Ppm For CH4 Research Articles

Seasonal dynamics and climatic influences of greenhouse gases (CO2, CH4) and ammonia (NH3) concentrations on loose housing cattle shed

Measurement of gas concentrations is crucial for the calculation of emissions from livestock buildings. The study aimed to examine how the concentrations of greenhouse gases (CO2, CH4) and ammonia (NH3) vary seasonally and influenced by climatic conditions in loose housing cattle sheds in India. Two dairy cow sheds with different layouts, floor types, and cleaning practices were selected for measurements during the summer, rainy, and winter seasons. The concentrations of CO2, CH4, and NH3 exhibited significant variations, ranging from 405 to 717 ppm for CO2, 0.01 to 16.12 ppm for CH4, and 0.00 to 1.90 ppm for NH3. The winter season showed higher levels of CO2 and CH4, while NH3 concentrations were higher during the summer season. Notable differences were observed in CO2 and CH4 levels between sheds during feeding, as well as in CO2 levels during cleaning activities. The study revealed a weak correlation between greenhouse gases, ammonia, and climatic conditions in the cattle sheds, except for a moderate positive correlation between CO2 and relative humidity during winter which means other factors such as housing design, facilities and practices play a significant role.

High Sensitivity CH4 and CO2 Gas Sensor Using Fiber Bragg Grating Coated with Single Layer Graphene

This article outlines the development of a Fiber Bragg Grating (FBG) intended for use as a sensor for CH4 and CO2 gases. Following fabrication, the FBG was effectively treated with a layer of Graphene Material through a modified RF Sputtering process. This coating procedure involved introducing argon gas into the chamber and subjecting the FBG, securely held by two vacuum stages, to a temperature range of 27°C to 600°C by adjusting the power supplied to the cathode and anode, ranging from 0 to 125 Watts. Subsequently, the FBG was employed as a key sensing element within an experimental setup aimed at measuring gas concentrations within a confined space. The assessment involved analyzing the reflected signal of the FBG using an Optical Interrogator System, which demonstrated a shift in the Bragg wavelength of the reflected signal corresponding to varying gas concentrations. This study indicates promising outcomes for the Graphene-coated FBG as a gas sensor. The sensor’s sensitivity was evaluated based on the Bragg wavelength shift resulting from gas presence within the chamber. The Graphene-coated FBG exhibited sensitivities of 3.3 ppm for CH4 and 3.7 ppm for CO2, surpassing those reported in prior research efforts.

Trace Analysis of C4F7N Insulating Gas Mixtures by Spontaneous Raman Spectroscopy and Gas Chromatography.

2,3,3,3-Tetrafluoro-2-(trifluoromethyl) propanenitrile (C4F7N) is being researched as an alternative to sulfur hexafluoride (SF6) for applications in gas-insulated switchgear. We independently assessed the effectiveness of gas chromatography-mass spectrometry (GC-MS) and a novel method of feedback-assisted multipass cavity spontaneous Raman spectroscopy (SRS) for the trace quantification of impurities in C4F7N and its related byproducts. A total of 14 gases were identified with estimated concentrations as low as 20 ppm (ppm) for C3F6 using GC-MS and 7.4 ppm for CH4 using SRS and as high as 500 ppm for CF4 using GC-MS and 1430 ppm for CO using SRS. While GC-MS is highly effective in selectively detecting and quantifying trace contaminants, it necessitates separate detectors for various gases, such as CH4 and H2. SRS succeeded in detecting CF4 and C2F6 at concentrations of 465 and 100 ppm, respectively, and in placing an upper bound of several hundred ppm for the other analytes. Crucially, SRS holds potential for portability-and thus for field applications-in gas-insulated switchgear equipment diagnostics.

