Isotopic fractionation of SO2 and H2S gases during the absorption by KOH solution, with the application to volcanic gas monitoring at Miyakejima Island, Japan

摘要

The chemical trap method has been used for monitoring of volcanic activity. In this method, a strong alkaline water solution was exposed in ambient air. Acidic gases, such as SO2, H2S, HCl and HF are absorbed in KOH solution without any instrumental support. For sulfur isotopic monitoring with this method, however, a sulfur isotopic fractionation between fumarolic gas and sulfur trapped in KOH solution occurs (Sakai and Ueda, 1984). In this study, the magnitude of isotopic fractionation was experimentally determined for SO2 and H2S gases. The δ34S of SO2 and H2S gases absorbed by KOH solution is, respectively, 2.4 and 6.5‰ lower than the gases in air, which agreed with the theoretical prediction based on molecular diffusion of SO2 and H2S in air.