Fig. 4

The correlation between δ¹³C–CO₂ and the inverse of airborne CO₂ concentration (i.e., Keeling plot). Data were normalized against the Global reference values recorded by NOAA (a https://www.climate.gov/climatedashboard accessed on July 2, 2024. (a) Dataset collected over the target area. (b) Urbanized areas of Naples. Green circles distinguish the subset of measurement collected near the airport (zone C in Fig. 1a) from those collected in downtown Naples (zone B in Fig. 1a). (c) Pozzuoli–Solfatara–Agnano area (zone A in Fig. 1a) Yellow circles distinguish the subset of magmatic origin from that of anthropogenic origin in the area (blue circles).