Methane Measurements Research Articles

A case study of a gravity wave induced by Amazon forest orography and low level jet generation

We investigated the role of turbulent coherent structures (CS), gravity waves (GW) and low-level jet (LLJ) propagation in the flow dynamics of the Nocturnal Boundary Layer (NBL) within and above a forest canopy at the Amazon Tall Tower Observatory (ATTO), in Central Amazon. Seven levels of wind velocity and temperature measurements allowed the study of the flow structure below and above the surface layer. We analyzed one dynamically rich night in 2015, which includes three distinct periods. In the first one, the NBL is characterized by CS generated at the canopy top. In the second period, the change in wind direction triggers the onset of a orographic GW above the roughness sublayer. The wave, suppressing the propagation of CS, strongly influences the boundary layer structure, both above and below the canopy. In the third period, low turbulence intensity at the canopy top enables the development of a LLJ. As the jet shear layer propagates upward, it disrupts the wave oscillations, while LLJ dominates the flow dynamics. The wavelet analyses identified i) turbulent and non-turbulent structures with different length and time-scales; ii) coupling of the flow at different levels and the vertical propagation of turbulent and wave motions; and iii) the ability of turbulent and low frequency processes associated with the orographic GW to penetrate within the canopy. Further, scalar measurements of methane, carbon monoxide and carbon dioxide identified the LLJ nose as upward limit for how far scalars can be transported.

Comparison of two gas volume measurement systems by evaluating biochemical methane potential

AbstractThe objective of this study is to compare and analyze the efficiency of an automated measurement system for biogas flow with a control performed by a programmable logic controller (PLC) called the SAMB compared to commercial equipment widely disseminated for this purpose, the automatic methane potential test system (AMPTS II). The objective is to identify the accuracy in gas flow analysis of the two systems. The experiments were conducted in triplicate at a constant temperature of 37°C in anaerobic reactors. Two synthetic substrates and two natural substrates combined with a microbial inoculum were used. Considering the different ways the two systems capture data, the results show that all samples differed statistically between them (p < 0.01) in each system. However, in relation to paired substrates between systems, the samples did not present statistically significant differences (p > 0.05). Thus, with the advancement and globalization of knowledge, it is necessary to develop systems capable of generating standardized, precise, and accurate data. In this context, the systems evaluated here present different forms of methane measurement but the results have no significant statistical differences.

High-speed supercontinuum laser absorption spectroscopy of light hydrocarbons in elevated pressures and temperatures

10 kHz near-infrared supercontinuum laser absorption spectroscopy measurements of methane (CH4) and acetylene (C2H2) were demonstrated. Measured absorption spectra were processed using the HITRAN database to infer species concentrations and temperatures. High pressure and high temperature measurements up to 10 bar and 800 K, respectively, were made in dedicated optical cells. Reacting flow field was also probed over a 6 cm flat flame burner. Due to the very short pathlength over the burner surface, a toroidal multipass reflection cell was used to maximize measurement sensitivity. The multipass cell was designed specifically to withstand high temperature environment around the flat flame burner and supported multiple beam pathlength configurations. The beam paths within the cell exist on a thin plane and were used to measure temperatures at various heights above the burner surface. Despite relatively low signal-to-noise ratio at higher temperature environments, species concentration predictions agreed well with experiment conditions. Temperature results agreed well with simulated results to within 20.2 K in the preheat zone of a methane–air flame.

Day-night differences in Mars methane suggest nighttime containment at Gale crater

