On the complexity of anthropogenic and geological sources of carbon dioxide: Onsite differentiation using isotope surveying

Abstract

Anthropogenic emissions of greenhouse gases (GHGs) co-occur with emissions of these gases from volcanic and urban environments. Therefore, it remains a challenge for the scientific community to identify the contamination sources and quantify the specific contributions. Stable isotopes have many applications in different fields under geosciences, including volcanology, environmental surveying, and climatology. Isotopic surveys allow identification of photosynthetic fractionation in tree forests and gas sources in urban zones, and tracking of volcanic degassing. Thus, the stable isotopic composition of the local GHGs allows the evaluation of the environmental impacts and assists in mitigating the emissions. The present study aimed to distinguish the tropospheric sources of CO2 in the different ecosystems based on the stable isotopic composition of CO2. The study relies on field experiments performed in both volcanic and urban zones of the Mediterranean region. Experiments to identify the CO2 origins in the field were designed and conducted in the laboratory. The CO2 in the air in Palermo, the soil CO2 released at Vulcano (Aeolian Islands, Italy), and the CO2 emitted at Cava dei Selci (Rome, Italy) were selected for conducting case studies. Isotope surveying of the CO2-containing air in Palermo revealed that the CO2 content was correlated to human activity. Mobile-based measurements of carbon isotope were conducted to distinguish the different sources of CO2 at the district scale. In particular, the isotopic surveying process distinguished landfill-related CO2 emissions from the fossil fuel burning ones. The underlying geological reservoir was identified as the main source of air CO2 at Cava dei Selci. Finally, partitioning of soil CO2 enabled estimation of the geological CO2 estimation in the Vulcano Porto settled zones. The results of the present study revealed that detailed investigations on stable isotopes assist in tracking the CO2 sources and the fate of gas emissions. The fine-tuned experimental solutions assisted in broadening the research perspectives. In addition, deeper insights into the carbon cycle were obtained.