Measurements Of Methane Concentrations Research Articles

Calibration and field deployment of low-cost sensor network to monitor underground pipeline leakage

Recent technological advances in methane detection have improved leak detection and repair. However, current methods to reliably measure methane concentrations rely on expensive instruments or demand significant labor input. There is interest in using affordable methane sensors that are responsive to ppmv level changes in methane concentrations in both urban and rural environments for monitoring underground natural gas pipeline leaks. This is especially relevant for situations where potentially significant leaks cannot be repaired immediately or smaller leaks that require long-term monitoring and further evaluation. In this work, a low-cost sensor unit, equipped with a metal oxide sensor, was designed, built, and calibrated over a wide range of methane concentrations and environmental conditions in preparation for field application. A network of these sensors was then installed at the test site and used to measure methane concentrations at ground level above known sub-surface natural gas emissions which emulated underground gas pipeline leaks. This low-cost sensor network measured over 4 days total for the two different known leakage rates. Results demonstrate that the sensors can continuously measure relative methane variability for extended periods but require calibration for a wide range of temperature and humidity conditions to properly determine absolute gas (i.e., methane) concentrations. When a regression analysis was conducted to evaluate the effects of meteorological parameters on methane concentration, air temperature and wind speed have strong impacts on the concentration. Overall, the network approach allows improved identification of leak location and monitoring of underground natural gas leaks.

A Portable Device for Methane Measurement Using a Low-Cost Semiconductor Sensor: Development, Calibration and Environmental Applications.

Methane is a major greenhouse gas and a precursor of tropospheric ozone, and most of its sources are linked to anthropogenic activities. The sources of methane are well known and its monitoring generally involves the use of expensive gas analyzers with high operating costs. Many studies have investigated the use of low-cost gas sensors as an alternative for measuring methane concentrations; however, it is still an area that needs further development to ensure reliable measurements. In this work a low-cost platform for measuring methane within a low concentration range was developed and used in two distinct environments to continuously assess and improve its performance. The methane sensor was the Figaro TGS2600, a metal oxide semiconductor (MOS) based on tin dioxide (SnO2). In a first stage, the monitoring platform was applied in a small ruminant barn after undergoing a multi-point calibration. In a second stage, the system was used in a wastewater treatment plant together with a multi-gas analyzer (Gasera One Pulse). The calibration of low-cost sensor was based on the relation of the readings of the two devices. Temperature and relative humidity were also measured to perform corrections to minimize the effects of these variables on the sensor signal and an active ventilation system was used to improve the performance of the sensor. The system proved to be able to measure low methane concentrations following reliable spatial and temporal patterns in both places. A very similar behavior between both measuring systems was also well noticeable at WWTP. In general, the low-cost system presented good performance under several environmental conditions, showing itself to be a good alternative, at least as a screening monitoring system.

Investigations of dynamic properties of an integrated methane and rock outburst sensor

Outbursts of methane and rocks are, similarly to rock bursts, the biggest hazards in deep mines and are equally difficult to predict. The violent process of the outburst itself, along with the scale and range of hazards following the rapid discharge of gas and rocks, require solutions which enable quick and unambiguous detection of the hazard.The paper presents the functions of an integrated outburst detector which was equipped with three measuring and detection elements: a pressure sensor, a microphone and a chamber for constant measurement of methane concentration. A measuring stand for testing the dynamic properties of the integrated methane discharge sensor is described. It has been shown that both the pressure transducer and the microphone react immediately after a change in thermodynamic conditions, and the time constant of the pellistor methane concentration sensor was estimated at a few seconds. Field tests of the integrated sensor were also carried out, the main purpose of which was to verify the dynamic parameters of the sensor in medium scale experimental conditions during methane and coal dust explosions in the testing gallery at an experimental mine.

Измерения фоновой концентрации метана дистанционным лидаром на километровых трассах в районе Московской области.

