Field Instrument for Simultaneous Large Dynamic Range Measurement of Atmospheric Hydrogen Sulfide, Methanethiol, and Sulfur Dioxide

摘要

We describe a membrane-based collection/analysis system that differentially monitors H{sub}2S and CH{sub}3SH, and to which a conductometric SO{sub}2 analyzer using the same collector was coupled. A diffusion scrubber (DS) comprised of a Nafion tube collects H{sub}2S selectively while a porous poly-tetrafluoroethylene (pPTFE) DS collects both H{sub}2S and CH{sub}3SH. Both gases are measured via their ability to react with fluorescein mercuric acetate (FMA) which results in decreased fluorescence. The limited dynamic range of a negative signal procedure was overcome by using dual DS units comprised of short and long scrubbers, placed serially in the liquid flow line. Different DS designs and membrane materials were investigated. H{sub}2S, CH{sub}3SH, and SO{sub}2 from a biogenic point source were continuously measured, and the H{sub}2S/CH{sub}3SH data compared well with a standard procedure involving Tedlar bag collection, preconcentration and thermal desorption from a Tenax trap, and measurement by gas chromatography/flame photometric detection. Walkaround portability of the instrument and very large dynamic range measurement of H{sub}2S and SO{sub}2 were demonstrated around the Mt. Aso volcano.