Continuous in-situ measurements of gases (H2, H2S, CH4, N2, O2, He and CO2) at the fumarole “Soffionissimo” (Solfatara volcano, Southern Italy).

Abstract

Temperature measurements and gas extraction were done at the fumarole very close to the “Bocca Grande”. The temperature measurements were performed with a temperature probe (K-type thermocouple), which was let about 30 cm into the fumarole. For better comparison of temperature and gas data, the gas tube was directly connected with the temperature probe, to make sure that temperature measurement and gas extraction were carried out at the same place. After having adjusted a continuous gas flow with diaphragm pump and a needle valve, the gas was piped through a 10 m Teflon© tube for more than 40 hours. The gas phase primary consists of water gas, which was condensed in a trap, installed in a refrigerator. The amount of water in the trap was determined in regular intervals (every 3-4 hours). At the beginning of the monitoring experiment, the Teflon© tube was heated in order to avoid condensation of the water in the tube before getting trapped. Although the tube was not heated for the whole time of the experiment, it turns out that the amount of water, condensed in the water trap per hour, does not significantly change when the tube was not heated. Hence, the amount of water, condensing in the tube before getting trapped, seems negligible. The remaining, almost water-free gas phase was finally dried over Fe in a filter, and then continuously analysed with a quadrupole mass spectrometer (Balzers Omnistar) for the following components: H2, H2S, CH4, N2, O2, Ar, He, and CO2. To make sure that the final drying process does not influence the gas composition in particular for H2 and H2S, a comparison measurement was done without the filter, which only revealed somewhat higher water content. During the second half of the monitoring, additionally a laser-optical CO2 sensor was installed (not shown in the sketch). Gas samples were taken from the gas line for laboratory gas-chromatographic analysis.