Concentrations Of Multiple Gases Research Articles

Mass spectrometric multiple soil-gas flux measurement system with a portable high-resolution mass spectrometer (MULTUM) coupled to an automatic chamber for continuous field observations

Abstract. We developed a mass spectrometric soil-gas flux measurement system using a portable high-resolution multi-turn time-of-flight mass spectrometer, called MULTUM, and we combined it with an automated soil-gas flux chamber for the continuous field measurement of multiple gas concentrations with a high temporal resolution. The developed system continuously measures the concentrations of four different atmospheric gases (NO2, CH4, CO2, and field soil–atmosphere flux measurements of greenhouse gases (NO2, O2) ranging over 6 orders of magnitude at one time using a single gas sample. The measurements are performed every 2.5 min with an analytical precision (2 standard deviations) of ±34 ppbv for NO2; ±170 ppbv, CH4; ±16 ppmv, CO2; and ±0.60 vol %, O2 at their atmospheric concentrations. The developed system was used for the continuous field soil–atmosphere flux measurements of greenhouse gases (NO2, CH4, and CO2) and O2 with a 1 h resolution. The minimum quantitative fluxes (2 standard deviations) were estimated via a simulation as 70.2 µgNm-2h-1 for NO2; 139 µgCm-2h-1, CH4; 11.7 mg C m−2 h−1, CO2; and 9.8 g O2 m−2 h−1, O2. The estimated minimum detectable fluxes (2 standard deviations) were 17.2 µgNm-2h-1 for NO2; 35.4 µgCm-2h-1, CH4; 2.6 mg C m−2 h−1, CO2; and 2.9 g O2 m−2 h−1, O2. The developed system was deployed at the university farm of the Ehime University (Matsuyama, Ehime, Japan) for a field observation over 5 d. An abrupt increase in NO2 flux from 70 to 682 µgNm-2h-1 was observed a few hours after the first rainfall, whereas no obvious increase was observed in CO2 flux. No abrupt NO2 flux change was observed in succeeding rainfall events, and the observed temporal responses at the first rainfall were different from those observed in a laboratory experiment. The observed differences in temporal flux variation for each gas component show that gas production processes and their responses for each gas component in the soil are different. The results of this study indicate that continuous multiple gas concentration and flux measurements can be employed as a powerful tool for tracking and understanding underlying biological and physicochemical processes in the soil by measuring more tracer gases such as volatile organic carbon, reactive nitrogen, and noble gases, and by exploiting the broad versatility of mass spectrometry in detecting a broad range of gas species.

Design of a six-gas NDIR gas sensor using an integrated optical gas chamber.

A non-dispersive infrared (NDIR) gas sensor with an integrated optical gas chamber was designed to accurately detect multiple gas concentrations in a complex polluted environment. This chamber consists of a hexagonal prism shell and a reflection plate. In particular, six dual-channel infrared detectors for sensing different gases and one collimated infrared light source are integrated in the gas chamber. The IR light emitted by the collimated IR light source arrives at these detectors after four reflections. The result of simulation and data collection for optical path length and luminous flux shows that the average optical path length in the chamber is 63 mm, and the effective utilization rate of the luminous flux can reach 78.8%. The highly compact NDIR sensor can detect the concentrations of a mixture of gases (CO, CO2, CH4, H2CO, NH3, and NO with a volume fraction ranging from 0 to 4%).

Simultaneous detection of multiple gas concentrations with multi-frequency wavelength modulation spectroscopy

A multi-frequency wavelength modulation spectroscopy (MF-WMS) method for simultaneous monitoring multiple gas concentrations is reported. Two wavelength lasers are selected and scanned at the same sawtooth waveform and different sinusoidal modulation frequencies. Also, a 2-in-1 coupler is used to collect laser beams into a single-mode fiber to deliver the combined beams to a same optical path. The outputs from the same InGaAs detector are demodulated by a set of homemade digital lock-in-amplifiers to obtain the harmonic signals, accordingly. The new multi-pass cell was designed and filled with five different concentrations of H2S and HCl gas mixtures for further analysis. In addition, an digital filter and a data running means method were used to further improve the stability. The results show that the signal-to-noise ratio and the anti-interference ability had been improved and the MF-WMS system gives a good performance in terms of reproducibility and feasibility.

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"

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 CO2, CH4 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 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, CO2 retrievals were most sensitive to assumed atmospheric parameters, particularly gas temperature. Our findings provide confidence that FTIR-derived trace gas retrievals of CO2, CH4 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).

