Ppm For CH4 Research Articles

Photoacoustic methane gas analyser based on a 3.3-μm optical parametric oscillator

We demonstrate a bench-scale prototype of a photoacoustic (PA) methane gas analyser that takes advantage of an optical parametric oscillator (OPO) based on a fan-out MgO : PPLN structure and resonant differential PA detector. The OPO emits in a repetitively pulsed mode (∼1750 Hz) at an idler wavelength of ∼3.3 μm with an average power of ∼40 – 50 mW. Using the prototype laser PA gas analyser, we experimentally demonstrate the feasibility of measuring the background methane concentration in air (∼2 – 3 ppm of CH4). The threshold sensitivity of the PA gas analyser (1σ) is determined to be ∼ 49 ppb of CH4.

A dual-gas sensor for simultaneous detection of methane and acetylene based on time-sharing scanning assisted wavelength modulation spectroscopy.

Methane (CH4) and acetylene (C2H2) are important bioscience and chemical gases. The real-time monitoring and analysis of them have important research value in industrial process control. The time-sharing scanning assisted wavelength modulation spectroscopy (WMS) technique is developed for real-time and simultaneous detection of CH4 and C2H2. This system involves two near-infrared distributed feedback (DFB) lasers and a compact multipass cavity with an effective optical path of 52.2m. The selected strong absorption lines of methane and acetylene are located at 6046.96cm-1 and 6531.7cm-1, respectively. The experiment environment is conducted at room temperature 23°C and pressure 760Torr. The sensor performance, including the minimum detection limit (MDL) and the stability, was improved by eliminating the influence of light intensity fluctuation using the WMS-2f/SAW technique. Allan deviation analysis indicates that a MDL of 0.1ppm for CH4 and 0.2ppm for C2H2 are achieved with 1-s integration time. And the instrument response time is about 44s through the continuous analysis of standard gases. This sensitive, simple, reliable, and lowcost dual-gas sensor is very suitable for applications in the field environment, chemical process, and many other gas-phase analysis areas.

A portable miniaturized laser heterodyne radiometer (mini‑LHR) for remote measurements of column CH4 and CO2.

We present the design of a portable version of our miniaturized laser heterodyne radiometer (mini-LHR) that simultaneously measures methane (CH4) and carbon dioxide (CO2) in the atmospheric column. The mini-LHR fits on a backpack frame, operates autonomously, and requires no infrastructure because it is powered by batteries charged by a folding 30 W solar panel. Similar to our earlier instruments, the mini-LHR is a passive laser heterodyne radiometer that operates by collecting sunlight that has undergone absorption by CH4 and CO2. Within the mini-LHR, sunlight is mixed with light from a distributive feedback (DFB) laser centered at approximately 1.64 μm where both gases have absorption features. The laser scans across these absorption features roughly every minute and the resulting beat signal is collected in the radio frequency (RF). Scans are averaged into half hour and hour data products and analyzed using the Planetary Spectrum Generator (PSG) retrieval to extract column mole fractions. Instrument performance is demonstrated through two deployments at significantly different sites in interior Alaska and Hawaii. The resolving power (λ/∆λ) is greater than 500,000 at 1.64 μm with precisions of better than 20 ppb and 1 ppm for CH4 and CO2, respectively. Because mini-LHR instruments are portable and can be co-located, they can be used to characterize bias between larger, stationary, column observing instruments. In addition, mini-LHRs can be deployed quickly to respond to transient events such as methane leaks or can be used for field studies targeting geographical regions.

Influence of air parcel trajectories on CO2 and CH4 concentrations in the northern plateau of the Iberian Peninsula

