Unveiling spatial variations in atmospheric CO₂ sources: a case study of metropolitan area of Naples, Italy

In the lower atmosphere, CO₂ emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. The atmospheric concentration of CO₂ is crucial in urban areas due to its connection with air quality, pollution, and climate change, becoming a pivotal parameter for environmental management and public safety. In volcanic zones, geogenic CO₂ profoundly affects the environment, although hydrocarbon combustion is the primary driver of increased atmospheric CO₂ and global warming. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO₂ concentration measurements alone. This study presents survey results on the stable isotope composition of carbon and oxygen in CO₂ and airborne CO₂ concentration in Naples' urban area, including the Campi Flegrei caldera, a widespread hydrothermal/volcanic zone in the metropolitan area. Over the past 50 years, two major volcanic unrests (1969-72 and 1982-84) were monitored using seismic, deformation, and geochemical data. Since 2005, this area has experienced ongoing unrest, involving the pressurization of the underlying hydrothermal system as a causal factor of the current uplift in the Pozzuoli area and the increased CO₂ emissions in the atmosphere. To better understand CO₂ emission dynamics and to quantify its volcanic origin a mobile laboratory was used. Results show that CO₂ levels in Naples' urban area exceed background atmospheric levels, indicating an anthropogenic origin from fossil fuel combustion. Conversely, in Pozzuoli's urban area, the stable isotope composition reveals a volcanic origin of the airborne CO₂. This study emphasizes the importance of monitoring stable isotopes of atmospheric CO₂, especially in volcanic areas, contributing valuable insights for environmental and public health management.