Giggenbach bottle technique is used to systematically analyze fumarolic gas composition of the Tatun Volcano Group, northern Taiwan. The area is quite active hydrothermally and is also considered volcanically active. The gas composition of fumarolic samples is predominantly steam water with CO2 as the dominant component after de-watering. Minor components include sulfur species (mainly H2S and SO2), N2 and CH4 . Interestingly, in the study area, H2S concentration is always much higher than SO2 for all measured fumarolic gases. This result resembles the typical composition of low temperature fumaroles, when comparisons are made on a worldwide basis.
Hsiao-you-keng and Liou-huang-ku were selected as testing sites to discuss factors pertaining to weather and sampling time as these may affect fumarolic gas composition. Test results show that the length of sampling time in this area mainly depends on the saturation of alkali solution. Furthermore, based on continuous data, gas composition of fumaroles seems not to be affected by weather factors. This implies that the de-gassing system in the Tatun volcanic area is quite steady and generated no significant variation in gas composition during the study period. These results indicate that current sampling and analytical procedures are suitable for volcanic gas study and further surveillance in the Tatun volcanic area.