Long-Term and Mobile Monitoring of Atmospheric Sulfur Dioxide and Hydrogen Sulfide at Mt. Aso and Kumamoto City

Flow analysis was applied to atmospheric analyses, and its usefulness and reliability were examined through a long-term measurement.The analysis system was comprised of small diffusion scrubbers and homemade fluorescence and conductivity detectors to measure H2S and SO2.The systems were settled in Kumamoto city and Mt.Aso, and the gases were monitored for two and a half years.We also brought this system to Aso crater, to walk around with, and investigated the gas distributions.Based on the gas data obtained at the two locations, the gas behaviors were investigated.The daily variations of SO2 and H2S were opposite, and the effects from the wind of the two gases were also different.The volcanic activity greatly affected the gas levels.In the active period, the SO2 gas level and the gas ratio of SO2/H2S became high.Near the fumaroles, the gas levels changed by 3 or 4 orders in a very short time.At 1 km downstream of the wind from the crater, the H2S ratio was much lower, which indicated that H2S decomposition occurred in a short time.