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Venturi, S.
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- PublicationOpen AccessA multi-instrumental geochemical approach to assess the environmental impact of CO2-rich gas emissions in a densely populated area: the case of Cava dei Selci (Latium, Italy)(2019)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ;; ; The Colli Albani volcanic complex (Lazio, Italy) hosts areas characterized by anomalously high emissions of CO2-rich gases (e.g. Tivoli, Cava dei Selci, Tor Caldara, Solforata). The source of these gases is a regional aquifer within the Mesozoic carbonate rock sequences. These degassing zones release significant concentrations of H2S and other toxic gases (e.g. GEM: Gaseous Elemental Mercury, and Rn) and represent a serious hazard for local inhabitants, especially for those living at Cava dei Selci (near Rome, Italy), where the emitting areas are nested inside residential neighborhoods. In April 2016, a comprehensive geochemical survey was carried out in an abandoned stone quarry nearby the urban settlement aimed to: (i) investigate the gas composition from both punctual discharges and anomalously high diffuse soil degassing sites, and (ii) evaluate their environmental impact on the local air quality. The spatial distribution of the soil CO2 fluxes was mainly dependent on the local geostructural setting, whereas shallow secondary processes (e.g. oxidation and gas-water interaction) likely represent the main controlling factor on reactive and/or water-soluble gas species, such as CH4 and H2S. The total output of CO2 from the abandoned stone quarry accounted for 0.53% of total CO2 discharged from the whole Colli Albani volcanic district. The naturally emitted toxic gases (e.g. CO2, H2S, CH4, GEM) largely affect the air quality and pose a serious threat for the health of the local residents. A mobile multi-instrumental station able to continuously and simultaneously acquire CO2, H2S, SO2, CH4, GEM and CO was deployed to verify the concentrations of both the main deep-originated gas compounds and potential secondary gaseous contaminants (i.e. SO2) around and inside the urban settlement most exposed to the lethal gases. Hydrogen sulfide was found to be the most impacting gas, occasionally exceeding the 24-h air quality guideline for ambient air and causing odor annoyance at a distance up to more than 250 m downwind from the emitting area. In poorly ventilated basements, toxic gas accumulations up to hazardous levels were measured, producing anomalous outdoor air concentrations at the street level in front of the descending vehicular access to private garages and relatively far from the main emitting area. The geochemical survey, carried out via mobile station and soil gas measurements, resulted to be particularly efficient for evaluating the potential effects caused by gas emissions in inhabited areas. The multi-measurement approach adopted in the present study is of paramount importance for managing future urban development plans.1081 104 - PublicationOpen AccessFractionation processes affecting the stable carbon isotope signature of thermal waters from hydrothermal/volcanic systems: The examples of Campi Flegrei and Vulcano Island (southern Italy)(2017)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The carbon isotopic composition of dissolved C-bearing species is a powerful tool to discriminate the origin of carbon in thermal waters from volcanic and hydrothermal systems. However, the δ13C values of dissolved CO2 and TDIC (Total Dissolved Inorganic Carbon) are often different with respect to the isotopic signature that characterizes the potential carbon primary sources, i.e. deep hydrothermal reservoirs, magmatic gases and organic activity. The most commonly invoked explanation for such isotopic values is related to mixing processes between deep and shallow end-members. Nevertheless, experimental and empirical investigations demonstrated that isotopic fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to reproduce the measured isotopic values. In this paper,we investigated the chemistry of thermalwaters, collected at Campi Flegrei and Vulcano Island (southern Italy),whose origin is related to interaction processesamongmagmatic gases, meteoric water, seawater and hosting rocks. A special focus was dedicated to the δ13C values of dissolved CO2 (δ13CCO2(aq)) and total dissolved inorganic carbon (δ13CTDIC). The δ13CCO2(aq) and δ13CTDIC values in the water samples fromboth these systems ranged from(i) those measured in fumarolic gases, likely directly related to the deep hydrothermal-magmatic reservoir, and (ii) those typically characterizing biogenic CO2, i.e. produced by microbially-driven degradation of organic matter. A simple mixingmodel of the two end-members, apparently explaining these intermediate carbon isotopic values, contrastswith the chemical composition of the dissolved gases. On the contrary, isotopic fractionation due to secondary processes, such as calcite precipitation, affecting hydrothermal fluids during their underground circulation, seems to exhaustively justify both the chemical and isotopic data. If not recognized, these processes, which frequently occur in volcanic and hydrothermal systems, may lead to an erroneous interpretation of the carbon source, causing an underestimation of the contribution of the hydrothermal/magmatic fluids to the dissolved carbon species. These results pose extreme caution in the interpretation of intermediate δ13CCO2(aq) and δ13CTDIC values for the assessment of the carbon budget of hydrothermal- volcanic systems.393 95 - PublicationRestrictedA new approach for the measurement of gaseous elemental mercury (GEM) and H2S in air from anthropogenic and natural sources: Examples from Mt. Amiata (Siena, Central Italy) and Solfatara Crater (Campi Flegrei, Southern Italy)(2017-04)
