REMOTE DETECTION OF HCL AND SO2 IN VOLCANIC GAS FROM UNZEN VOLCANO, JAPAN

A telescope-attached FT-IR spectral radiometer was applied for remote measurement of chemical composition of the volcanic gas of Unzen volca no, Japan, which started erupting in November 1990. The observations w ere carried out at the site about 1.3 km away from the gas-emitting re gion of the volcano in March and July 1992. Absorption features of SO2 (v1) and HCl were identified and column amounts of SO2 and HCl of the volcanic gas plume were estimated using a nonlinear least-squares met hod. The SO2/HCl ratio was in the range between 0.7 and 1.8 for both M arch and July observations. This is the first remote ground-based obse rvation of HCl in volcanic gas.