Differentiating anthropogenic and geogenic carbon dioxide (CO2) sources in urban and volcanic environments. Case studies from Sicily (Italy), La Palma and Tenerife (Canary Islands, Spain)

Although our ability to reconstruct precise atmospheric carbon dioxide (CO₂) levels is currently limited to the last 800,000 years, CO₂ has played a fundamental role in regulating Earth's climate and biosphere evolution since the Precambrian.

A significant rise in airborne CO₂ began with the industrial revolution, driven largely by the byproduct release of hydrocarbon combustion. The resulting increase in tropospheric CO₂ concentrations has led to global warming and associated climate change impacts, including rising sea levels, extreme weather events, and biodiversity loss. Urban areas, as major consumers of fossil fuels, are key contributors to rising emissions. However, in geologically active regions, natural volcanic (geogenic) emissions also contribute significantly to the local carbon budget. In such mixed environments, measurements of bulk CO₂ concentration alone cannot resolve the source apportionment between geogenic and anthropogenic origins. Consequently, a combination of concentration measurements and stable isotope analysis is required to distinguish these sources effectively.

This study monitors the stable isotope composition and concentration of CO₂ in Sicily (Italy) and Canary Islands (Spain). Laser-based isotope analyzers were deployed onsite to detect various CO₂ isotopologues. Each instrument measured the various isotopologues of CO₂ (e.g., COO, ¹³COO, and C¹⁸OO), and total CO₂ concentration. Measurements were conducted at Palermo, in the Madonie Mountains, Puerto Naos (La Palma), and Puerto de la Cruz (Tenerife). Data were referenced hourly and calibrated daily using standard reference materials, achieving an accuracy of ± 0.25‰ for isotope compositions and ±1 ppmv for concentration.

We present a comparison of CO₂ isotope compositions across diverse environmental settings. The results demonstrate that volcanic and anthropogenic emissions can be successfully distinguished based on the carbon isotope signature (δ¹³C-CO₂) of atmospheric CO₂. Furthermore, variations in both concentration and isotope composition related to latitude (sub-tropical to mid-latitude) and altitude (sea level to approximately one-hundred meters above sea level) were investigated. These findings highlight the necessity of dual-tracer monitoring (concentration and isotopes) in volcanic and urban regions to evaluate greenhouse gas emission dynamics, inform climate mitigation strategies, and assess environmental health risks.