The actively extending axial zone of the southern Apennine mountain belt of Italy is characterized by a substantial flow of non-volcanic gas to the surface. In this study, we have analyzed the correlation between the active tectonic framework of the Matese Ridge area and the high gas emissions found to the southwest, which includes large amounts of CO₂ (up to 99 vol%), CH₄ (up to 0.55 vol%), and He (up to 52 ppmv). We measured CO₂ and CH₄ fluxes of up to 34000 g d⁻¹ and 2000 g d⁻¹, respectively, from zones of focused degassing (gas vents and associated strong diffuse emission). This anomalously high flux of CO₂ (advective plus diffusive) indicates that the study area has one of the largest non-volcanic natural emissions of CO₂ ever measured on Earth. The isotope composition of C in CO₂ and CH₄ shows there is a dominant crustal contribution of emissions (as opposed to a source from the mantle), indicating that thermometamorphism of the buried Apulian Platform carbonates is probably the main cause of CO₂ production. This process has likely been enhanced by Quaternary magmatism, which provides an additional local source of heat triggering decarbonation of Apulian Platform limestones and dolostones at depth. The advective flux is concentrated at gas vents located along active fault segments located at the western tip of a major crustal structure, the South Matese fault zone. We believe that the very high gas emission in the Matese Ridge area is the result of both the presence of a dense network of active fault strands, which provides efficient pathways for fluid flow toward the surface, and the dramatically reduced thickness of the clay-rich mélange zone acting elsewhere in the southern Apennines as a top seal overlying the buried Apulian Platform carbonates.

Radon (²²²Rn) is a natural radioactive gas formed in rocks and soil by the decay of its parent nuclide (238-Uranium). The rate at which radon migrates to the surface, be it along faults or directly emanated from shallow soil, represents the Geogenic Radon Potential (GRP) of an area. Considering that the GRP is often linked to indoor radon risk levels, we have conducted multi-disciplinary research to: (i) define local GRPs and investigate their relationship with associated indoor Rn levels; (ii) evaluate inhaled radiation dosages and the associated risk to the inhabitants; and (iii) define radon priority areas (RPAs) as required by the Directive 2013/59/Euratom. In the framework of the EU-funded LIFE-Respire project, a large amount of data (radionuclide content, soil gas samples, terrestrial gamma, indoor radon) was collected from three municipalities located in different volcanic districts of the Lazio region (central Italy) that are characterised by low to high GRP. Results highlight the positive correlation between the radionuclide content of the outcropping rocks, the soil Rn concentrations and the presence of high indoor Rn values in areas with medium to high GRP. Data confirm that the Cimini–Vicani area has inhalation dosages that are higher than the reference value of 10 mSv/y.

Fiumicino town in the Tiber River delta, near Rome International Airport (Italy), is historically affected by large amounts of carbon dioxide (CO₂) in the ground and gas eruptions triggered by shallow drilling. While it is known that CO₂ originates from carbonate thermometamorphism and/or mantle degassing, the origin of methane (CH₄) associated with CO₂ is uncertain and the outgassing spatial distribution is unknown. Combining isotope gas geochemistry, soil gas, and structural‐stratigraphic analyses, we provide evidence for a hybrid fluid source system, classifiable as Sediment‐Hosted Geothermal System (SHGS), where biotic CH₄ from sedimentary rocks is carried by deep geothermic CO₂ through active segments of a half‐graben. Molecular and isotopic composition of CH₄ and concentration of heavier alkanes (ethane and propane), obtained from gas vents and soil gas throughout the delta area, reveal that thermogenic CH₄ (up to 3.7 vol% in soil gas; δ¹³C_CH4: −37 to −40‰ VPDB‐Vienna Peedee Belemnite, and δ²H_CH4: −162 to −203‰ VSMOW ‐ Vienna Standard Mean Ocean Water in gas vents) prevails over possible microbial and abiotic components. The hydrocarbons likely result from known Meso‐Cenozoic petroleum systems of the Latium Tyrrhenian coast. Overmaturation of source rocks or molecular fractionation induced by gas migration are likely responsible for increased C₁/C₂₊ ratios. CO₂ and CH₄ soil gas anomalies are scattered along NW‐SE and W‐E alignments, which, based on borehole, geomorphologic, and structural‐stratigraphic analyses, coincide with active faults of a half‐graben that seems to have controlled the recent evolution of the Tiber delta. This SHGS can be a source of considerable greenhouse gas emissions to the atmosphere and hazards for humans and buildings.