We report new measurements of atmospheric methane by the Curiosity rover’s Tunable Laser Spectrometer that is part of the Sample Analysis at Mars suite (TLS-SAM), finding nondetections during two daytime measurements of average value 0.05 ± 0.22 ppbv (95% confidence interval CI). These are in marked contrast with nighttime background levels of 0.52 ± 0.10 (95% CI) from four measurements taken during the same season of northern summer. This large day-night difference suggests that methane accumulates while contained near the surface at night, but drops below TLS-SAM detection limits during the day, consistent with the daytime nondetection by instruments on board the ExoMars Trace Gas Orbiter. With no evidence for methane production by the rover itself, we propose that the source is one of planetary micro-seepage. Dynamical modeling indicates that such methane release is contained within the collapsed planetary boundary layer (PBL) at night due to a combination of nocturnal inversion and convergent downslope flow winds that confine the methane inside the crater close to the point where it is released. The methane abundance is then diluted during the day through increased vertical mixing associated with a higher altitude PBL and divergent upslope flow that advects methane out of the crater region. We also report detection of a large spike of methane in June 2019 with a mean in situ value over a two-hour ingest of 20.5 ± 4 ppbv (95% CI). If near-surface production is occurring widely across Mars, it must be accompanied by a fast methane destruction or sequestration mechanism, or both.

The Biophysical Role of Water and Ice Within Permafrost Nearing Collapse: Insights From Novel Geophysical Observations

AbstractThe impact of permafrost thaw on hydrologic, thermal, and biotic processes remains uncertain, in part due to limitations in subsurface measurement capabilities. To better understand subsurface processes in thermokarst environments, we collocated geophysical and biogeochemical instruments along a thaw gradient between forested permafrost and collapse‐scar bogs at the Alaska Peatland Experiment site near Fairbanks, Alaska. Ambient seismic noise monitoring provided continuous high‐temporal resolution measurements of water and ice saturation changes. Maps of seismic velocity change identified areas of large summertime velocity reductions nearest the youngest bog, indicating potential thaw and expansion at the bog margin. These results corresponded well with complementary borehole nuclear magnetic resonance measurements of unfrozen water content with depth, which showed permafrost soils nearest the bog edges contained the largest amount of unfrozen water along the study transect, up to 25% by volume. In situ measurements of methane within permafrost soils revealed high concentrations at these bog‐edge locations, up to 30% soil gas. Supra‐permafrost talik zones were observed at the bog margins, indicating talik formation and perennial liquid water may drive lateral bog expansion and enhanced permafrost carbon losses preceding thaw. Comparison of seismic monitoring with wintertime surface carbon dioxide fluxes revealed differential responses depending on time and proximity to the bogs, capturing the controlling influence of subsurface water and ice on microbial activity and surficial emissions. This study demonstrates a multidisciplinary approach for gaining new understanding of how subsurface physical properties influence greenhouse gas production, emissions, and thermokarst development.

Developing low-cost methane gas concentration measuring device

In every aspect of Engineering more advanced, efficient and progressive solutions are required. The modern age of science requires innovative minds. The field of environmental engineering is also advancing with modern science and technology innovations. Measuring of methane concentration and flow rate is nothing new, yet a complicated process. The need for more accurate measurement is a necessity in proper operation of bio digesters for methane generation. The traditional process of the measuring methane content in biogas is time consuming yet complicated. The need for development and application of methane measurement techniques is not only limited to biogas but has other monitoring value as well in other health and safety applications in built environments. Winsen Electronics and Hanwei Electronics are two of the leading sensor-manufactures of China who are providing a wide range of gas detecting sensors that are locally available in Bangladesh and yet has not been applied to methane content measurement in biogas operations. In This paper we are reporting on the application of a purpose-built propane, butane detector for methane gas detection within the range of accuracy for it to be applied in methane detection in a biogas stream. This paper, reports on application and calibration of the methane detecting sensor MQ-4 with promising result. Based on the study we postulate that the sensor can be used to detect methane for an on-line monitoring of many environmental, industrial purposes such as bio digesters, integrated waste management facility. The cost of fabrication of the sensor system is only $18 making it a viable sensor with respect to cost for application in Bangladesh.