Local path measurements of the background methane concentration in the northeast of the Moscow Region were carried out using a remote active lidar based on a powerful Raman amplifier of optical radiation in the wavelength range of ~ 1650 nm. The radiation power in the pulse was about 3 W. The trasses were selected taking into account possible anomalous deviations of the background of atmospheric methane and included forests, gasified buildings with natural gas, a peat lake, a road with heavy traffic, a livestock farm and a solid waste landfill. The length of the distances ranged from ~ 0.6 km to ~ 3.15 km. The highest background concentration of methane was observed over a livestock farm, over a highway and a solid waste landfill, which confirms the fact of an increase in gas emissions over these facilities. Also higher methane levels were observed above of the gasified homes and the heavy traffic road, indicating a possible increase in the number of vehicles using methane as fuel and a possible leak of natural gas from pipelines supplying buildings with natural gas.

Двухполяризационное усиление оптического излучения на эффекте Рамана для передатчика лидара.

A comparison is made of the spectral distortions of the output radiation of a Raman amplifier in the case of one and two-polarization amplification of modulated radiation in an extended optical fiber. With an output power of 3.5 W at a wavelength of 1649 nm, the spectral distortions for bipolarization amplification are lower, which makes it possible to increase the amplifier output power to ~ 4 W, and the level of spectral distortions at the amplifier output makes possible to carry out lidar measurements of methane concentration by a remote method with high accuracy. Simulation of bipolarization Raman amplification was carried out along with experimental verification. For this simulation, the coefficient of depolarization of radiation propagating in an extended single-mode fiber was introduced. The experimental results and the results of theoretical modeling are in good agreement. An increase in the amplifier power also makes it possible to increase the methane sensing range in an open atmosphere with lidars using Raman amplifiers as transmitters.

Volumetric Mapping of Methane Concentrations at the Bush Hill Hydrocarbon Seep, Gulf of Mexico

The role of methane as a green-house gas is widely recognized and has sparked considerable efforts to quantify the contribution from natural methane sources including submarine seeps. A variety of techniques and approaches have been directed at quantifying methane fluxes from seeps from just below the sediment water interface all the way to the ocean atmosphere interface. However, there have been no systematic efforts to characterize the amount and distribution of dissolved methane around seeps. This is critical to understanding the fate of methane released from seeps and its role in the submarine environment. Here we summarize the findings of two field studies of the Bush Hill mud volcano (540 m water depth) located in the Gulf of Mexico. The studies were carried out using buoyancy driven gliders equipped with methane sensors for near real time in situ detection. One glider was equipped with an Acoustic Doppler Current Profiler (ADCP) for simultaneous measurement of currents and methane concentrations. Elevated methane concentrations in the water column were measured as far away as 2 km from the seep source and to a height of about 100 m above the seep. Maximum observed concentrations were ∼400 nM near the seep source and decreased away steadily in all directions from the source. Weak and variable currents result in nearly radially symmetric dispersal of methane from the source. The persistent presence of significant methane concentrations in the water column points to a persistent methane seepage at the seafloor, that has implications for helping stabilize exposed methane hydrates. Elevated methane concentrations in the water column, at considerable distances away from seeps potentially support a much larger methane-promoted biological system than is widely appreciated.

Discrete Sample Introduction Module for Quantitative and Isotopic Analysis of Methane and Other Gases by Cavity Ring-Down Spectroscopy

Carbon dioxide (CO2) and methane (CH4) are natural and anthropogenic products that play a central role in the global carbon cycle and regulating Earth's climate. Applications utilizing laser absorption spectroscopy, which continuously measure concentrations and stable isotope ratios of these greenhouse gases, are routinely employed to measure the source and magnitude of atmospheric inputs. We developed a discrete sample introduction module (DSIM) to enable measurements of methane and CO2 concentrations and δ13C values from limited volume (5-100 mL) gas samples when interfaced with a commercially available cavity ring-down spectroscopy (CRDS) analyzer. The analysis has a dynamic range that spans six orders of magnitude from 100% analyte to the lower limit of instrument detection (2 ppm). We demonstrate system performance for methane by comparing concentrations and δ13C results from the DSIM-CRDS system and traditional methods for a variety of sample types, including low concentration (nanomolar CH4) seawater and high concentration (>90% CH4) natural gas. The expansive concentration range of the field-portable DSIM-CRDS system can measure enhances analytical performance for investigating methane and CO2 dynamics and, potentially, other gases measured by laser absorption spectroscopy.