This study presents a simpler procedure for grouping air parcel back trajectories than others previously applied. Two-day air parcel back trajectories reaching an unpolluted site in the centre of the northern plateau of the Iberian Peninsula were calculated over a three-year period using the METEX model. A procedure based on the kernel density calculation was applied to the direction of each trajectory centroid to determine groups of trajectories. This method is much faster than the cluster procedure when it comes to retaining the directional details of groups. Seasonal analysis of six groups of trajectories revealed that the Atlantic origin prevailed against displacement from northern Europe. Moreover, Mediterranean and particularly African trajectories were infrequent, probably due to the rough peninsular orography in these directions. The location of air trajectories reaching the study site was described using a surface classification below the air parcels with improved spatial resolution compared to previous analyses. Local contribution was very marked, particularly in summer. Mean trajectories were calculated for each group together with meteorological features and CO2 and CH4 concentrations. Groups may be identified by their mean temperature, wind speed, elevation and distance values. However, only two groups should be considered when analysing the two trace gases, one for trajectories from the Atlantic Ocean and the second for trajectories from the continent. Contrasts of about 4 ppm for CO2 in summer and 0.023 ppm for CH4 in winter were observed, revealing that air trajectories from the Atlantic Ocean were cleaner than those arriving from the continent. These differences were attributed to higher air stagnation over land.

A new ground-based FTIR spectrometer reference site at Shadnagar (India) and preliminary columnar retrievals of CH4 and N2O

ABSTRACTA Fourier Transform Infrared (FTIR) spectrometer has been operational since March 2014, at National Remote Sensing Centre (NRSC), Shadnagar, which is a suburban site of central India. Direct solar radiation spectra recorded by the FTIR during clear sky days at a high spectral resolution of 0.01 cm‒1 were analysed using the line-by-line radiative transfer algorithm (LBLRTA) to retrieve the initial results of column-averaged concentrations of methane (XCH4) and nitrous oxide (XN2O) in the atmosphere. Error residuals between the measured and estimated atmospheric transmissions are in the range of 0.40–0.80% for CH4 and 0.20–0.50% for N2O, respectively. The maximum (minimum) XCH4 and XN2O were, respectively, 1.88 ± 0.04 ppm (1.67 ± 0.02 ppm) and 316.15 ± 5.85 ppb (278.92 ± 4.02 ppb). Columnar concentrations of CH4 and N2O retrieved from the Infrared Atmospheric Sounding Interferometer (IASI) were compared against retrieved XCH4 and XN2O using the ground FTIR. The observed differences between the two data sets lie between −0.06 ppm and +0.10 ppm for CH4 and between +32 ppb and ‒10 ppb for N2O.

Three-gas detection system with IR optical sensor based on NDIR technology

In this paper, a three-gas detection system with a environmental parameter compensation method is proposed based on Non-dispersive infra-red (NDIR) technique, which can be applied to detect multi-gas (methane, carbon dioxide and carbon monoxide). In this system, an IR source and four single-channel pyroelectric sensors are integrated in the miniature optical gas chamber successfully. Inner wall of the chamber coated with Au film is designed as paraboloids. The infrared light is reflected twice before reaching to detectors, thus increasing optical path. Besides, a compensation method is presented to overcome the influence in variation of environment (ambient temperature, humidity and pressure), thus leading to improve the accuracy in gas detection. Experimental results demonstrated that detection ranges are 0–50,000ppm for CH4, 0–44,500ppm for CO, 0–48,000ppm for CO2 and the accuracy is ±0.05%.

Ammonia and greenhouse gas emissions from fattening pig house with two types of partial pit ventilation systems

To reduce the cost of the air purification system in cleaning the exhaust air from pig buildings, a concept of partial pit ventilation (PPV), which applies an extra pit exhaust extracting a part of air directly from emission source zone, was introduced. The objectives of this study are to quantify gaseous emissions from a fattening pig building with PPV, and to assess the performance of the PPV with two types of air inlets (ceiling air inlet, system-C; wall-jet air inlet, system-W). Two trials were carried out under summer and winter conditions. For each trial and in each type of PPV system, 32 fattening pigs were raised. Gas concentrations and climate data were continuously measured. Results showed that the average indoor concentrations were 2.1–3.4ppm for NH3, 0.4–0.6ppm for CH4, and 800–966ppm for CO2 in summer; and 4.2–4.3ppm for NH3, 5.0–5.6ppm for CH4, and 1491–1542ppm for CO2 in winter. N2O releases were rarely observed in the current set-up. The PPV system substantially improved the indoor air quality. Approximately half of the whole NH3 emission (47–63%) was driven through the pit exhausts. A combination of PPV and air purification system is considered to be a practical and efficient mitigation method for gaseous pollution from pig production. The two types of PPV systems resulted in two different kinds of airflow characteristics, which further affected the gaseous release processes. During summer, lower gas concentrations and emissions were found in system-C than in system-W. During winter, system-C gas concentrations were higher in room air and slightly lower in pit air than system-W. Both systems had similar values of emissions during winter. Higher gas concentrations were found in winter than in summer. On average, the winter trial had lower daily NH3 emissions but higher CH4 and CO2 emissions than the summer trial.