Simultaneous atmospheric CH4, CO2 and O2 detection using fiber-optic switch (FOS)-based time-division multiplexed NIR laser long optical path absorption spectroscopy

A near-infrared (NIR) distributed feedback (DFB) laser sensor based on long optical path absorption spectroscopy technique was developed for simultaneous measurement of atmospheric methane (CH4), carbon dioxide (CO2) and oxygen (O2). A fiber-optic switch (FOS) in conjunction with the time-division multiplexing (TDM) technique was adopted to enable different lasers scan over the target gas absorption lines in turn. The long optical path wavelength modulation spectroscopy (WMS) technique with second harmonic detection as well as a laser power fluctuation correction method was used to improve the sensor’s precision and accuracy. For the selected gas absorption lines, located at 6046.945 cm-1, 6361.245 cm-1 and 7877.647 cm-1, the detection limit (1σ) of 0.034 parts per million (ppm) for CH4, 11.921 ppm for CO2 and 0.14% for O2 was achieved according to the concentration and noise level. Allan deviation analysis indicates that the 1-s measurement precision was 0.030 ppm for CH4, 11.518 ppm for CO2 and 0.14% for O2, which could be improved to 6.5E-4 ppm, 0.255 ppm and 0.005% at an optimal average time of 800 s. A two-day continuous measurement of the CH4, CO2, and O2 concentration from ambient air was carried out, which verifies the stability and robustness of the developed multi-gas sensor.

Multigas nonresonant photoacoustic spectroscopy sensor based on a broadband radiation source

AbstractMultigas detection is in demand for a wide range of environmental and industrial applications. In this work, a sensitive and selective multigas photoacoustic spectroscopy (MG‐PAS) sensor was developed by employing a nonresonant photoacoustic spectroscopy technique combining a broadband radiation source. Six gases including CO, CO2, CH4, C2H2, C2H4, and C2H6 were selected as target measurement molecules. Selectivity of the MG‐PAS was realized by using six mid‐infrared narrow‐band filters which integrated in a homemade filter wheel. A minimum concentration detection limits of 0.2 ppm for CO, 0.05 ppm for CO2, 0.12 ppm for CH4, 0.1 ppm for C2H2, 0.81 ppm for C2H4, and 0.05 ppm for C2H6 were obtained, respectively, with a 1‐s integration time. Measurements of six gas mixtures showed that the average measurement error of the MG‐PAS sensor was within 2%.

Simultaneous detection of greenhouse gases CH4 and CO2 based on a dual differential photoacoustic spectroscopy system.

In addition to the atmospheric measurement, detection of dissolved carbon oxides and hydrocarbons in a water region is also an important aspect of greenhouse gas monitoring, such as CH4 and CO2. The first step of measuring dissolved gases is the separation process of water and gases. However, slow degassing efficiency is a big challenge which requires the gas detection technology itself with low gas consumption. Photoacoustic spectroscopy (PAS) is a good choice with advantages of high sensitivity, low gas consumption, and zero background, which has been rapidly developed in recent years and is expected to be applied in the field of dissolved gas detection. In this study, a miniaturized differential photoacoustic cell with a volume of 7.9 mL is designed for CH4 and CO2 detection, and a dual differential method with four microphones is proposed to enhance the photoacoustic signal. What we believe to be a new method increases photoacoustic signal by 4 times and improves the signal to noise ratio (SNR) over 10 times compared with the conventional single-microphone mode. Two distributed feedback (DFB) lasers at 1651 nm and 2004nm are employed to construct the PAS system for CH4 and CO2 detection respectively. Wavelength modulation spectroscopy (WMS) and 2nd harmonic demodulation techniques are applied to further improve the SNR. As a result, sensitivity of 0.44 ppm and 7.39 ppm for CH4 and CO2 are achieved respectively with an integration time of 10 s. Allan deviation analysis indicates that the sensitivity can be further improved to 42 ppb (NNEA=4.7×10-10cm-1WHz-1/2) for CH4 and 0.86 ppm (NNEA=5.3×10-10cm-1WHz-1/2) for CO2 when the integration time is extended to 1000 s.

Dual Activation and Photocatalyst-Induced Selective Detection in Defect Tuned Pd–ZnO Thin Films for Low ppm Detection of CH and CO

