We have determined SO2 concentration in fumarolic gas released from the summit crater of Asama volcano, Japan, using an infrared spectral radiometer installed in a site about 4 km away from the summit. During the observation period from 31 October to 4 November 1991, weak fumarolic activities with a height less than 100 m were observed intermittently. The infrared spectrum of the fumarolic gas just above the summit showed slight absorption due to rotational bands associated with v, vibration (1151 cm–1) of the SO2 molecule. Compared with the spectrum of standard SO2 gas, this absorption corresponds roughly to the column amount of 250 ppm-m SO2. This is the first result of remote detection of SO2 in volcanic gas from a ground station by means of infrared spectroscopy. Infrared spectral radiometer is a promising tool for remote detection of various chemical species in volcanic gas.
Geochemical Society of Japan