; ; ; ; ; ; ; ;Cabassi, J.; Università di Firenze, Dip. Scienze della Terra, Italy ;Tassi, F.; Università di Firenze, Dip. Scienze della Terra, Italy ;Venturi, S.; Università di Firenze, Dip. Scienze della Terra, Italy ;Calabrese, S.; Università di Palermo, DiSTeM ;Capecchiacci, F.; Università di Firenze, Dip. Scienze della Terra, Italy ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Vaselli, O.; Università di Firenze, Dip. Scienze della Terra, Italy; ; ; ; ; ; Real-time measurements of GEM and H2S discharged fromnatural and anthropogenic sources are a valuable tool to investigate the dispersion dynamics of these contaminants in air. In this study, a new approach to measure GEM and H2S concentrations in air, carried out by coupling a portable Zeeman atomic absorption spectrometer with high frequency modulation of light polarization (Lumex RA-915M) and a pulsed fluorescence gas analyzer (Thermo Scientific Model 450i), was applied to two distinct areas: (i) in the surroundings of Piancastagnaio (Siena, Central Italy), located in the eastern flanks ofMt. Amiata (a 200,000 years old volcano), where three geothermal plants are operating and whose exhaust gases are dispersed in the atmosphere after passing through the turbines and an abatement system to mitigate the environmental impact on air, and (ii) at Solfatara Crater (Campi Flegrei, Southern Italy), a volcanic apparatus characterized by intense hydrothermal activity. In 2014, seven GEMand H2S surveys were carried out in the two areas along pre-defined pathways performed by car at both the study sites. The lowest and highest recorded GEM and H2S concentrations at Piancastagnaio were up to 194 and 77 ng/m3, respectively, whilst at Solfatara Crater were up to 690 and 3392 μg/m3, respectively. Although the GEM concentrations at Piancastagnaio were lower than the limit value recommended by local regulations for outdoor environment (300 ng/m3), they were almost one order of magnitude higher than the GEM background both in Tuscany (~3.5 ng/m3) and Mt. Amiata (3–5 ng/m3), suggesting that the main source of GEM was likely related to the geothermal plants. At Solfatara Crater, the highest GEM values were recognized in proximity of the main fumarolic gas discharges. As far as the H2S concentrations are concerned, the guideline value of 150 μg/m3, recommended by WHO (2000), was frequently overcome in the study areas. Dot (in the surroundings of Piancastagnaio) and contour (at Solfatara Crater) maps for GEM and H2S concentrations built for each survey highlighted the important effects played by the meteorological parameters, the latter being measured by a Davis® Vantage Vue weather station. In particular, the GEM and H2S plumes were strongly affected by the wind speed and direction thatwere able to modify the dispersion of the two parameters in air in a matter of hours, indicating that the proposed analytical approach is able to produce a more realistic picture of the distribution of these air pollutants than that provided by using passive traps. Finally, the H2S/GEMratio, calculated by normalizing the measured GEM and H2S concentrations to their highest values (nH2S/GEM),was used as a good proxy for the chemical-physical processes that these two gas species can suffer once emitted in the air. In particular, H2S resulted to be more affected by secondary processes than GEM, possibly related to photochemical oxidation reactions.187 11 - PublicationRestrictedHydrogen sulfide measurements in air by passive/diffusive samplers and high-frequency analyzer: A critical comparison(2016-09)
; ; ; ; ; ; ; ; ;Venturi, S.; Università di Firenze, Dip. Scienze della Terra, Italy ;Cabassi, J.; Università di Firenze, Dip. Scienze della Terra, Italy ;Tassi, F.; Università di Firenze, Dip. Scienze della Terra, Italy ;Capecchiacci, F.; Università di Firenze, Dip. Scienze della Terra, Italy ;Vaselli, O.; Università di Firenze, Dip. Scienze della Terra, Italy ;Bellomo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Calabrese, S.; Università di Palermo, DiSTeM, Italy ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; ; In this study, hydrogen sulfide (H2S) measurements in air carried out using (a) passive/diffusive samplers (Radiello® traps) and (b) a high-frequency (60 s) real-time analyzer (Thermo® 450i) were compared in order to evaluate advantages and limitations of the two techniques. Four different sites in urban environments (Florence, Italy) and two volcanic areas characterized by intense degassing of H2S-rich fluids (Campi Flegrei and Vulcano Island, Italy) were selected for such measurements. The concentrations of H2S generally varied over 5 orders of magnitude (from 10 1e103 mg/m3), the H2S values measured with the Radiello® traps (H2SR) being significantly higher than the average values measured by the Thermo® 450i during the trap exposure (H2STa), especially when H2S was <30 mg/m3. To test the reproducibility of the Radiello® traps, 8 passive/diffusive samplers were contemporaneously deployed within an 0.2 m2 area