Greenhouse gas emissions from naturally ventilated freestall dairy barns

Greenhouse gas (GHG) emissions from two naturally-ventilated dairy freestall barns measured for a total of 21 d, one week each in May, July, and September 2009, are presented in this article. The holding capacity of Barn 1 (B1) was 400 Holstein cows, while that for Barn 2 (B2) was 850 cows. Air samples were taken from inlets and outlets of the barns via a custom made multiplexer gas sampling system for measurement of gas concentrations using a photoacoustic infrared multigas analyzer. Barn ventilation rates were based on air velocity measured with arrays of 3-D ultrasonic anemometers at inlets and outlets. Gas concentrations (10 min means) in the barns ranged from: 443–789 ppm for CO2, 0.0–39.4 ppm for CH4, and 0.25–0.39 ppm for N2O; with mean concentrations ranging from 6 to 20%, 0 to 4%, and 26 to 180% above the average background concentrations for CO2, N2O, and CH4, respectively. The correlations between CO2 and CH4 enhanced concentrations were relatively stronger (R of 0.67–0.74) than between CO2 and N2O enhanced concentrations (R of 0.10–0.20). Environmental conditions did not significantly (p = 0.46) impact the enhanced concentrations of N2O in the barns. All three parameters (T, RH, and v) had significant (p < 0.01) influences on CO2 enhanced concentrations; while only T (p < 0.01) and v (p < 0.01) had significant influences on CH4 enhanced concentrations. Enhanced concentrations of CO2 and CH4 correlated negatively with all three parameters. The influence of the temperature-humidity index (THI) on CO2 enhanced concentrations was higher than that of v; while the effect v had on CH4 enhanced concentrations was slightly higher than that of the temperature-humidity index. The average emissions, based on hourly means, ranged from 5.3 to 10.7 kg d−1 AU−1 for CO2; 0.3 to 2.5 g d−1 AU−1 for N2O; and between 67 and 252 g d−1 AU−1 for CH4. Nitrous oxide emissions from the smaller barn, B1 (0.4–2.5 g d−1 AU−1), were significantly higher than from the larger barn, B2 (0.3–0.5 g d−1 AU−1) most probably because 50% of B1 was open (no stalls) loose dirt floor.

Development of Greenhouse Gas Emission Factors from Sewage Sludge Incinerator

In this study, the researchers have developed the greenhouse gas emission coefficients targeted at sewage sludge incineration plants that treat sewage sludge by incineration. Among the gases emitted from the sewage sludge incineration plants, the greenhouse gases showed concentrations of 6.84% for CO₂, 4.51 ppm for CH₄, and 86.34 ppm for N₂O; calculated into greenhouse gas emission coefficients, these gave 276.06 kg CO₂/ton, 0.0066 kg CH₄/ton, and 0.35 kg N₂O/ton. As the result of calculating the greenhouse gas emission quantity in sewage sludge incineration plants using the greenhouse gas emission coefficients, the gross greenhouse gas emission was 84.63 ton CO₂ eq./day, and the net emission was 23.90 ton CO₂ eq./day; this was 37.52 ton CO₂ eq./day less than the net greenhouse gas emission that was calculated using the standard values of IPCC, which was 61.42 ton CO₂ eq./day. This difference is probably because unlike the standard values of IPCC, the greenhouse gas emission coefficients of this study reflected the special properties of subject facilities. Thus, it is thought that emission coefficient research on the facilities that deviated from the standard values of IPCC should continue to achieve the development of national greenhouse gas coefficient that reflects the special properties of Korea.