Methane photo-acoustic gas analyzer based on 7.7-μm quantum cascade laser

The photo-acoustic (PA) methane gas analyzer based on a quantum cascade laser (QCL; ~7.7 μm/1800 Hz/24 mW), a resonant differential PA detector, and a sealed gas-filled cell was investigated. The measurement of methane concentration below the background value in the air (~0.3 ppm CH4) is shown, the standard dispersion was (1σ) ≈ (10–11) ppb CH4 with an integration time of 10 s. Under conditions of temperature instability (or emission wavelength) of QCL when normalized to a gas-filled cell, the relative measurement error of the CH4 concentration does not exceed 3%. A decrease in the average QCL radiation power (~24–12–6 mW) leads to a noticeable deterioration in the threshold sensitivity of the PA gas analyzer. It is recommended to increase the average QCL power level to ~50 mW. The dynamic range of measuring the concentration of methane of the PA gas analyzer in the linear mode was ~4 decades (from 0.3 ppm to 2000–3000 ppm CH4).

Simulation of methane concentration measurements by lidar in a cloudy atmosphere

Simulation of the vertical profile of methane concentration in the Earth’s atmosphere is simulated in the absence of direct visibility on the spacecraft (SC)-Earth surface route. At high latitudes, clouds cover the Earth’s surface for a significant time, so it is important to use all possibilities so that there are no significant windows of uncertainty in data acquisition along the entire path, including the lower troposphere. For modeling purposes the vertical profile of methane concentration was approximated by a sixth-degree polynomial, and the profile was refined by varying its coefficients until is coincide with the experimental data. The proposed method of using the reflected and scattered signal from clouds and cloud formations and extrapolating data along the vertical profile of methane to the entire path in the absence of direct visibility of the Earth’s surface ensures uninterrupted data acquisition, thereby increasing the accuracy and reliability of statistical materials for determining the methane concentration, and, consequently, its influence on the dynamics of the climate in general.

Methane cycling within sea ice: results from drifting ice during late spring, north of Svalbard

Abstract. Summer sea ice cover in the Arctic Ocean has declined sharply during the last decades, leading to changes in ice structures. The shift from thicker multi-year ice to thinner first-year ice changes the methane storage transported by sea ice into remote areas far away from its origin. As significant amounts of methane are stored in sea ice, minimal changes in the ice structure may have a strong impact on the fate of methane when ice melts. Hence, sea ice type is an important indicator of modifications to methane pathways. Based on measurements of methane concentration and its isotopic composition on a drifting ice floe, we report on different storage capacities of methane within first-year ice and ridged/rafted ice, as well as methane supersaturation in the seawater. During this early melt season, we show that ice type and/or structure determines the fate of methane and that methane released into seawater is a predominant pathway. We suggest that sea ice loaded with methane acts as a source of methane for polar surface waters during late spring.

Simultaneous Measurements of Refractive Index and Methane Concentration through Electromagnetic Fano Resonance Coupling in All-Dielectric Metasurface.

Dual-parameter measurements of refractive index and methane concentration based on electromagnetic Fano resonance are proposed. Two independent Fano resonances can be produced through electric dipole and toroidal dipole resonance in an all-dielectric metasurface separately. The linear relationship between the spectral peak-shifts and the parameters to be measured will be obtained directly. The refractive index (RI) sensitivity and gas sensitivity are 1305.6 nm/refractive index unit (RIU), −0.295 nm/% for one resonance peak (dip1), and 456.6 nm/RIU, −0.61 nm/% for another resonance peak (dip2). Such a metasurface has simpler structure and higher sensitivity, which is beneficial for environmental gas monitoring or multi-parameter measurements.

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?

