Development of new sensor technologies for ambient Mercury and comparison with conventional methods/systems

Abstract

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.