in an H2S-contaminated site at Mt. Amiata (Tuscany, Italy), revealing that the precision of the H2SR values was ±49%. This large uncertainty, whose cause was not recognizable, is to be added to that related to the environmental conditions (wind speed and direction, humidity, temperature), which are known to strongly affect passive measurements. The Thermo® 450i analyzer measurements highlighted the occurrence of short-term temporal variations of the H2S concentrations, with peak values (up to 5732 mg/m3) potentially harmful to the human health. The Radiello® traps were not able to detect such temporal variability due to their large exposure time. The disagreement between the H2SR and H2STa values poses severe concerns for the selection of an appropriate methodological approach aimed to provide an accurate measurement of this highly toxic air pollutant in compliance with the WHO air quality guidelines. Although passive samplers may offer the opportunity to carry out low-cost preliminary surveys, the use of the high-frequency H2S analyzer is preferred when an accurate assessment of air quality is required. In fact, the latter provides precise real-time measurements for a reliable estimation of the effective exposure to hazardous H2S concentrations, giving insights into the mechanisms regulating the dispersion of this air pollutant in relation to the meteorological parameters.526 46 - PublicationOpen AccessImpact on air quality of carbon and sulfur volatile compounds emitted from hydrothermal discharges: The case study of Pisciarelli (Campi Flegrei, South Italy)Volcanoes are currently to be regarded as natural sources of air pollutants. Climatic and environmental forcing of large volcanic eruptions are well known, although gases emitted through passive degassing during periods of quiescence or hydrothermal activity can also be highly dangerous for the environment and public health. Based on compositional and isotopic data, a survey on the spatial distribution in air of the main volatile compounds of carbon (CO2 and CH4) and sulfur (H2S and SO2) emitted from the fumarolic field of Pisciarelli (Campi Flegrei, Pozzuoli, Naples), a hydrothermal area where degassing activity has visibly increased since 2009, was carried out. The main goals of this study were (i) to evaluate the impact on air quality of these natural manifestations and (ii) inquire into the behavior of the selected chemical species once released in air, and their possible use as tracers to distinguish natural and anthropogenic sources. Keeling plot analysis of CO2 and CH4 isotopes revealed that the hydrothermal area acts as a net source of CO2 in air, whilst CH4 originated mainly from anthropogenic sources. Approaching the urban area, anthropogenic sources of CO2 increased and, at distances greater than 800 m from the Pisciarelli field, they prevailed over the hydrothermal signal. While hydrothermal CO2 simply mixed with that in the atmospheric background, H2S was possibly affected by oxidation processes. Therefore, SO2 measured in the air near the hydrothermal emissions had a secondary origin, i.e. generated by oxidation of hydrothermal H2S. Anthropogenic SO2 was recognized only in the furthest measurement site from Pisciarelli. Finally, in the proximity of a geothermal well, whose drilling was in progress during our field campaign, the H2S concentrations have reached values up to 3 orders of magnitude higher than the urban background, claiming the attention of the local authorities.
155 53 - PublicationRestrictedBiodegradation of CO2, CH4 and volatile organic compounds (VOCs) in soil gas from the Vicano-Cimino hydrothermal system (central Italy)We investigated the effect of microbial activity on the chemistry of hydrothermal fluids related to the Vicano–Cimino system, central Italy. The database included the composition and d13C CO2 and d13C CH4 values for soil gas from an area characterized by intense degassing of fluids having a deep origin. The d13C CH4 values along vertical profiles in the soil indicated that CH4 was controlled by microbial oxidation occurring at shallow (<50 cm) depth, where free O2 was available. This was consistent with the vertical gradients of CH4, H2S and O2 concentrations. The d13C CO2 values in soil gas, characterized by a composition similar to that of the hydrothermal fluids, were not significantly influenced by biodegradation. On the contrary, gas strongly affected by air contamination showed a significant d13C CO2 fractionation. Microbial activity caused strong consumption of hydrothermal alkanes, alkenes, cyclics and hydrogenated halocarbons, whereas benzene was recalcitrant. Oxygenated compounds from hydrocarbon degradation consisted of alcohols, with minor aldehydes, ketones and carboxylic acids. A predominance of alcohols at a high rate of degassing flux, corresponding to a short residence time of hydrothermal gas within the soil, indicated incomplete oxidation. N-bearing compounds were likely produced by humic substances in the soil and/or related to contamination by pesticides, whereas a-pinene traced air entering the soil. The study demonstrates that microbial communities in the soil play an important role for mitigating the release to the atmosphere of C-bearing gases, especially CH4, through diffuse soil degassing, a mechanism that in central Italy significantly contributes to the discharge of CO2-rich gas from deep sources
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