Development of super luminescent diode based sensing technique for multiple-gas monitoring

A multiple-gas sensor based on absorption spectroscopy technique using a super luminescent diode source of 1.5 μm is proposed and realized for combustion applications. This technique allows CH4 and CO2 gas sensing in bio-gas plant to monitor the quality of the gas. In this study, a solid Fabry–Perot etalon with a free spectral range of 517 GHz is also used and the detection limit is improved, allowing measurement with lower resolution spectrum analyzer. The detection limit of 292 ppm for C2H2 (at 1,543.7 nm), 4,492 ppm for CH4 (at 1,525.92 nm) and 6.5 % for CO2 (at 1,572.68 nm) is attained for 2 m path length with the spectrum analyser of 0.02 nm resolution. With the use of etalon, nearly the same detection limit is attained for all the species at 1 nm resolution.

Fabrication of mid-infrared hollow-core Bragg fiber and it application in gas sensing

In its application of gas sensing, the transmission band of the hollow-core Bragg fiber should match the main absorption peak of the target gas. In this paper, we introduce the design method of the hollow-core Bragg fiber transmission band and develop a fabrication process supporting its transmission band control. Fiber samples with fundamental transmission bands at 10.6 m and 3.3 m are fabricated, whose transmission losses are 5.9 dB/m and 8.8 dB/m, respectively, measured by the cut-back method. Utilizing the fiber sample with a transmission band of 3.3 m, the injection and the expulsion of CH4/N2 gas are realized and observed by the change of fiber transmission spectrum. The detection limit of the experimental system is measured to be 26 ppm for CH4 by exponential dilution method, demonstrating the feasibility of hollow-core Bragg fiber in its application of gas sensing.

Procedure for Fast Simultaneous Analysis of the Greenhouse Gases: Methane, Carbon Dioxide, and Nitrous Oxide in Air Samples

A comprehensive procedure has been developed and is reported here for (i) sampling air above a soil surface and (ii) analyzing it for the three greenhouse gases: methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). The automated gas‐chromatography procedure simultaneously analyzes for CH4, CO2, and N2O and has a precision of 0.87, 2.17, and 0.74%, respectively. Method-detection limits are 0.04 ppm for CH4, 25.5 ppm for CO2, and 7.4 ppb for N2O. The procedure is used to monitor greenhouse gas exchanges at soil surfaces; its precision and automated ability to analyze large sample numbers produces quality data available for upscaling and modeling for inventory purposes; and it is used for developing a process‐based understanding of the mechanisms controlling greenhouse gas fluxes at the soil surface, which can then be applied to develop mitigation strategies.

PreCon: A Fully Automated Interface for the Pre-Gc Concentration of Trace Gases on Air for Isotopic Analysis

Abstract For the high precision isotope analysis of atmospheric trace gases a computer controlled concentration interface has been developed. From small air samples it collects either N2O or CO2 derived from CH4 at their respective concentrations (0.3 ppm for N2O, 1.7 ppm for CH4) into a small diameter cold trap (−196°C) and interfaces via GC and open split to an isotope ratio mass spectrometer (Finnigan MAT 252) for on-line isotope evaluation. External reproducibilities for repeated measurements of 100 ml air samples from the same source of < 0.2° (δ-notation) have been achieved for 13C/12C from CH4 and for 15N/14N and 18O/16O from N2O. The precision is adequate to monitor the isotopic changes in these gases during a day's course.

95/05259 Characterization of uranium contamination in surface soils

In this paper, a three-gas detection system with a environmental parameter compensation method is proposed based on Non-dispersive infra-red (NDIR) technique, which can be applied to detect multi-gas (methane, carbon dioxide and carbon monoxide). In this system, an IR source and four single-channel pyroelectric sensors are integrated in the miniature optical gas chamber successfully. Inner wall of the chamber coated with Au film is designed as paraboloids. The infrared light is reflected twice before reaching to detectors, thus increasing optical path. Besides, a compensation method is presented to overcome the influence in variation of environment (ambient temperature, humidity and pressure), thus leading to improve the accuracy in gas detection. Experimental results demonstrated that detection ranges are 0–50,000 ppm for CH4, 0–44,500 ppm for CO, 0–48,000 ppm for CO2 and the accuracy is ±0.05%.