Field measurements of volcanic gases using tunable diode laser based mid-infrared and Fourier transform infrared spectrometers

Richter, Dirk; Erdélyi, Miklós; Curl, R. F.; Tittel, Frank K.; Oppenheimer, Clive; Duffell, H. J.; Burton, Mike

doi:10.1016/s0143-8166(01)00094-x

Cited by 56 publications

(33 citation statements)

References 16 publications

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“…A similar procedure has been commonly applied to the retrieval of gas concentrations from open path measurements of volcanic plumes (e.g. Oppenheimer et al, 1998;Horrocks et al, 1999 andRichter et al, 2002). The specific retrieval procedure used here is based on the Multi-Atmospheric Layer Transmission (MALT) model of Griffith (1996) and Griffith et al (2003), whose past applications include the analysis of open-path, White cell, and solar occultation spectra (Goode et al, 1999;Goode et al, 2000;Bertschi et al, 2003;Galle et al, 2000;Griffith et al, 2002).…”

Section: Spectrum Simulation and Fitting Algorithmmentioning

confidence: 99%

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO2, CH4 and CO over concentrations representative of "clean air" and "polluted plumes"

et al. 2011

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Abstract. When compared to established point-sampling methods, Open-Path Fourier Transform Infrared (OP-FTIR) spectroscopy can provide path-integrated concentrations of multiple gases simultaneously, in situ and near-continuously. The trace gas pathlength amounts can be retrieved from the measured IR spectra using a forward model coupled to a non-linear least squares fitting procedure, without requiring "background" spectral measurements unaffected by the gases of interest. However, few studies have investigated the accuracy of such retrievals for CO 2 , CH 4 and CO, particularly across broad concentration ranges covering those characteristic of ambient to highly polluted air (e.g. from biomass burning or industrial plumes). Here we perform such an assessment using data collected by a field-portable FTIR spectrometer. The FTIR was positioned to view a fixed IR source placed at the other end of an IR-transparent cell filled with the gases of interest, whose target concentrations were varied by more than two orders of magnitude. Retrievals made using the model are complicated by absorption line pressure broadening, the effects of temperature on absorption band shape, and by convolution of the gas absorption lines and the instrument line shape (ILS). Despite this, with careful model parameterisation (i.e. the optimum wavenumber range, ILS, and assumed gas temperature and pressure for the retrieval), concentrations for all target gases were able to be retrieved to within 5%. Sensitivity to the aforementioned model inputs was also investigated. CO retrievals were shown to be Correspondence to: T. E. L. Smith (thomas.smith@kcl.ac.uk) most sensitive to the ILS (a function of the assumed instrument field-of-view), which is due to the narrow nature of CO absorption lines and their consequent sensitivity to convolution with the ILS. Conversely, CO 2 retrievals were most sensitive to assumed atmospheric parameters, particularly gas temperature. Our findings provide confidence that FTIRderived trace gas retrievals of CO 2 , CH 4 and CO based on modeling can yield results with high accuracies, even over very large (many order of magnitude) concentration ranges that can prove difficult to retrieve via standard classical least squares (CLS) techniques. With the methods employed here, we suggest that errors in the retrieved trace gas concentrations should remain well below 10%, even with the uncertainties in atmospheric pressure and temperature that might arise when studying plumes in more difficult field situations (e.g. at uncertain altitudes or temperatures).