The Balance of Methane and Ventilation as a Tool for Methane Hazard Assessment in the Areas of Longwalls Exploited in Hard Coal Mines

ABSTRACT Purpose This article presents an algorithm for the current assessment of methane hazards during the exploitation of longwalls in conditions where there are methane hazards. The algorithm has been developed within the framework of the international AVENTO project (Advanced Tools For Ventilation and Methane Emissions Control), carried out in Poland, inter alia, by the Central Mining Institute in cooperation with Kompania Weglowa SA (KW SA).The algorithm was developed based on the analysis of the ventilation-methane balances for longwall areas, based on the data registered by automatic methane sensors and the velocity of ventilating air. Methods Multiple research methods were used, such as: observation, a questionnaire and statistical methods.The questionnaire was used for the preliminary determination of methane hazards in the longwalls belonging to the industrial partner (KW SA). The polls were used to obtain relevant information about the hazards and means of prevention taken, such as: the methane content in the seam, the emissions of methane into the exploitation workings, the volume of methane drainage, the ventilation system used, and the amount of ventilation air used to combat the methane hazard. Based on the poll's data, the longwalls with methane emissions in their environment were selected for testing, based on long-term observations of changes in the concentrations of methane in the ventilation air and in the methane drainage net. Methane concentration measurements were based on the values recorded by the methane sensors located in the workings which were considered to be most dangerous. For data processing a statistical method was used. In the research, the average results of the indicated concentrations of methane from the methane sensors were used for the correlation between the average values of methane emission in the region of the longwall or methane drainage, with other parameters, such as absolute pressure changes on the surface, technological processes or cycles in the longwall. For the evaluation of the methane hazard, an indicator was proposed, these being the ratio of the ventilation methane bearing capacity to the criterial methane bearing capacity. An increase of this indicator indicates an increase in the level of methane hazard. Results On the basis of the average daily value of the methane hazard status indicator, an algorithm for the assessment and visualization of methane hazard in the areas of the active longwalls was developed. The algorithm contains a list of technical and organizational actions which should be taken in the event of unfavourable risk assessment of methane hazard, reflecting very high risk or unsafe conditions for conducting further work. Practical implications The proposed algorithm can be used for the ongoing assessment of methane hazard in areas of exploited longwalls in order to support staff in surface control rooms and in ventilation departments. Originality/value The current assessment of methane hazard in the areas of longwalls which are under methane conditions by means of the developed algorithm will improve the safety of exploitation.

Greenhouse gases (CO2 and CH4) at an urban background site in Athens, Greece: Levels, sources and impact of atmospheric circulation

Year-round carbon dioxide (CO2) and methane (CH4) concentration measurements, performed for the first time in the city of Athens, Greece from December 21, 2018 to December 31, 2019, are presented in this study and analyzed in relation to atmospheric circulation patterns at a local, regional and long-range transport scale. Clear diurnal and seasonal variations of both greenhouse gases were detected. The observed increased levels during night and early morning hours are attributed to traffic/heating emissions and leakages of residential natural gas for CO2 and CH4, respectively. Using CO2 and CH4 levels simultaneously measured at the regional background site at Finokalia (Greece), increments in their levels due to local and regional anthropogenic sources within the city were assessed. For CO2, maximum and minimum increments were clearly observed during winter and summer respectively, suggesting a greater impact of combustion of fossil fuel and especially of biomass on CO2 levels during winter. On the other hand, CH4 increments were similar in all seasons, suggesting that local sources of CH4 remain quite constant year-round. Through the implementation of the Conditional Probability Function (CPF), the emission sources of theses greenhouse gases have been localized to the northern and the eastern domains of the Athens basin. Stagnant atmospheric conditions were also associated with an increased likelihood of CO2 and CH4 episodes. Backward modeling simulations with FLEXPART and HYSPLIT models indicate an industrial zone and a petrochemical zone, situated to the north and to the west of Athens respectively, as possible CH4 regional sources as well as possible CO2 contributions from southern directions attributed to shipping emissions from the port of Piraeus. The present study provides knowledge needed for the determination of greenhouse gas emission mitigation strategies in Athens.

