Remote FTIR Research Articles

浅間山噴煙中の火山ガス化学組成の遠隔観測(＜特集＞2004年浅間山噴火(2))

浅間山噴煙中の火山ガス化学組成の遠隔観測(＜特集＞2004年浅間山噴火(2))

3-A07 遠隔FT-IR測定による昭和火口と南岳火口の火山ガスHCl/SO2比(桜島・霧島火山の活動2,口頭発表)

3-A07 遠隔FT-IR測定による昭和火口と南岳火口の火山ガスHCl/SO2比(桜島・霧島火山の活動2,口頭発表)

Chemical monitoring of volcanic gas using remote FT-IR spectroscopy at several active volcanoes in Japan

Abstract Chemical compositions of volcanic gases of several Japanese active volcanoes have been monitored from distant safe places since the beginning of the 1990s using an FT-IR spectral radiometer. For absorption measurements, an infrared light source behind volcanic gas emissions is necessary in a volcanic environment. In the early observations, infrared radiation from hot lava domes (Unzen volcano) and hot ground heated by high-temperature fumaroles (Usu, Aso, and Satsuma-Iwojima volcanoes) were used as infrared light sources. However, these sources were not available in many cases. This remote FT-IR method became more commonly applied to chemical monitoring of volcanic gases emitted from the summit or slopes of active volcanoes using scattered solar infrared light as infrared light sources (Sakurajima, Miyakejima, and Asama volcanoes). To date, eight species have been measured using this method: SO2, HCl, HF, CO, CO2, COS, SiF4, and H2O. The observations indicate that volcanic gases for each volcano have different chemical composition on a SO2–HCl–HF ternary diagram in spite of similar tectonic settings, suggesting that vapor/melt volume ratios during volcanic gas formation differ among volcanoes. During more than 15 years of monitoring, chemical changes in volcanic gases attributable to ascent of magma were observed only at Asama, where HCl/SO2 and HF/HCl ratios in the eruptive period were higher than those in non-eruptive period because of scrubbing of more soluble components in surface hydrothermal systems in the non-eruptive stage or solubility-controlled fractionation processes. Results show that these parameters are the most prospective ones among the various parameters measured using the remote FT-IR method to monitor volcanic activities.

Trend analysis of greenhouse gases over Europe measured by a network of ground-based remote FTIR instruments

Abstract. This paper describes the statistical analysis of annual trends in long term datasets of greenhouse gas measurements taken over ten or more years. The analysis technique employs a bootstrap resampling method to determine both the long-term and intra-annual variability of the datasets, together with the uncertainties on the trend values. The method has been applied to data from a European network of ground-based solar FTIR instruments to determine the trends in the tropospheric, stratospheric and total columns of ozone, nitrous oxide, carbon monoxide, methane, ethane and HCFC-22. The suitability of the method has been demonstrated through statistical validation of the technique, and comparison with ground-based in-situ measurements and 3-D atmospheric models.

Temporal variation in chemical composition of the volcanic plume from Aso volcano, Japan, measured by remote FT-IR spectroscopy

Remote measurements of chemical compositions of the Aso volcanic plume using an FT-IR spectral radiometer were carried out at the 1st crater of Mt. Nakadake, Aso volcano, Japan, for six times from 1996 to 2003. We have succeeded in detecting 6 volcanic gas species (SO2, HCl, HF, CO, CO2, COS) using the InSb detector. The equilibrium temperatures estimated from observed CO/CO2 ratios have remained high at more than 700°C during the observation period. However, the temporal variation of the ratios between volcanic gas components showed significant scrubbing of HCl compared to other species by hydrothermal interaction in 1998. From the visual and FT-IR observations, we presume that SO2 flux from the volcano was lower in 1998 than in other years. This decrease in flux was not due to hydrothermal scrubbing of SO2 but was due to decrease in a total supply rate of gas from depth. This assumption is supported by relatively stable CO2/SO2 ratio which is probably reflecting stable gas chemistry at the gas source.

