Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)

Abstract

In this paper, fluid source(s) and processes controlling the chemical composition of volatile organic compounds (VOCs) in gas discharges from Mt. Etna and Vulcano Island (Sicily, Italy) were investigated. The main composition of the Etnean and Volcano gas emissions is produced by mixing, to various degrees, of magmatic and hydrothermal components. VOCs are dominated by alkanes, alkenes and aromatics, with minor, though significant, concentrations of O‐, S‐ and Cl(F)‐substituted compounds. The main mechanism for the production of alkanes is likely related to pyrolysis of organic‐matter‐bearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alkene and aromatic compounds via catalytic reactions (dehydrogenation and dehydroaromatization, respectively). Nevertheless, an abiogenic origin for the light hydrocarbons cannot be ruled out. Oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions, typical of these volcanic‐hydrothermal fluids, may explain the production of alcohols, esters, aldehydes, as well as O‐ and S‐bearing heterocycles. By comparing the concentrations of hydrochlorofluorocarbons (HCFCs) in the fumarolic discharges with respect to those of background air, it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes. Finally, chlorofluorocarbon (CFC) abundances appear to be consistent with background air, although the strong air contamination that affects the Mt. Etna fumaroles may mask a possible geogenic contribution for these compounds. On the other hand, no CFCs were detected in the Vulcano gases, which are characterized by low air contribution. Nevertheless, a geogenic source for these compounds cannot be excluded on the basis of the present data.

Volatile organic compounds (VOCs) in soil gases from Solfatara crater (Campi Flegrei, southern Italy): Geogenic source(s) vs. biogeochemical processes

“…In the last four decades, several studies have reported the presence of halocarbons in volcanic emissions, in most cases interpreted as related to the contribution from air contamination (Frische et al, 2006, and references therein). However, some authors (Isidorov et al, 1990(Isidorov et al, , 1992Schwandner et al, 2004Schwandner et al, , 2013Tassi et al, 2012a) reported geochemical evidences suggesting a volcanogenic source for halocarbons, especially the hydrogenated species (HCFCs), cannot be excluded. In the Solfatara fumaroles, as well as in the soil gases characterized by low air contamination (group A), CFCs and CH 3 Cl were not detected (Tables A1 and A2).…”

“…This behavior may be explained admitting that these compounds can have a deep origin. Production of furans through Paal-Knorr synthesis seems to be favored at relatively high temperatures and highly acidic conditions (Tassi et al, 2010(Tassi et al, , 2012a, such as those characterizing the fluid reservoir feeding the Solfatara fumaroles. Theoretically, furans may also be produced in the soil through oxidation of organic matter induced by iron(III) and hydrogen peroxide in the presence of chloride (Huber et al, 2010).…”

Gases in Volcanic Lake Environments

“…Heavier hydrocarbons of thermogenic derivation are also typically present as either trace or ultra-trace species in hydrothermal environments associated with magmatic systems such as White Island (e.g., Taran and Giggenbach 2003), and Vulcano Island (Tassi et al 2012), with alkanes Fig. 3 Variability in hydrothermal and magmatic endmember components in a low temperature fumarole from White Island, New Zealand.…”

Characterization of the Etna volcanic emissions through an active biomonitoring technique (moss-bags): Part 1 – Major and trace element composition

“…Exposure to high atmospheric concentrations of potentially harmful elements in volcanic areas is a problem that should not be neglected because many millions of people visit volcanic areas each year (Erfurt-Cooper and Cooper, 2010) and many of them get close to the volcanic vents, where the emissions are highly concentrated. Etna is one of the major destinations of worldwide volcano tourism and the tourist facilities provide access to areas close to the summit craters which are the source of huge quantities of harmful elements and compounds to the atmosphere (Aiuppa et al, 2004;Calabrese et al, 2011;Tassi et al, 2012).…”