ABSTRACT

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.