-line, has been developed and used for this thesis to investigate and assess a number of the uncertainties related to the Hg atmospheric cycle. Outputs of multi-year model simulations have been used to validate the model and to estimate emissions from oceans. Various redox mechanisms have been included to assess how chemical reactions influence the models ability to reproduce measured Hg concentrations and deposition flux patterns. To characterize the Hg emissions which result from Biomass Burning , three recent biomass burning inventories (FINNv1.0, GFEDv3.1 and GFASv1.0) were included in the model and used to investigate the annual variation of Hg. The differences in the geographical distribution and magnitude of the resulting Hg deposition fluxes, hence the uncertainty associated with this Hg source, were quantified. The roles of the Hg/CO enhancement ratio, the emission plume injection height, the Hg0 (g) oxidation mechanism and lifetime, and the inventory chosen, as well as their uncertainty were considered. The greatest uncertainties in the total deposition of Hg due to fires were found to be associated with the Hg/CO enhancement ratio and the emission inventory employed. Deposition flux distributions proved to be more sensitive to the emission inventory and the oxidation mechanism chosen, than all the other model parameters. Over 75% of Hg emitted from biomass burning is deposited to the world’s oceans, with the highest fluxes predicted in the North Atlantic and the highest total deposition in the North Pacific. The net effect of biomass burning is to liberate Hg from lower latitudes and disperse it towards higher latitudes where it is eventually deposited. Finally, the model was used to evaluate the fate of the Hg released into the atmosphere by human activities. Anthropogenic emissions are estimated to amount to roughly 2000Mg/y (1000-4000 Mg/y). Hg speciation (elemental, oxidised or associated with particulate matter) is subject to many uncertainties: the extremely variable lifetimes among Hg species, as well as the Hg emission heights, in combination with the complex physical and chemical mechanisms that drive its final fall-out lead to considerable uncertainties. To address this specific issue three anthropogenic Hg emission inventories, namely AMAP-UNEP, EDGAR and Streets, were included in the Model. Different model parametrisations were adopted to trace the fate of Hg to its final receptors and to thoroughly test the model performance against the measurements. Primary anthropogenic Hg contributes up to 40% of the present day Hg deposition. The oxidation mechanism has a significant impact on the geographical distribution of the deposition of Hg emitted from human activities globally, : 63% is deposited to the world’s oceans. The results presented in this thesis provide a new and unique picture of the global cycle of mercury, evaluating and assessing the uncertainties related to many aspects with an on-line Global Circulation Model developed specifically to investigate the global atmospheric Hg cycle.