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Geothermal areas of Greece are located in regions affected by recent volcanism and in continental basins characterised by elevated heat flow. Many of them are found along the coast, and thus, water is often saline due to marine intrusion. In the current study, we present about 300 unpublished and literature data from thermal and cold mineral waters collected along Greece. Samples were analysed for major ions, Li, SiO2 and isotopes in water. Measured temperatures range from 6.5 to 98 °C, pH from 1.96 to 11.98, while Total Dissolved Solutes (TDS) from 0.22 to 51 g/L. Waters were subdivided into four main groups: (1) thermal; (2) cold; (3) acidic (pH 11). On statistical basis, thermal waters were subdivided into subgroups according to both their temperature [warm ( 75 °C)] and TDS [low salinity ( 30 g/L)]. Cold waters were subdivided based on their pCO2 [low ( 0.85 atm)]. δ18O–H2O ranges from − 12.7 to + 2.7‰ versus SMOW, while δ2H–H2O from − 91 to + 12‰ versus SMOW being generally comprised between the Global Meteoric Water Line and the East Mediterranean Meteoric Water Line. Positive δ18O shifts with respect to the former are mostly related to mixing with seawater, while only for a few samples these shifts point to high-temperature water–rock interaction processes. Only a few thermal waters gave reliable geothermometric estimates, suggesting reservoir temperatures between 80 and 260 °C.

Mt. Etna, in the eastern coast of Sicily (Italy), is one of the most active and most intensely monitored volcanoes of the planet. It is widely recognized as a big source of volcanic gases, such as CO2, SO2 and halogens, to the troposphere in the Mediterranean basin, and its gas emissions account for a significant percentage respect to the worldwide average volcanic budget. The SO2 flux from Mt. Etna’s plume has been routinely measured by the INGV since 1987. SO2 flux ranges between 600 to 25000 Mg/d; fluxes greater than 100000 Mg/d were prevalently measured during eruptive events. During eruptive periods, Etna’s emissions can be dispersed over long distances and cover wide areas of the Mediterranean region. Mt. Etna is also considered a huge source of many trace elements to the atmosphere on regional and global scale. On the morning of December 24th 2018, a moderate lateral eruption of the Mt. Etna started. This eruption was related to an intrusion of a magmatic dike on the high eastern flank of the volcano, through a 2 kilometres long fracture in the NNW SSE direction. At the same time, the summit craters produced a continuous strombolian activity generating a very dense ash plume, dispersed by the wind into the S/SE direction. From June 2018 to June 2019, atmospheric precipitations were collected in the area of Siracusa, a city on the east coast of Sicily, about 80 km SSE of Mt. Etna, and in the area of Milazzo, a city on the northern coast of Sicily. Atmospheric precipitations were monthly collected through a network of 12 pluviometers; the collectors were open during the entire exposure time, receiving both wet and dry deposition (bulk collectors). All the collected water samples were analysed for major ion contents and for a large number of trace elements by ICPOES and ICPMS. During the eruptive period (from 24th to 27th December 2018), the prevailing winds blew from the North direction and there were light rainfalls in the monitored sites (between 0.2 mm in Siracusa and Augusta, and 1.6 mm in Palazzolo Acreide). As a consequence, gases and particles of Etna’s plume were carried for long distance from the emission point, and they were deposited as dry and wet deposition also in the area of Siracusa. During the eruption event and in the following days, the plume reached distances of more than 300 km from the emission point (island of Malta). The samples collected in the study area of Siracusa during the period straddling the eruptive event are characterized by high concentrations of some major ions, such as Fluoride (up to 0.88 mg/l), Chloride (up to 124 mg/l) and Sulphate (23.1 mg/l). These ions derive mainly from the emitted volcanic gases (HF, HCl and SO2). The effect of the described eruption is also visible in the high concentrations of some trace elements, such as Aluminium, Thallium and Tellurium. The mean concentrations of the selected trace elements in the samples collected in the area of Siracusa, in the period before the eruptive event, are: 18.2 μg/l for Aluminium, 0.009 μg/l for Thallium, while Tellurium was always under the detection limit (0.004 μg/l); the concentrations of the same elements in the samples collected during the eruptive event reach 152 μg/l for Aluminium, 0.16 Âg/l for Thallium and 0.025 μg/l for Tellurium, therefore showing a strong enrichment. While Thallium and Tellurium are highly volatile elements typically enriched in volcanic emissions, Aluminium is a refractory element that was probably released by the dissolution of the related volcanic ashes. The study area of Milazzo, due to the prevailing winds from the North direction during the period of the eruption, has not been affected by the plume and therefore the signature of the eruption is not visible in the samples collected in that area, as shown by the mean values of the selected trace elements: 24.2 μg/l, 0.026 μg/l and < 0.004 μg/l for Aluminum, Thallium and Tellurium respectively. In conclusion, close to active volcanic areas, volcanic emissions have to be considered among the major contributors to the chemistry of rainwater, especially during eruptive periods.

