Long-term continuous monitoring of the dissolved CO2 performed by using a new device in groundwater of the Mt. Etna (southern Italy)

We present a new device for continuous monitoring of the concentration of CO2 dissolved in water. The device consists of a tube made of a polymeric semi-permeable membrane connected to an infrared gas analyser (IRGA) and a pump. Several laboratory experiments were performed to set the best operating condition and test the accuracy of measurements. We used the device for performing 20 months of continuous monitoring of dissolved CO2 concentration (DCC) in groundwater within a drainage gallery at Mt. Etna. The monitored groundwater intercepts the Pernicana Fault, along which degassing is observed related to volcano-tectonic activity. The acquired data were compared with continuous and discrete data obtained using existing methods. The measurements of DCC resulted in some period of the year well correlated with air temperature. We also found that long-term trends, as well as short-term variations, are probably linked to the dynamics of volcanic activity and/or perturbations in the local or regional stress fields.

► New device for continuous monitoring of dissolved CO2 based on the use of a semi-permeable membrane. ► Tests for checking the optimal operating conditions and the accuracy of the measurements. ► Data acquired, in continuous and remote setting, for 20 months in groundwater of Mt. Etna (Italy). ► Comparison with continuous and discrete data obtained using existing methods. ► Identification of variations due to air–water gas exchange and seismo-volcanic processes.