Improving Air Pollutant Metal Oxide Sensor Quantification Practices through: An Exploration of Sensor Signal Normalization, Multi-Sensor and Universal Calibration Model Generation, and Physical Factors Such as Co-Location Duration and Sensor Age

As low-cost sensors have become ubiquitous in air quality measurements, there is a need for more efficient calibration and quantification practices. Here, we deploy stationary low-cost monitors in Colorado and Southern California near oil and gas facilities, focusing our analysis on methane and ozone concentration measurement using metal oxide sensors. In comparing different sensor signal normalization techniques, we propose a z-scoring standardization approach to normalize all sensor signals, making our calibration results more easily transferable among sensor packages. We also attempt several different physical co-location schemes, and explore several calibration models in which only one sensor system needs to be co-located with a reference instrument, and can be used to calibrate the rest of the fleet of sensor systems. This approach greatly reduces the time and effort involved in field normalization without compromising goodness of fit of the calibration model to a significant extent. We also explore other factors affecting the performance of the sensor system quantification method, including the use of different reference instruments, duration of co-location, time averaging, transferability between different physical environments, and the age of metal oxide sensors. Our focus on methane and stationary monitors, in addition to the z-scoring standardization approach, has broad applications in low-cost sensor calibration and utility.

Fourier transform infrared spectroscopy and interference of volatile organic compounds on measurements of methane (CH4) fluxes at tree stems – a general phenomenon for plant systems?

Fourier transform infrared spectroscopy and interference of volatile organic compounds on measurements of methane (CH₄) fluxes at tree stems – a general phenomenon for plant systems?

Towards a new transfer standard for speed of sound measurements in liquids at cryogenic temperatures

Traceability of fluid flow measurement is a prerequisite for the accurate determination of transferred mass, heat and energy. However, considering the wide range of flow-rates, temperature, pressure, viscosity and densities, which is of interest for practical applications of fluid flow metrology, the accurate calibration of ultrasonic flow meters still represents a demanding task. Alternative to the usual gravimetric calibration, the possibility to provide traceability through using a speed of sound standard has been less explored. In this work, we describe and discuss the performance of an ultrasonic cell, and the feasibility of using this sensor to provide traceable measurements of the speed of sound. The instrument has been designed to serve as transfer standard for speed of sound and, its features make it suitable for the calibration of ultrasonic flowmeters both in the laboratory and on industrial pipelines. The sensor has been tested by performing speed of sound measurements in liquid methane between 100 K and 162 K and for pressure up to 10 MPa. The expanded relative uncertainty (k=2) of the speed of sound w is Ur(w)=0.15% for temperature below 130 K and Ur(w)=0.32% above 130 K. The obtained results are found in agreement with previously published measurements and with the predictions of the Setzmann and Wagner and GERG equations of state. Along with the results of speed of sound measurements and their expanded (k=2) uncertainty, we provide a detailed discussion of the procedures adopted to improve the stability of the sensor, and the specific corrections applied considering the cryogenic working conditions.

A sensitive methane sensor of a ppt detection level using a mid-infrared interband cascade laser and a long-path multipass cell

An ultra-high sensitivity sensor combining a mid-IR (MIR) interband cascade laser (ICL) at center wavelength of 3.37 μm and a multi-pass cell (MPC) with a path-length of 580 m was designed and implemented for methane detection. The ultra-high sensitivity is achieved due to the higher absorbance in the MIR than in the near infrared (NIR), a long interaction path length, and the implementation of a wavelet denoising processing algorithm. The performance of the sensor was evaluated with direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) in a series of measurements. For the sensor working in the DAS measurement mode, the optimal set of sub-wavelet functions was chosen and utilized for denoising. A calibration gas with methane concentration of 2.0 ppm was measured with a relative error of ± 1%. The minimum of the Allan deviation of the sensor of 3 ppb was achieved with an averaging time of 200 s. For the WMS technique with the Allan deviation analysis the sensor detection limit for methane of 560 ppt with 290 s averaging time was determined, which is a significant improvement compared to our DAS results and previous reports. The developed sensor has broad applicability in the high-sensitivity measurements of methane and other trace gases.

