Remote detection of fumarolic gas chemistry at Vulcano, Italy, using an FT-IR spectral radiometer

An infrared absorption spectroscopy remote sensing technique was used to determine the SO2/HCl ratio in fumarolic plumes at Vulcano, Italy. The measurements were made from the southern crater rim of Fossa Grande Crater, about 400 m from the fumarolic area in the crater. Infrared absorption spectra of HCl and SO2 were observed for four fumaroles a few tens of metres apart using the hot fumarolic surface as an infrared light source. The measured SO2/HCl ratios in the FA, F47, FW and lower parti of the F21 fumaroles were 4.5–5.4, 3.5, 9.5–11.2 and 5.8 respectively. The SO2/HCl ratio of the FA fumarole was higher than that of the gas collected directly in the fumarolic vent (SO2/HCl ratio = 2.9), and was closer to the S(total)/HCl ratio (= 4.6) of the collected gas. Our results show that the SO2/HCl ratios of two fumaroles only a few tens of metres apart exhibits differences of about twofold. This suggests that this remote monitoring technique is capable of detecting spatial distribution in the SO2/HCl ratios of volcanic plumes. Because temporal variations in S/Cl ratios can provide precursory signals for volcanic eruptions [1–3], this remote sensing technique can used efficiently for evaluation of volcanic activity.