Monitoring air pollutants in urbanized hydrothermal areas: challenges and benefits of traditional measurement strategies

Carbon- and sulfur-bearing gases are emitted at relevant amounts from hydrothermal manifestations at Tivoli Terme (Latium, central Italy), where different potential anthropogenic contaminant sources also occur. This study presents a geochemical dataset including CO₂, CH₄, SO_2, and H₂S concentrations and δ¹³C-CO₂ and δ¹³C-CH₄ values measured in air at the center of Tivoli town. The main aim was to evaluate the impact on air quality of hydrothermal manifestations and anthropogenic activities employing a traditional stationary monitoring strategy. The analytical results reveal significant air contamination from both natural and anthropogenic emissions, although gas levels were below outdoor air quality thresholds. Carbon dioxide and CH₄ were primarily linked to anthropogenic sources, while hydrothermal emissions played a secondary role. However, H₂S concentrations up to 282 ppb highlighted a notable impact from hydrothermal emissions surrounding the measurement station, where SO₄-rich pools are located. Nevertheless, the geochemical data did not provide a reliable estimate of the specific contributions from each source. The study identifies key limitations in relying on a single fixed monitoring station, as weather conditions highly influence it and cannot reliably capture the relative impacts of various sources across a broad area. Additionally, compositional and isotopic geochemical parameters often produce ambiguous results, complicating the differentiation of pollution sources. An integrated approach is recommended, combining mobile stations for periodic pollutant mapping with low-cost instruments deployed at strategic locations near potential sources and progressively farther away. This strategy could better track the spatial and temporal evolution of contaminant concentrations, addressing the shortcomings of current monitoring systems and enhancing mitigation efforts.