Study on Chemical Monitoring of Volcanic gas using an IR spectroscopy

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1. I have developed a remote detection system of chemical components in volcanic gas, on the basis of infrared (IR) spectroscopy. The IR light which had passed through the volcanic gas was collected with a Cassegrainian telescope and was introduced into an FT-IR spectrometer.2. The measurements were carried out at Unzen, Kirishima, Aso, Sakurajima and Asama volcanoes, Japan, and also at Vulcano volcano, Itary.3. It is found that IR absorption spectra of chemical components were obtained, when IR source is naturally available behind the volcanic gas. In the case of Unzen volcano, absorption spectra of HC1 and SO2 were clearly identified using IR emission from hot lava dome behind the volcanic gas as an IR light source. This is first remote detection of HC1 in volcanic gas. In order to estimate the column amount of HC1 and SO2 from the observed spectra, a non-linear least-square method was applied, and then SO2/HC1 ratios of volcanic gas were calculated. The results shows that this remote monitoring technique is capable of detecting temporal change in the SO2/HCl ratios of volcanic gases emmitting far away from the observation site. In the case of Aso volcano, hot water standing on the bottom of the summit crater could be used as an IR light source, and absorption spectra of volcanic gas filling the crater were observed. At Vulcano volcano, Italy, the hot ground surface of the fumarolic area could be used as an IR light source, and spatial distribution in the SO2/HCl ratios of volcanic gas was detected.4. In general, chemical compositions of volcanic gas change after releasing into the atmosphere, bacause oxidations of the gas proceed in the atmosphere. The conversion of H2S to SO2 was experimentally checked. Therefore, it is suggested that SO2 detected in this remote monitoring includes original SO2 in the fumarole and SO2 derived from oxidation of H2S in the atmosphere.