Assessment of the accuracy of open-circuit respiration chambers for measuring enteric methane emissions in cattle

Ruminants are the main source of methane emissions from the agricultural sector. Emission inventories and mitigation strategies require reliable technics of measurement. The respiration chamber methodology is a precise approach for measuring enteric methane emissions in cattle. A set of experiments was carried out to validate two respiration chambers for measuring enteric methane emissions of cattle. The chambers were calibrated considering three main components: the methane analyzer, the air duct and air extraction system, and the chamber itself, by evaluating linearity and response time of the analyzer, plateau variability and high purity methane recoveries in chambers. Recovery test calculations carried out after releasing high purity methane into the chambers gave calibration factors of 0.95 ± 0.05 and 1.03 ± 0.03 for the complete system of respirations chambers one and two, respectively, with corresponding uncertainties of 4.87 and 2.49%. Thus, the respiration chambers for enteric methane measurements of cattle at the University of Yucatan, Mexico function with precision and accuracy. This technique can be used to establish methane inventories and methane mitigation strategies in cattle.

A focused review on membrane contactors for the recovery of dissolved methane from anaerobic membrane bioreactor (AnMBR) effluents

The need for a more sustainable wastewater treatment is more relevant now due to climate change. Production and reuse of methane from anaerobic treatment is one pathway. However, this is defeated by the presence of dissolved methane in the effluent and would be released to the environment, adding to the greenhouse gas emissions. This review paper provided summary and analysis of studies involved in the production of dissolved methane from AnMBR, focusing with actual methane measurement (gas and dissolved) from AnMBR with different types of wastewater. Then more focused discussion and analysis on the use of membrane-based technology or membrane contactors in the recovery of dissolved methane from AnMBR effluent are included, with its development and energy analysis. The dissolved methane removal and recovery rate of membrane contactors can be as high as 96% and 0.05 mol methane/m2/h, respectively, with very low additional energy requirement of 0.01 kWh/m3 for the recovery. Future perspectives presented focus on the long-term evaluation and modelling of membrane contactors and on the membrane modifications to improve the selectivity of membranes to methane and to limit their fouling and wetting, thus making the technology more economical for resource recovery.

Isotopic gas analysis by means of mid-infrared photoacoustic spectroscopy targeting human exhaled air.

There is a great need for cost-efficient non-invasive medical diagnostic tools for analyzing humanly exhaled air. Compared to present day methods, photoacoustic spectroscopy (PAS) can provide a compact and portable (bedside), sensitive and inexpensive solution. We demonstrate a novel portable photoacoustic spectroscopic platform for isotopic measurements of methane (CH4). We identify and discriminate the 12CH4- and 13CH4 isotopologues and determine their mixing ratio. An Allan deviation analysis shows that the noise equivalent concentration for CH4 is 200 ppt (pmol/mol) at 100 s of integration time, corresponding to a normalized noise equivalent absorption coefficient of 5.1×10-9Wcm-1Hz-1/2, potentially making the PAS sensor a truly disruptive instrument for bedside monitoring using isotope tracers by providing real-time metabolism data to clinical personnel.

Blinded evaluation of airborne methane source detection using Bridger Photonics LiDAR

Controlled, fully-blinded methane releases and ancillary on-site wind measurements were performed during a separate airborne survey of active oil and gas facilities to quantitatively evaluate the capabilities and potential utility of the Bridger Photonics LiDAR-based airborne Gas Mapping LiDAR™ (GML) methane measurement technology under realistic field conditions. Importantly, although Bridger Photonics knew there was a ground team working in the area to deploy wind sensors as part of the broader survey of facilities, they had no knowledge whatsoever that controlled releases were taking place and were not informed of this until all data processing was complete. Thus, the presented data allow a true, fully-blinded assessment of the airborne technology's ability to both detect and locate unknown methane sources within active oil and gas facilities, as well as to quantify their release rates. Results were used to derive a lower-sensitivity limit threshold as a function of wind speed, which matches well with the broader field survey results. Comparison of measurement results with and without the benefit of on-site wind data reveal that uncertainty in the GML source quantification is a direct linear function of the uncertainty in the wind speed. Quantification uncertainties (1σ) of ±31–68% can be expected for sources near the sensitivity limit. The derived sensitivity limit function was incorporated into exploratory simulations using the Fugitive Emissions Abatement Simulation Toolkit (FEAST), which suggest that the Bridger GML technology has comparable performance to optical gas imaging (OGI) camera surveys both in terms of fraction of total emissions detected and anticipated net mitigation. The relative performance of the Bridger GML technology would be expected to improve or worsen as the assumed underlying distribution of source magnitudes becomes more or less positively skewed (i.e. more or less dominated by larger sources such as tank vents). Overall, the Bridger GML technology is shown to be capable of detecting, locating, and quantifying individual sources at or below the magnitudes of recent regulated venting limits. The presented detection sensitivity function will be useful for modelling potential alternate leak detection and repair strategies and interpreting future airborne measurement data.