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Section: Spectrum Simulation and Fitting Algorithmmentioning

confidence: 99%

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO2, CH4 and CO over concentrations representative of "clean air" and "polluted plumes"

et al. 2011

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“…Depending on which thermal IR band is chosen, additional complications can arise from interference by pressure-broadened absorption lines of other atmospheric compounds (mainly CO 2 and H 2 O). Therefore, IR laser absorption measurements of SO 2 are usually performed in cells at reduced barometric pressures (Richter et al, 2002;Rawlins et al, 2005), and no IR laser absorption measurements of SO 2 along open atmospheric paths are known to date. In the absence of an SO 2 measurement, emission rates of gases detected using NIR-TDLAS cannot easily be determined using the ratio method described earlier.…”

Section: F Vita Et Al: Development Of a Portable Active Lp-doasmentioning

confidence: 99%

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

Vita

Kern

Inguaggiato

2014

J. Sens. Sens. Syst.

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Abstract. Active long-path differential optical absorption spectroscopy (LP-DOAS) has been an effective tool for measuring atmospheric trace gases for several decades. However, instruments were large, heavy and powerinefficient, making their application to remote environments extremely challenging. Recent developments in fibre-coupling telescope technology and the availability of ultraviolet light emitting diodes (UV-LEDS) have now allowed us to design and construct a lightweight, portable, low-power LP-DOAS instrument for use at remote locations and specifically for measuring degassing from active volcanic systems. The LP-DOAS was used to measure sulfur dioxide (SO 2 ) emissions from La Fossa crater, Vulcano, Italy, where column densities of up to 1.2 × 10 18 molec cm −2 (∼ 500 ppmm) were detected along open paths of up to 400 m in total length. The instrument's SO 2 detection limit was determined to be 2 × 10 16 molec cm −2 (∼ 8 ppmm), thereby making quantitative detection of even trace amounts of SO 2 possible. The instrument is capable of measuring other volcanic volatile species as well. Though the spectral evaluation of the recorded data showed that chlorine monoxide (ClO) and carbon disulfide (CS 2 ) were both below the instrument's detection limits during the experiment, the upper limits for the X / SO 2 ratio (X = ClO, CS 2 ) could be derived, and yielded 2 × 10 −3 and 0.1, respectively. The robust design and versatility of the instrument make it a promising tool for monitoring of volcanic degassing and understanding processes in a range of volcanic systems.

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“…A precise measurement conducted with mid-IR OPO of the ratio of the two stable carbon isotopes of CO 2 ( 13 CO 2 and 12 CO 2 ) can provide valuable information about CO 2 exchange processes in the volcanic plume. 106,107 The invention of the femtosecond frequency comb really made revolutions in the field of spectroscopy. Besides the newly developed techniques discussed above, dual frequency comb spectroscopy (DFCS) emerges as a promising, highly sensitive, and superior fast spectroscopy with high resolution to complement the traditional Fourier transform spectroscopy (FTS).…”

Section: Architecture Of Opomentioning

confidence: 99%

Developments of mid-infrared optical parametric oscillators for spectroscopic sensing: a review

Peng¹

2014

Opt. Eng

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Abstract. Optical parametric oscillator is an attractive way of generating tunable mid-infrared light in the spectral range where lasers simply do not exist-for the needs of spectroscopy, medical applications, remote sensing, etc. We will go through the fundamentals of the optical parametric oscillator first and then introduce the related new phase-matching, cavity design, and spectroscopic techniques.

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Field measurements of volcanic gases using tunable diode laser based mid-infrared and Fourier transform infrared spectrometers

Cited by 56 publications

References 16 publications

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of "clean air" and "polluted plumes"

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of "clean air" and "polluted plumes"

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

Developments of mid-infrared optical parametric oscillators for spectroscopic sensing: a review

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Field measurements of volcanic gases using tunable diode laser based mid-infrared and Fourier transform infrared spectrometers

Cited by 56 publications

References 16 publications

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and CO over concentrations representative of &quot;clean air&quot; and &quot;polluted plumes&quot;

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and CO over concentrations representative of &quot;clean air&quot; and &quot;polluted plumes&quot;

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

Developments of mid-infrared optical parametric oscillators for spectroscopic sensing: a review

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Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of "clean air" and "polluted plumes"

Absolute accuracy and sensitivity analysis of OP-FTIR retrievals of CO<sub>2</sub>, CH<sub>4</sub> and CO over concentrations representative of "clean air" and "polluted plumes"