Chemical and isotopic characterization of rainwater in volcanic, urban and industrial areas of Sicily (Italy)

Abstract

The chemical composition of rainwater depends on (i) the dissolution of gases and particulate matter emitted by different sources, (ii) the chemical and physical reactions occurring during local and regional scale transport, and (iii) removal processes. The source of major and trace elements dissolved in rainwater can be both natural (e.g. sea salts, volcanic emissions, geogenic dust, biogenic material) and anthropogenic (e.g. industrial plants, vehicular traffic, domestic heating, vessel traffic). A group of trace elements has been recently brought to attention, especially for their possible environmental impacts, the Technology-critical elements (TCEs): Ga, Ge, In, Te, Nb, Ta, Tl, the Platinum Group Elements and most of the rare-earth elements (REE). The current knowledge about the geochemical cycle of TCEs is still scarce and there are not many studies about the concentrations of them in the rainwater. Nevertheless, recent studies (e.g. Brugnone et al., 2020) evidenced a contribution from the volcanic activity for some of them (Te, Tl, and REE). The main aim of this research is to produce an unedited geochemical database on major and trace element concentrations and bulk depositions, in different areas of Sicily: a volcanic area (Mt Etna), two urban (Palermo and Catania), and two industrial areas (Milazzo and Priolo) and a rural monitoring site representative of the regional atmospheric background (Cesarò, Nebrodi Regional Park). The samples will be collected monthly, for almost two years, through a network of 15 bulk collectors, most of which were installed at atmospheric monitoring stations of the “Agenzia Regionale per la Protezione Ambientale - ARPA Sicilia”. Moreover, the isotopic ratios of H and O in the rainwater will be investigated, while an innovative feature of the research will be the determination of the isotopic ratios of isotopes not investigated in previous similar studies: 34S/32S, 11B/10B, 87Sr/86Sr. These isotopes have been studied in matrices such as groundwaters, river and marine waters, in which the above elements show higher concentrations than rainwater. Therefore, a new analytical methodology will be developed to measure these isotopic ratios in rainwater. The isotope fingerprint enables to distinguish the contribution of sea-salt from terrestrial and anthropogenic components, allowing to discriminate the different sources that contribute to the chemical and the isotopic composition of atmospheric bulk deposition in the Mediterranean basin.