Fig. 3

Transects through selected zones of the study area to inspect lateral variations of airborne CO₂ concentration (blue line), δ¹⁸O–CO₂ (red line), and δ¹³C-CO₂ (blue line). (a) A–A′ transect (Bacoli). (b) B–B′ transect (Solfatara). (c) C–C′ transect (Downtown). (d) D–D′ transect (Portici).