Also this year, the “Etna International Training School of Geochemistry. Science meets practice” took place at Mt. Etna, now in its fourth edition. The school was hosted in the historical Volcanological Observatory “Pizzi Deneri”, one of the most important sites of the INGV - Osservatorio Etneo for geochemical and geophysical monitoring. Mount Etna, located in eastern Sicily, is the largest active volcano in Europe and one of the most intensely degassing volcanoes of the world [Allard et al., 1991; Gerlach, 1991]. Mt Etna emits about 1.6 % of global H2O fluxes from arc volcanism [Aiuppa et al., 2008] and 10 % of global average volcanic emission of CO2 and SO2 [D’Alessandro et al., 1997; Caltabiano et al., 2004; Aiuppa et al., 2008; Carn et al., 2017]. Furthermore, Gauthier and Le Cloarec, [1998] underscored that Mt. Etna is an important source of volcanic particles, having a mass flux of particle passively released from the volcano during non-eruptive period estimated between 7 to 23 tons/day [Martin et al., 2008; Calabrese et al., 2011]. In general, Etna is considered to be still under evolution and rather ‘friendly’, which, along with the above, makes it a favorable natural laboratory to study volcanic geochemistry. The Observatory Pizzi Deneri was sponsored by Haroun Tazieff, and it was built in 1978 by the CNR - International Institute of Volcanology under the direction of Prof. Letterio Villari. It is located at the base of the North-East crater (2,850 m a.s.l.), near the Valle del Leone and it was built on the rim of the Ellittico caldera. A picturesque building, consisting of two characteristics domes in front of the breath-taking panorama of the summit craters. Even though it is quite spartan as an accommodation facility, the dormitories, kitchen, seminar room and laboratory are well equipped. In other words, the Pizzi Deneri observatory is a unique place close to the top of the most active volcano of Europe. The observatory lies in a strategic location making it one of the most important sites for monitoring, research and dissemination of the scientific culture. After six field multidisciplinary campaigns (2010-2015) organized by a group of researchers of several institutions (INGV of Palermo, Catania, Naples, Bologna; Universities of Palermo, Florence, Mainz, Heidelberg), the idea of sharing and passing on the experience to the new generation of students has materialized, and the “Etna International Training School of Geochemistry. Science meets practice” was born in 2016. The four editions of the school were partially funded by INGV of Palermo and Catania, European Geoscience Union (EGU), Società Geochimica Italiana (SoGeI) and Associazione Naturalistica Geode. The conceptual idea of the school is to share scientific knowledge and experiences in the geochemical community, using local resources with a low-cost organization in order to allow as many students as possible access to the school. The “Etna International Training School of Geochemistry. Science meets practice” is addressed to senior graduate students, postdoctoral researchers, fellows, and newly appointed assistant professors, aiming to bring together the next generation of researchers active in studies concerning the geochemistry and the budget of volcanic gases. Introduce the participants with innovative direct sampling and remote sensing techniques. Furthermore, it gives young scientists an opportunity to experiment and evaluate new protocols and techniques to be used on volcanic fluid emissions covering a broad variety of methods. The teaching approach includes theoretical sessions (lectures), practical demonstrations and field applications, conducted by international recognized geochemists. We thank all the teachers who helped to make the school possible, among these: Tobias Fischer (University of New Mexico Albuquerque), Jens Fiebig (Institut für Geowissenschaften Goethe-Universität Frankfurt am Main), Andri Stefansson (University of Iceland, Institute of Earth Sciences), Mike Burton (University of Manchester), Nicole Bobrowski (Universität Heidelberg Institute of Environmental Physics and Max Planck Institute for Chemistry), Alessandro Aiuppa (Università di Palermo), Franco Tassi (Università di Firenze), Walter D’Alessandro (INGV of Palermo), Fatima Viveiros (University of the Azores). Direct sampling of high-to-low temperature fumaroles, plume measurement techniques (using CO2/SO2 sensors such as Multi-GAS instruments, MAX-DOAS instruments and UV SO2 cameras, alkaline traps and particle filters), measurement of diffuse soil gas fluxes of endogenous gases (CO2, Hg0, CH4 and light hydrocarbons), sampling of mud volcanoes, groundwaters and bubbling gases. Sampling sites include the active summit craters, eruptive fractures and peripheral areas. The students have shown an active participation both to the lessons and the fieldworks. Most of them describe the school as formative and useful experience for their future researches. Their enthusiasm is the real engine of this school.

