Quantification of the Volcanic Carbon Dioxide in the Air of Vulcano Porto by Stable Isotope Surveys

Abstract

Injecting volcanic gas into the air leads to an increase in carbon dioxide (CO2) levels compared with background concentrations and may establish gas hazard conditions. This study reports the results of five stable isotope (i.e., δ13C‐CO2 and δ18O‐CO2) surveys of airborne CO2 on Vulcano from August 2020 to November 2021. To measure CO2 in the air, a mobile laboratory was equipped with a laser‐based spectrophotometer that can selectively detect different CO2 isotopologues. Volcanic CO2 has a different isotopic signature than atmospheric CO2 and both δ13C‐CO2 and δ18O‐CO2 can help trace the injections of volcanic gases into the air. An isotopic mass balance model was developed for partitions CO2 between atmospheric background and volcanic CO2. The results of these studies show that volcanic CO2 emissions and atmospheric circulation deeply affected the concentration of CO2 in the air at Vulcano Porto. Studies of δ13C‐CO2 and δ18O‐CO2 provide an estimate of volcanic CO2 in the air. These results help identify spatially some points of interest for mitigating volcanic gas emission‐related hazards on Vulcano.

Monitoring CO2 Hazards of Volcanic Origin: A Case Study at the Island of Vulcano (Italy) during 2021–2022

“…The four stations measure the ϕCO 2 in the inhabited zone of Vulcano Porto. This study includes the recording of ϕCO 2 during a period of remarkable changes in volcanic degassing due to an increase in magmatic degassing at depth [45][46][47][48]. Overall, statistics for the data collected from each station during the September 2021-December 2022 time window (Table 1) show that the ϕCO 2 at Carapezza and Rojas is within the range of emissions from soil respiration [81][82][83], while the average ϕCO 2 at both Porto and Castello is an order of magnitude higher.…”

“…The gas hazard in volcanic regions is an interface problem caused by the interplay among diffuse degassing, plume dispersal into the La Fossa caldera from the crater rim, and atmospheric turbulence conditions [34,46,77,84,85]. The Rojas monitoring station includes sensors to measure several weather variables that affect both ϕCO 2 and the dispersion of CO 2 in the air in the inhabited zone of Vulcano Porto.…”

“…Arguably, this is particularly noticeable in inadequately ventilated zones or areas where the prevalence of drains, vents, and sewage pipes fosters conditions of heightened permeability to subsurface gases. The results of detailed investigations conducted through spatial surveys of stable isotopes of carbon and oxygen in the air CO 2 suggest that variations in volcanic outgassing and daily evolution of the planetary boundary layer affect the volcanic gas dispersal in the Vulcano Porto area [11,46]. Since the outdoor air CO 2 concentration is a suitable background for both indoor and outdoor CO 2 concentration at the local scale, these results show that the greatest gas hazard can be detected late at night and under conditions of increased volcanic degassing.…”

“…The ϕCO 2 significantly affected the CO 2 concentration in outdoor air at a height of 20 cm at both Rojas and Carapezza sites, while the correlation between CO 2 concentration and ϕCO 2 is more than an order of magnitude lower at Faraglione (i.e., Porto and Castello sites). Air turbulence helps to smooth vertical differences in air CO 2 concentrations by disturbing stratification in the ground-level planetary boundary layer (PBL), especially during daytime hours [9,11,46]. When either hot or less dense air is rising or winds are blowing at high speeds (i.e., >~3 m s −1 ), turbulent motions prevent chemical stratification in the lower layers of the atmosphere.…”

“…The complex problem of controlling the gas hazard with appropriate measures may be exacerbated by the lack of an effective monitoring network. Since late September 2021, volcanic outgassing on the island of Vulcano has increased rapidly [45][46][47][48][49][50], prompting civil defense authorities to warn the public and intensify monitoring efforts.…”