Real-time monitoring of H2S emissions from the Pisciarelli fumarole at Phlegraean Fields with a Quartz-Enhanced Photoacoustic sensor

The persistent unrest at Campi Flegrei highlights the importance of accurate and continuous surveillance of volcanic gas emissions to support scientific interpretation and civil protection efforts. Suitable sensors capable of fast, real-time tracking of trace gas components within CO2-H2O -dominated fumarolic plumes are still missing. In this work, a compact Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS) sensor was used for real-time and in situ detection of the hydrogen sulfide (H2S) emitted from the Pisciarelli fumarolic field at the Campi Flegrei caldera. The 1 s response time of the sensor allows the capture of the fast emission dynamics of the plume and accurate reconstruction of H2S emission peaks up to 60 part-per-million (ppm). By combining the QEPAS measurements with a commercial non-dispersive infrared spectroscopy CO2 sensor, a characteristic CO2/H2S ratio of 208 ± 4 was estimated for the Pisciarelli fumarolic field.