HR: 0800h
AN: V21E-0659    [Abstracts]
TI: Recent Advances of Portable Multi-Sensor Technique of Volcanic Plume Measurement
AU: * Shinohara, H
EM: shinohara-h@aist.go.jp
AF: Geological Survey of Japan, AIST, Higashi 1-1-1, Central ', Tsukuba, 305-8567 Japan
AB: A technique has been developed to estimate chemical composition volcanic gases based on the measurement of volcanic plumes at distance from a source vent by the use of a portable multi-sensor system consisting a humidity sensor, an SO₂ electrochemical sensor and a CO₂ IR analyzer (Shinohara, 2005). Since volcanic plume is a mixture of the atmosphere and volcanic gases, the volcanic gas composition can be estimated by subtracting the atmospheric background from the plume data. This technique enabled us to estimate concentration ratios of major volcanic gas species (i.e., H₂O, CO₂ and SO₂) without any complicated chemical analyses even for gases emitted from an inaccessible open vent. Since the portable multi-sensor system was light (~ 5 kg) and small enough to carry in a medium size backpack, we could apply this technique to measure volcanic plumes at summit of various volcanoes including those which require us a tough climbing, such as Villarrica volcano, Chile. We further improved the sensor system and the measurements techniques, including application of LI-840 IR H₂O and CO₂ analyzer, H₂S electrochemical sensor and H2 semi-conductor sensor. Application of the new LI-840 analyzer enabled us to measure H₂O concentration in the plume with similar response time with CO₂ concentration. The H₂S electrochemical sensor of Komyo Co. has a chemical filter to removed SO2 to achieve a low sensitivity (0.1%) to SO₂, and we can measure a high SO₂/H₂S ratio up to 1000. The semi-conductor sensor can measure H₂ concentration in the range from the background level in the atmosphere (~0.5 ppm) to ~50 ppm. Response of the H₂ sensor is slower (90% response time = ~90 sec) than other sensors in particular in low concentration range, and the measurement is still semi-quantitative with errors up to ±50%. The H₂/H₂O ratios are quite variable in volcanic gases ranging from less than 10^-5 up to 10^-1, and the ratio is largely controlled by temperature and pressure condition of the internal equilibrium. In particular, we can calculate the equilibrium condition for the reaction (SO₂ + 3H₂ = 2H₂O + H₂S) based on the results of the plume measurements by the portable multi-sensor technique.
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8419 Volcano monitoring (7280)
DE: 8430 Volcanic gases
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005