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.

Fibre-coupled, multiplexed methane detection using range-resolved interferometry

We describe the first use of range-resolved interferometric signal processing for measurement of spectral transmission. This was applied to gas sensing using tunable diode laser spectroscopy, allowing the simultaneous and independent measurement of methane concentrations in multiple gas cells. The system uses a single injection-current modulated diode laser and a single photodetector. For three gas cells, we show the ability of the system to measure methane at noise equivalent concentrations of less than 200 ppm for a 0.5 s measurement period and a potential noise equivalent concentration (1σ) of <20 ppm with 150 s averaging time. We further show that cross-talk between cells is below the experimental uncertainty for the system.

Sensitivity Enhancement of Methane Detection Based On Hollow Core Photonic Crystal Fiber

Monitoring methane (CH4) concentration is essential in many industrial and environmental applications. Emission of such gases is indeed important to detect for health, safety and environmental reasons. The major risk in all these areas is an explosion hazard, which may occur if methane reaches its Lower Explosive Limit (LEL) of5% concentration in air. For that reason, it is necessary to develop gas sensors to monitor that methane levels below this value. Due to a weak absorption of methane, this gas is difficult to detect using conventional methods.Hollow core photonic crystal fibers (HC-PBF) have emerged as a promising technology in the field of gas sensing. The strong interaction achievable with these fibers are especially advantageous for the detection of weakly absorbing regions of methane. In this paper, we investigated, by full vectorial finite element method (FV-FEM) in Rsoft CAD environment, the dependency of relative sensitivity on the fiber parameters and wavelength. Consequently, we introduced the optimal structureof an index guiding hollow core photonic crystal fiber capable of measuring methane concentrations down to 0.1%in air. The simulations showed that the sensing sensitivity increased with an increase in the core diameter and a decrease in the distance between centers of two adjacent holes.

Распределение потоков метана на границе вода–атмосфера в различных районах Мирового океана

For the first time, methane fluxes at the water-atmosphere interface were calculated for the water area of Pacific, Indian, and Atlantic oceans (for the area about 30,000 miles) on the basis of the expeditionary measurements of methane concentrations in the surface layer of water and subsurface layer of the atmosphere along the entire course of the vessel. Methane fluxes at the water-atmosphere interface were calculated for the water areas of the Pacific, Indian and Atlantic oceans. In the result of the studies carried out in various regions of the World Ocean, an uneven spatial distribution of methane fluxes from strong absorption to emission of anomalous intensity was observed. The article presents the results of a detailed study for the deepwater area of the Indian Ocean open waters in the northern part of the Ninetyeast Ridge. Both supersaturation and undersaturation of seawater respectively to its concentrations in the atmosphere have been revealed on the basis of the direct measurements of methane concentrations in the ocean surface water layer. The distribution of dissolved methane in the water column of the Indian Ocean has been considered.

Mobile autonomous methane monitoring stations for emission measurement

Natural gas has been forecast to continue grow up to 30% for the next 40 years and will remain as a key energy source. Alongside this projected growth, both the government and the industry have committed to reduce emission reductions. A critical focus is fugitive emissions, which are related to leaks or unintended losses of methane from sources such as hydrocarbon production, processing, transport, storage, transmission and distribution. The need for measuring and monitoring these emissions has been recognised in significant environmental inquiries related to the gas industry, such as the Northern Territory Fracking Inquiry (Pepper et al. 2018) and required in section D of the NT Code of Practice. This study describes an autonomous emission monitoring station developed to address the challenge of characterising temporally varying fugitive methane emissions. It has been designed specifically to tolerate the Australian outback’s extreme climateswhile providing laboratory-grade measurements in real-time at locations where there will be no access to grid power and standard telecommunications. Preliminary results demonstrating the continuous real-time measurements of methane and ethane concentrations of temporally varying phenomena will be presented. Specifically, the detection of methane and ethane concentrations and temporal changes related to bushfire progress will be shown.