High SiF4/HF ratio detected in Satsuma-Iwojima volcano’s plume by remote FT-IR observation

Remote FT-IR measurements of volcanic plume of Mt. Iwodake, Satsuma-Iwojima volcano, Japan, were carried out in October 1996 to understand plume chemistry of the volcano, especially characteristics of fluorine-bearing species in the plume. The SO2/HCl molar ratio in the plume was about 4, that is larger than the ratio in high-temperature gases. The high content of SO2 is suggested to be caused by sulfur combustion in the crater. An average SiF4/HF molar ratio of 0.57 was observed for the plume, which is about one order of magnitude higher than the previously reported ratio. The result shows that SiF4 is an important species and has similar to even larger contribution for fluorine output from Satsuma-Iwojima volcano than HF. The SiF4 flux of Satsuma-Iwojima volcano is about 13 t/d, that is the largest SiF4 flux from volcanoes in the world. The observed SiF4/HF ratio cannot be explained only by the high-temperature fumarolic composition of the volcano according to the thermodynamic calculations. The ratio can be explained if contribution of F-rich low-temperature fumaroles to the total gas flux of the volcano is as high as 40%.

Remote determination of SiF4 in volcanic plumes: A new tool for volcano monitoring

SiF4 is probably a common trace component of fumarole gases on volcanoes, arising from interactions between magmatic HF and wall rocks. It is not distinguished from HF in conventional analyses. A strong absorption band at 1032 cm−1 makes SiF4 well suited to remote open‐path FTIR spectroscopic techniques. We report the first measurements of SiF4 in volcanic gases at Etna and Vulcano (Sicily). SiF4 concentrations were low at Etna, but higher at Vulcano, where the SO2: SiF4 ratio was consistently around 1.7×10−2: 1. Thermodynamic considerations show that the HF : SiF4 ratio increases sharply with increasing temperature. Thus, remote measurements of SiF4 may offer a qualitative way of constraining fumarole temperatures. We use our FTIR measurements of HCl: SiF4 in combination with conventional measurements of HCl: HF to infer an HF :SiF4 ratio for Vulcano of ∼10:1, consistent with gas temperatures in the range 200–450°C.

The Spectral Characterizations of the Low and High Resolution Remote FTIR Emission Spectroscopy

Abstract The spectral characterizations of the flame combustion of the low and high spectral resolution remote Fourier transform infrared emission spectrometry have been investigated. This study has shown the high resolution FTIR spectroscopy has higher signal-to-noise ratio and detection sensitivity compared with the low resolution, and has measured accurately the frequency of each spectral line of the fine structures for the isotopic HCl35 and HCl37 bands at 2890 cm−1. We find that the separations of all the doublings of the isotopic HCl35 and HCl37 decrease with decreasing the line number m. Additionally, the aim of this paper is to select a suitable spectral resolution used in the analysis for obtaining a satisfactory result.

Real‐time monitoring of the cure reaction of a TGDDM/DDS epoxy resin using fiber optic FT‐IR

AbstractThe feasibility of using remote FT‐IR spectroscopy to monitor the gelation reaction of an epoxy resin used in advanced composite materials has been studied. The commercial epoxy resins MY720 and MY721, consisting mostly of tetraglycidyl 4,4′‐diaminodiphenyl methane (TGDDM) were cured with diaminodiphenylsulfone (DDS) in a microcapillary cell connected to an FT‐IR spectrometer by single silica fiber optics. By operating in the near‐IR, direct measurement of the consumption of epoxide and primary amine and growth in hydroxyl groups was possible. It was found that the primary amine band at 5067 cm−1 was the most sensitive for rapid and accurate real‐time monitoring of the cure reaction up to gelation. The temperature dependence of amine consumption from 135 to 180°C gave an activation energy of 70 kJ mol−1 for the cure reaction in agreement with DSC. Several artefacts involved in using fiber optic FT‐IR in this way have been identified.