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

In the lower atmosphere, CO emissions impact human health and ecosystems, making data at this level essential for addressing carbon-cycle and public-health questions. The atmospheric concentration of CO 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 CO profoundly affects the environment, although hydrocarbon combustion is the primary driver of increased atmospheric CO and global warming. Distinguishing geogenic from anthropogenic emissions is challenging, especially through air CO concentration measurements alone. This study presents survey results on the stable isotope composition of carbon and oxygen in CO and airborne CO 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 CO emissions in the atmosphere. To better understand CO emission dynamics and to quantify its volcanic origin a mobile laboratory was used. Results show that CO 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 CO. This study emphasizes the importance of monitoring stable isotopes of atmospheric CO, especially in volcanic areas, contributing valuable insights for environmental and public health management.