A novel gas sensing scheme using near-infrared multi-input multi-output off-axis integrated cavity output spectroscopy (MIMO-OA-ICOS)

We demonstrated a novel multi-input multi-output (MIMO) laser-to-cavity coupling scheme in off-axis integrated cavity output spectroscopy (OA-ICOS) for cavity mode noise suppression. Theoretical investigation was performed to explore the relation between the number of splitting beams and the MIMO parameters. Mode distribution and propagation inside the cavity was simulated. The noise suppression factor of the MIMO scheme and the noise level and dominated noise in the cavity were studied based on cavity mode simulation. Methane measurements were carried out using a dual-input dual-output (DIDO, N = 2) sensor system to validate the presented scheme, and good agreement was found between simulation and experiment.

Off-axis integrated cavity output spectroscopy for real-time methane measurements with an integrated wavelength-tunable light source

Off-axis integrated cavity output spectroscopy (OA-ICOS) is a sensitive technique for trace gas sensing. A wavelength modulated off-axis integrated cavity output spectroscopy (WM-OA-ICOS) based CH4 detection system was presented in this paper. An integrated near-infrared (NIR) light source consisting of a digital temperature controller, a current modulator and a 1.65 μm distributed feedback (DFB) laser was developed. A 50.8 mm long assembly Fabry–Perot (F-P) cavity was designed and used as the gas chamber. Wavelength modulation spectroscopy (WMS) was employed to improve the signal to noise ratio (SNR) of the system and a LabVIEW-based orthogonal lock-in amplifier was developed to extract the second harmonic (2f) signal. The experimental values of the optimum modulation parameters were determined and CH4 measurements were carried out to demonstrate the effectiveness and sensitivity of the sensor system. A quantitative characterization of long-term stability and detection sensitivity is presented. Based on Allan variance analysis, the limit of detection is 10.5 ppm when the averaging time is 30 s which can be improved easily by changing the cavity lens with higher reflectivity or increase the distance between the cavity mirrors. The sensor system was insensitive to optical alignment and can be easily serviced on site. Furthermore, this system can be further integrated by using self-developed lock-in amplifier based on our previous work, which enables the system to have good prospects in industrial field.

Performance of open-path GasFinder3 devices for CH<sub>4</sub> concentration measurements close to ambient levels

Abstract. Open-path measurements of methane (CH4) with the use of GasFinder systems (Boreal Laser Inc, Edmonton Canada) have been frequently used for emission estimation with the inverse dispersion method (IDM), particularly from agricultural sources. It is common to many IDM applications that the concentration enhancement related to CH4 sources is small, typically between 0.05 and 0.5 ppm, and accurate measurements of CH4 concentrations are needed at concentrations close to ambient levels. The GasFinder3-OP (GF3) device for open-path CH4 measurements is the latest version of the commercial GasFinder systems by Boreal Laser Inc. We investigated the uncertainty of six GF3 devices from side-by-side intercomparison measurements and comparisons to a closed-path quantum cascade laser device. The comparisons were made at near-ambient levels of CH4 (85 % of measurements below 2.5 ppm) with occasional phases of elevated concentrations (max. 8.3 ppm). Relative biases as high as 8.3 % were found, and a precision for half-hourly data between 2.1 and 10.6 ppm-m (half width of the 95 % confidence interval) was estimated. These results deviate from the respective manufacturer specifications of 2 % and 0.5 ppm-m. Intercalibration of the GF3 devices by linear regression to remove measurement bias was shown to be of limited value due to drifts and step changes in the recorded GF3 concentrations.