Commentary on Viewpoint “Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law”

LETTERS TO THE EDITORCommentary on Viewpoint “Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law”H. D. Van Liew, and E. T. FlynnH. D. Van Liew, and E. T. FlynnPublished Online:01 Apr 2007https://doi.org/10.1152/japplphysiol.00055.2007MoreSectionsPDF (24 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat to the editor: Arieli (1) draws attention to experiments showing that solubility of individual gases may be reduced when high concentrations of multiple gases are present simultaneously. Results with in vitro systems of ethanol and water may not be representative of gases in tissue; for example, metabolism of oxygen will lower the oxygen partial pressure far below the inhaled value so tissue may still behave as a one-gas system despite a high inspired partial pressure of oxygen.The underlying mechanisms of bubble formation in divers, aviators, or astronauts who suffer decompression sickness (DCS) are poorly understood. It is suspected that DCS bubbles are generated from semi-permanent gaseous micronuclei. Gas diffusing into a micronucleus to initiate a bubble may be more closely related to gas partial pressure than to dissolved gas, but the final size of a bubble, if it does form, is probably related to dissolved gas. Interaction among the gases inside a bubble effects inward diffusion, an additional complication to breathing of gas mixtures (2).There is considerable difference of opinion about what constitutes successful decompression, as evidenced by the differences between instructions used by several of the world's navies (3). Also one must be cautious when interpreting the self-reported safety data collected by the Diver's Alert Network. The effect of one gas on the solubility of another may ultimately be shown to be an important factor in decompression, but, at present, we regard it as just one uncertainty among a great many other uncertainties.REFERENCES1 Arieli R. Heliox, nitrox, and trimix diving; hyperbaric oxygen treatment; and a flaw in Henry's law. J Appl Physiol. In press.Google Scholar2 Van Liew HD, Burkard ME. Breathing a mixture of inert gases: disproportionate diffusion into decompression bubbles. Undersea Hyperbaric Med 23: 11–17, 1996.Google Scholar3 Van Liew HD, Flynn ET. Decompression tables and dive-outcome data: graphical analysis. Undersea Hyperbaric Med 32: 187–198, 2005.Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: H. D. Van Liew, 100 Goodview Way, Barnstable, MA 02630 Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation More from this issue > Volume 102Issue 4April 2007Pages 1721-1721 Copyright & PermissionsCopyright © 2007 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00055.2007PubMed17409298History Published online 1 April 2007 Published in print 1 April 2007 Metrics

In-situ laser spectroscopy of CO, Ch4, and H2O in a particle laden laboratory-scale fluidized bed combustor

The pyrolysis, devolatilization and char combustion of bituminous coal and biomass (beechwood, firwood) were investigated in a laboratory-scale fluidized bed combustor by tunable diode laser spectroscopy. Individual fuel particles were suspended in the freeboard of the unit. The bed temperature was 800 ?C, the oxygen partial pressure 0 to 20 kPa (0-10 vol.%). Two Fabry Perot type tunable near infrared diode lasers were deployed for quantitative in-situ species concentration measurements. CH4 and CO were measured simultaneously during devolatilization and char combustion in-situ 10 mm above the surface of the fuel particles as well as H2O using laser spectroscopy. Sand particles were passing the probing laser beam path. Besides the resonant absorption of the laser light by CO, CH4 and H2O severe and strongly transient non-resonant attenuation by partial blocking of the beam and beam steering effects occurred. By wavelength tuning the two laser sources, species concentrations could be determined. The measured absorbances had to be corrected for the real temperature measured at the position of the probing laser beam. In addition, CO, CO2 and O2 were determined ex-situ by con ventional methods. A spatial profile inside the FBC of major species (CH4, CO, CO2, O, H, OH) was calculated using a chemical kinetics program for a single fuel particle in a plug flow reactor geometry. The results were compared to the experimental findings. Good agreement was found. Tunable diode laser spectroscopy was found to be an apt method of determining quantitative species concentrations of multiple gases in a high temperature multi phase environment.

Infrared absorption spectroscopy for monitoring condensible gases in chemical vapor deposition applications

In situ infrared absorption spectroscopy is used to monitor the delivery of condensible gases in chemical vapor deposition (CVD) systems. A Fourier transform infrared (FTIR) spectrometer has been configured to enable simultaneous measurements of the concentrations of multiple gases which are critical to the performance of CVD processes. In the deposition of silicon dioxide (SiO2) films using tetraethylorthosilicate (TEOS) and ozone (O3), IR measurements of the concentration of gas-phase TEOS closely track the deposition rate of SiO2. In doped oxide deposition processes, the percentage of phosphorous in the film is predicted from infrared measurements of the concentration of the dopant precursor gas [trimethylphosphene (TMP)]. These capabilities provide improved control of the delivery of condensible gases in CVD systems without the use of test wafers, and they enable the detection of failures in the gas delivery system in real time.