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Natural gas hazard was assessed at Cava dei Selci, a residential neighbourhood of Marino (Rome) by a joint study of gas emissions and related health problems. Here a densely urbanized zone with 4000 residents surrounds a dangerous natural gas discharge where, along the years, dozens of animals were killed by the gas. Gas originates from Colli Albani volcano and consists mostly of CO 2 with ~ 1 vol% of H 2 S. In recent years, several gas-related accidents occurred in the urbanized zone (gas blowouts and road collapses). Some houses were evacuated because of hazardous indoor air gas concentration. Gas hazard was assessed by soil CO 2 flux and concentration surveys and indoor and outdoor air CO 2 and H 2 S concentration measurements. Open fields and house gardens release a high quantity of CO 2 (32.23 tonnes * day -1 ). Inside most houses, CO 2 air concentration exceeds 0.1 vol%, the acceptable long-term exposure range. In several houses both CO 2 and H 2 S exceed the IDLH level (Immediately Dangerous to Life and Health). An epidemiological cohort study was carried out on the residents of two Cava dei Selci zones with high (zone A) and medium (zone B) gas hazard exposure, using the rest of Marino as reference zone. We found excess mortality and emergency room visits (ERV) related to high exposure to CO 2 and H 2 S; in particular, an increased risk of mortality and ERV for diseases of central nervous system (HR 1.57, 95% CI 0.76-3.25 and HR 5.82, 95% CI 1.27-26.56, respectively) was found among men living in zone A., (© 2022. The Author(s).)

Soil CO 2 flux and 222 Rn activity measurements may positively contribute to the geochemical monitoring of active volcanoes. The influence of several environmental parameters on the gas signals has been substantially demonstrated. Therefore, the implementation of tools capable of removing (or minimising) the contribution of the atmospheric effects from the acquired time series is a challenge in volcano surveillance. Here, we present 4 years-long continuous monitoring (from April 2007 to September 2011) of radon activity and soil CO 2 flux collected on the NE flank of Stromboli volcano. Both gases record higher emissions during fall–winter (up to 2700 Bq * m − 3 for radon and 750 g m − 2 day − 1 for CO 2 ) than during spring–summer seasons. Short-time variations on 222 Rn activity are modulated by changes in soil humidity (rainfall), and changes in soil CO 2 flux that may be ascribed to variations in wind speed and direction. The spectral analyses reveal diurnal and semi-diurnal cycles on both gases, outlining that atmospheric variations are capable to modify the gas release rate from the soil. The long-term soil CO 2 flux shows a slow decreasing trend, not visible in 222 Rn activity, suggesting a possible difference in the source depth of the of the gases, CO 2 being deeper and likely related to degassing at depth of the magma batch involved in the February–April 2007 effusive eruption. To minimise the effect of the environmental parameters on the 222 Rn concentrations and soil CO 2 fluxes, two different statistical treatments were applied: the Multiple Linear Regression (MLR) and the Principal Component Regression (PCR). These approaches allow to quantify the weight of each environmental factor on the two gas species and show a strong influence of some parameters on the gas transfer processes through soils. The residual values of radon and CO 2 flux, i.e. the values obtained after correction for the environmental influence, were then compared with the eruptive episodes that occurred at Stromboli during the analysed time span (2007–2011) but no clear correlations emerge between soil gas release and volcanic activity. This is probably due to i ) the distal location of the monitoring stations with respect to the active craters and to ii ) the fact that during the investigated period no major eruptive phenomena (paroxysmal explosion, flank eruption) occurred. Comparison of MLR and PCR methods in time-series analysis indicates that MLR can be more easily applied to real time data processing in monitoring of open conduit active volcanoes (like Stromboli) where the transition to an eruptive phase may occur in relatively short times. [ABSTRACT FROM AUTHOR]

Abstract: Gas hazard was evaluated in the three most important cold gas emission zones on the flanks of the quiescent Colli Albani volcano. These zones are located above structural highs of the buried carbonate basement which represents the main regional aquifer and the main reservoir for gas rising from depth. All extensional faults affecting the limestone reservoir represent leaking pathways along which gas rises to the surface and locally accumulates in shallow permeable horizons forming pressurized pockets that may produce gas blowout when reached by wells. The gas, mainly composed of CO2 (>90vol.%), contains appreciable quantities of H2S (0.35–6vol.%), and both represent a potentially high local hazard. Both gases are denser than air and accumulate near ground where they may reach hazardous concentrations, and lethal accidents frequently occur to animals watering at local ponds. In order to evaluate the rate of degassing and the related hazard, CO2 and H2S diffuse soil flux surveys have been repeatedly carried out using an accumulation chamber. The viscous gas flux of some important discrete emissions has been evaluated and the CO2 and H2S air concentration measured by portable devices and by Tunable Diode Laser profiles. The minimum potential lethal concentration of the two gases (250ppm for H2S and 8vol.% for CO2) is 320times higher for CO2, whereas the CO2/H2S concentration ratio in the emitted natural gas is significantly lower (15–159). This explains why H2S reaches hazardous, even lethal, concentrations more frequently than CO2. A relevant hazard exists for both gases in the depressed zones (channels, excavations) particularly in the non-windy early hours of the day. [Copyright &y& Elsevier]

Abstract: La Fossa crater on Vulcano Island is quiescent since 1890. Periodically it undergoes “crises” characterized by marked increase of temperature (T), gas output and concentration of magmatic components in the crater fumaroles (T may exceed 600°C). During these crises, which so far did not lead to any eruptive reactivation, the diffuse CO2 soil degassing also increases and in December 2005 an anomalous CO2 flux of 1350tons/day was estimated by 1588 measurements over a surface of 1.66km2 extending from La Fossa crater to the inhabited zone of Vulcano Porto. The crater area and two other anomalously degassing sites (Levante Beach and Palizzi) have been periodically investigated from December 2004 to August 2010 for diffuse CO2 soil flux. They show a marked variation with time of the degassing rate, with synchronous maxima in December 2005. Carbon dioxide soil flux and environmental parameters have been also continuously monitored for over one year by an automatic station at Vulcano Porto. In order to assess the hazard of the endogenous gas emissions, CO2 and H2S air concentrations have been measured by Tunable Diode Laser profiles near the fumaroles of the crater rim and of the Levante Beach area, where also the viscous gas flux has been estimated. In addition, CO2 air concentration has been measured both indoor and outdoor in an inhabited sector of Vulcano Porto. Results show that in some sites usually frequented by tourists there is a dangerous H2S air concentration and CO2 exceeds the hazardous thresholds in some Vulcano houses. These zones should be immediately monitored for gas hazard should a new crisis arise. [Copyright &y& Elsevier]