On December of 1977, almost 100 years since its last eruption, intense volcanic activity took place in Vulcano Island (Sicily). The elevated fluxes and the temperature increase of the fumaroles in La Fossa Crater, as well as the variations in their chemical composition, alarmed the scientific community. During that period, in the city of Palermo, Marcello Carapezza along with his colleagues Mariano Valenza and Mario Nuccio, were studying the fumarolic field of Vulcano. After extended bibliographic research, Valenza discovered the studies of Ludovico Sicardi, which were focused on Vulcano, Stromboli, Vesuvio and Campi Flegrei. Considering the fact that Sicardi’s research was performed 60 years before its discovery, the scientists decided to meet Sicardi and discuss about his innovative work. They arrived late though; Ludovico had passed away a month before. Carapezza contacted Sicardi’s wife, Zoe, and along with Valenza, went to Sanremo to Sicardi’s house. Zoe provided them with information about his life and suspiciously gave them several boxes containing the scientific material of her husband. Ludovico Sicardi was a chemist and a pharmacist, who was passionate about volcanoes. During his several field trips in Vulcano, he observed and described the fumarolic field on systematic basis, measuring the temperatures and recording their variations over time (Sicardi, 1973). He also performed the first chemical analysis of fluids emitted by fumaroles in Vulcano Island and Solfatara. Furthermore, he was the first to hypothesize the coexistence of SO2 and H2S in fumarolic discharges, which by that time was considered impossible. Also, he succeeded in measuring their ratio by developing an in situ method that chemically separated the S-gaseous species. This method was based on the sampling of fumarolic fluids, using a glass flask that contained a NH4OH-AgNO3 solution, with the aim to dissolve the soluble acid gases (CO2, SO2 and HCl) and block H2S as an insoluble Ag2S (Sicardi, 1955). Based on his articles, Sicardi can be considered as a precursor of the modern volcanic monitoring. The scientific material of Sicardi was well preserved in Valenza’s office and returned to light thirty-five years later, on the 20th of April 2018. This precious material was donated to the Museum of Mineralogy of Palermo and it is nowadays subject of study and cataloging by the collaborators of the Associazione Geode. The donation consists of his scientific field-equipment, glassware, copies of the scientific articles, old maps, photos of Vulcano and Solfatara. Among these, several notes and three important unpublished researches about Vulcano, Vesuvio and Campi Flegrei were found.

Dry and wet depositions provide the pathways through which particles and gases emitted into the atmosphere return to the Earth’s surface. Bulk deposition is defined as the sum of dry and wet deposition, which is characterized by water-soluble and insoluble chemical species. Recent studies (e.g. Castillo et al., 2017) showed that most of the atmospheric deposition in Europe occurs in the wet form, but in southern European regions the role of dry contribution can be as significant as that of wet deposition. In the framework of the multidisciplinary project “CISAS” (Centro Internazionale di Studi Avanzati su Ambiente, ecosistema e Salute umana), bulk depositions were monthly sampled over two polluted industrial areas of Sicily (Milazzo and Priolo), through a network of 12 bulk collectors, from June 2018 to July 2019. In that period, 137 samples were collected and subdivided into 4 aliquots for different analytical determinations: (i) unfiltered aliquots for the total alkalinity; (ii) filtered aliquots (0.45 µm filters) for major anions by ionic chromatography (IC); (iii) filtered and acidified (with Ultrapure HNO3) for the analysis of major cations and a large suite of trace elements, respectively by ICP-OES and ICP-MS; (iv) unfiltered and acidified aliquots for the same suite of trace elements, to evaluate the contribution of less-soluble species. The filtration of the rain samples allows the separation of the water-soluble fraction from the particulate fraction (> 0.45 µm), which is retained by the filter. The comparison between filtered and unfiltered aliquots allowed to highlight the different geochemical mobility of the trace elements, and their distribution among the two fractions. The unfiltered aliquots, therefore, represent the less-soluble species found in the particulate under typical rainwater pH values (4 – 8), that becomes soluble due to the acidification of the samples (pH < 1). Results showed that the less-soluble fraction represents a significant part of the bulk deposition for several trace metals, especially during dry-dominated periods which are characterized by a long-range transport of geogenic particles (e.g. desert dust). In particular, Al, B, Ba, Fe, Li, Sr, and Ti showed significant enrichment if the less-soluble fraction is included. Similar enrichments are noteworthy also for As, Cr, Co, Cu, Ni, Pb, Se Tl, Te and V which can be attributed to the local industrial atmospheric pollution, as well as to Mt. Etna that is a permanent source of several volcanogenic elements (Brugnone et al., 2020).