Experimental Evaluation of Volatile Organic Compound Quantification Methods for Reciprocating Natural Gas Engines

Abstract Compressor stations utilizing large-bore natural gas engines transport natural gas through pipelines worldwide. One emission class regulated by the Environmental Protection Agency (EPA) is volatile organic compounds (VOCs), which are nonmethane, nonethane, nonaldehyde hydrocarbons. The combination of a gas chromatograph (GC) and a flame ionization detector (FID) can measure VOCs, following EPA Method 18/25A. The Fourier transform infrared spectrometer (FTIR) also measures VOCs, following EPA Method 320. Multiple VOC calculation techniques are utilized, some combining measurements from separate analyzers. Two basic methods of extracting exhaust gas are direct extraction and Tedlar bag sampling. In this study, various VOC quantification methods are evaluated. Exhaust gas was sampled from a Cooper-Bessemer GMV lean-burn engine and a Caterpillar G3304 rich-burn engine. The GMV was tested in three configurations: open chamber spark ignition, precombustion chamber (PCC) ignition, and PCC ignition with high-pressure fuel injection. Ignition timing sweeps were performed on both engines, and a fuel variability test was performed on the GMV. Results showed that the Gasmet and MKS FTIRs’ (Method 320) VOC measurements deviate significantly from the HP GC when measuring low molar concentrations, albeit below regulatory limits. A common VOC quantification approach is subtracting the sum of methane and ethane FTIR measurements from a total hydrocarbon measurement utilizing a FID. This method produces uncertainties of 190% and overestimates VOC concentration by an average of 100%. The Tedlar bag sampling method produced VOC measurements within −2% of the direct extraction method.

Comparison of laser-based photoacoustic and optical detection of methane

Abstract. The measurement of low methane (CH4) concentrations is a key objective for safety of industrial and public infrastructures and in environmental research. Laser spectroscopy is best suited for this purpose because it offers high sensitivity, selectivity, dynamic range, and a fast measurement rate. The physical basis of this technique is infrared absorption of molecular gases. Two detection schemes – direct absorption spectroscopy (DAS) and photoacoustic spectroscopy (PAS) – are compared at three wavelength regions in the near-infrared (NIR), mid-wavelength (MWIR), and long-wavelength (LWIR) infrared ranges. For each spectral range a suitable semiconductor laser is selected and used for both detection techniques: a diode laser (DL), an interband cascade laser (ICL), and a quantum cascade laser (QCL) for NIR, MWIR and LWIR, respectively. For DAS short absorption path lengths comparable to the cell dimensions of the photoacoustic cell for PAS are employed. We show that for DAS the lowest detection limit can be achieved in the MWIR range with noise-equivalent concentrations (NECs) below 10 ppb. Using PAS, lower detection limits and higher system stabilities can be reached compared to DAS, especially for long integration times. The lowest detection limit for PAS is obtained in the LWIR with a NEC of 7 ppb. The different DAS and PAS configurations are discussed with respect to potential applications.

Relative flux measurements of biogenic and natural gas-derived methane for seven U.S. cities

Using the Purdue University Airborne Laboratory for Atmospheric Research, we measured concentrations of methane and ethane emanating from seven U.S. cities (New York, NY, Philadelphia, PA, Washington, D.C./Baltimore, MD, Boston, MA, Chicago, IL, Richmond, VA, and Indianapolis, IN), in order to determine (with a median 95% CI of roughly 7%) the fraction of methane emissions attributable to natural gas (Thermogenic Methane Emission Ratio [TMER]), for both summer and winter months. New methodology is introduced to compute inflow concentrations and to accurately define the spatial domain of the sampling region, using upwind measurements coupled with Lagrangian trajectory modeling. We show discrepancies in inventory-estimated TMER from cities when the sample domain is defined using political boundaries versus urban centers encircled by the flight track and highlight this as a potential source of error common to top-down studies. We found that methane emissions of natural gas were greater than winter biogenic emissions for all cities except Richmond, where multiple landfills dominate. Biogenic emissions increased in summer, but natural gas remained important or dominant (20%–80%). National inventories should be updated to reflect the dominance of natural gas emissions for urban environments and to account for seasonal increases in biogenic methane in summer.