Distinguishing human related, biological, and geological carbon dioxide in the air through isotopic surveying

<p>Stable isotopes have several applications in geosciences and specifically in volcanology, fluids vs earthquakes studies, environmental surveying, and atmospheric sciences. Both geological and human-related gas sources emit carbon dioxide promoting its molar fraction increase in the lower levels of the atmosphere. The strong dependence of global warming from the carbon dioxide (CO<sub>2</sub>) concentration in the air promoted the detailed investigation of the sources of CO<sub>2</sub>. Land use inspection and the correlated increase of air CO<sub>2</sub> concentration proved often the potential identification of the gas sources. Both the precise identification of the gas source and the specific contribution are still open challenges in environmental surveying. Isotopic signature allows both source identification and tracking fate of carbon dioxide (i.e. natural degassing in volcanic and active tectonic regions, photosynthetic fractionation in tree forests, and human-related emissions in urban zones). The isotopic signature allows evaluating the environmental impact of specific actions and better addressing the mitigation efforts by tracking fate of CO<sub>2</sub>.</p><p>This study aims to identify the CO<sub>2</sub> sources in different ecosystems by using a laser spectrometer that allowed to determine rapidly and with high precision the isotope composition of CO<sub>2</sub> in the space and/or at high frequency (up to 1Hz). Various environments include both volcanic, seismic and urban zones because of their strong effects on the low levels of the atmosphere were considered, showing how this kind of instruments can disclose new horizons, in many different applications and especially in the time domain. In the considered zones, both the anthropogenic and geological sources caused the increases of CO<sub>2</sub> molar fraction in the last few centuries. Suitable case studies were: i) the air CO<sub>2</sub> surveying at Palermo; ii) the soil CO<sub>2</sub> emissions at Vulcano (Aeolian Islands - Italy), and iii) the punctual vent CO<sub>2</sub> emissions at Umbertide (Perugia - Italy).</p><p>The results of this study show detailed investigation of both sources and fate of the CO<sub>2</sub> in various environments. The results of the isotope surveying in Palermo show that air CO<sub>2</sub> correlated with human activities (i.e. house heating, urban mobility, and landfill gas emissions). Comparison with air CO<sub>2</sub> at Umbertide shows the greater contribution of the geogenic reservoir near the active fault of Alto Tiberina Valley. Volcanic CO<sub>2</sub> distinguished from biological CO<sub>2</sub> by different isotopic signature in the soil gases of Vulcano. The soil CO<sub>2</sub> partitioning at the settled zone of Vulcano Porto occurred through both gas source identification and data interpretation through a specifically designed isotopic mixing model.</p><p>This study provides several innovative experimental solutions that are suitable to understand the complexity of carbon cycle and unexplored so far environmental scenarios.</p>