AbstractThermo-mineral springs are widely spread over the volcanic areas of Salerno, a city in southern Italy. Although the water of thermal structures provides beneficial effects on human health, the air is characterized by the presence of potentially toxic compounds, such as hydrogen sulphide (H₂S) and sulphur dioxide (SO₂). Exposure to sulphurous compounds may have detrimental effects on human health, with asthma being the most common. In this study, air concentrations of H₂S and SO₂ in the thermal springs of Contursi Terme (Salerno, Italy) were monitored for 4 months (using both active and passive sampling), along with the chemical and microclimatic characterization of thermal water, to assess workers’ exposure to these pollutants. An in-depth characterization of indoor air at the springs is paramount to establish emission control limits for occupational exposure and to take protective measures. The air concentration of SO₂ varied from 0.11 ± 0.02 to 0.91 ± 0.02 mg/m³, following a seasonal pattern (higher values in winter and lower in spring). Conversely, indoor H₂S concentrations did not vary significantly with time, but outdoor levels (from 0.40 ± 0.03 to 1.90 ± 0.03 mg/m³) were always higher than indoor ones (from 0.11 ± 0.03 to 0.56 ± 0.03 mg/m³). Not negligible air concentrations of these pollutants were detected in this thermal spring workplace, so further investigations are needed to ensure workers’ safety.