Fumarole compositions and mercury emissions from the Tatun Volcanic Field, Taiwan: Results from multi-component gas analyser, portable mercury spectrometer and direct sampling techniques

Abstract

Gas emissions from Tatun volcanic group, northern Taiwan, were studied for the first time using a multi-component gas analyser system (Multi-GAS) in combination with Giggenbach flask methods at fumaroles and mud pools at Da-you-keng (DYK) and Geng-tze-ping (GZP). CO 2/S molar ratios observed at DYK ranged from 3–17, similar ratios were observed using a Multi-GAS sensor box of 8–16. SO 2 at GZP was low, higher concentrations were observed at DYK where SO 2/H 2S ratios were close to 1 for both methods. A lower CO 2/H 2S ratio was measured via Giggenbach flask sampling (7.2) than was found in the plume using the gas sensor at GZP (9.2). This may reflect rapid oxidation of H 2S as it mixes with background air. Gaseous elemental mercury (GEM) levels were observed in the fumarole gases using a portable mercury spectrometer. These are the first such measurements of mercury at Tatun. Mean GEM concentrations in the fumarole plumes were ∼ 20 ng m − 3 , with much higher concentrations observed close to the ground (mean [GEM] 130 and 290 ng m − 3 at DYK and GZP, respectively). The GEM in the fumarole plume was elevated above concentrations in industrial/urban air in northern Taiwan and the increase in GEM observed when the instrument was lowered suggests high levels of mercury are present in the surrounding ground surface. The GEM/CO 2 (10 − 8 ) and GEM/S (10 − 6 ) ratios observed in the fumarole gases were comparable to those observed at other low-temperature fumaroles. Combining the Hg/CO 2 ratio with a previous CO 2 flux value for the area, the annual GEM flux from the Tatun field is estimated as 5–50 kg/year.