The selectivity of CO and CH4 remains a hurdle to researchers working on metal-oxide-based sensors, as the sensing mechanism is analogous for both gases. With this objective, an attempt has been made to realize selective sensing of CH4 (up to 1 ppm) and CO (up to 1 ppm) by introducing a selective photocatalyst layer (Zn5(OH)8Cl2.H2O) on Pd–ZnO. It has been noticed that the incorporation of a photocatalytic layer is found to be highly efficacious in providing the sensor with a strong absorption reaction and propelling the surface conversion kinetics. The role of dual activation and photocatalytic activity in selectivity along with tunability is also explored in this work. The dual activation incorporates the benefits of both temperature and optical excitation on metal-oxide-based sensors, highlighting the innumerable advantages and nullifying the disadvantages of both methods. Tunable and selective sensing with a response time/recovery time of 40 s is explicated. The method for improving the sensing performance of Pd–ZnO–photocatalyst-based nanostructures in terms of repeatability and cross sensitivity with respect to 1 ppm of CO, 1 ppm of CH4, 1 ppm of NH3, 250 ppm of CO, and 40% of O2 is discoursed. It has been observed that the sensor with a sensitivity of 23%/ppm for CH4 and 93%/ppm for CO with a minimum baseline drift of less than 3% is achieved. The long-term stability and repeatability of dual-activated sensors are also verified, and less than 3% change has been noticed. The work can be extended for the selectivity of other metal oxides as well.

Geo-Environmental Evaluation of the Kaakia Landfill, Southwest Makkah, Saudi Arabia

The environmental control and management of municipal solid waste (MSW) dumping sites is considered one of the sensitive challenges faced by executive municipalities. This is especially true in Makkah due to the gradual increase in urban population and visitors, with an overall MSW generation of about one million tons per year. Consequently, the geo-environmental evaluation of the Kaakia dumping site shed light on the potential environmental threats, in terms of ambient air quality levels and meteorological parameters, in addition to geophysical inspection. An air quality survey discussed the major trends of ambient air pollutants (SO2, NO2, CO, O3, CH4, and PM10) downwind from the Kaakia dumping site. It indicated the presence of a significant increase in sporadic plumes of Methane concentration. The maximum hourly averages ranged between 22.9–26.6 µg/m3 for SO2, 44.4–64.0 µg/m3 for NO2, 0.86–1.38 mg/m3 for CO, 150.2–158.8 µg/m3 for O3, 5.09–5.9 ppm for CH4, and 955–994 µg/m3 for PM10. The ground penetrating radar (GPR) geophysical survey indicated the subsurface sequence of three geological layers, as confirmed by nearby bores of the investigated site: (1) a surface layer formed of alluvial sediments of sand, which were 2.5–3.1 m thick; (2) a second layer represented by sand and gravel, with a thickness of 4.6–6.5 m; and (3) a third layer equivalent to saturated alluvial sediments mixed with rock fragments that extended to a depth of 13 m. The signals of the GPR were attenuated at the base of the conducted profiles due to the percolation of generated leachate to the subsurface sequence and contaminated groundwater aquifer.

Emission of greenhouse gases due to anthropogenic activities: an environmental assessment from paddy rice fields.

Paddy rice fields (PRFs) are a potent source of global atmospheric greenhouse gases (GHGs), particularly CH4 and CO2. Despite socio-environmental importance, the emission of GHGs has rarely been measured from Haryana agricultural fields. We have used new technology to track ambient concentration and soil flux of GHGs (CH4, CO2, and H2O) near Karnal's Kuchpura agricultural fields, India. The observations were conducted using a Trace Gas Analyzer (TGA) and Soil Flux Smart Chamber over various parts, i.e., disturbed and undisturbed zone of PRFs. The undisturbed zone usually accounts for a maximum ambient concentration of ~ 2434.95ppb and 492.46ppm of CH4 and CO2, respectively, higher than the average global concentration. Soil flux of CH4 and CO2 was highly varied, ranging from 0.18 to 11.73nmolm-2s-1 and 0.13-4.98μmolm-2s-1, respectively. An insignificant correlation was observed between ambient concentration and soil flux of GHGs from PRFs. Waterlogged (i.e., irrigated and rain-fed) soil contributed slightly lower CH4 flux to the atmosphere. Interestingly, such an agricultural field shows low CO2 and CH4 fluxes compared to the field affected by the backfilling of rice husk ash (RHA). This article suggests farmers not mix RHA to increase soil fertility because of their adverse environmental effects. Also, this study is relevant in understanding the GHGs' emissions from paddy rice fields to the atmosphere, their impacts, and mitigating measures for a healthy ecosystem.

Compact Non-Dispersive Infrared Multi-Gas Sensing Platform for Large Scale Deployment with Sub-ppm Resolution

We report on a novel, cost-effective non-dispersive infrared (NDIR) multi-gas sensor aimed at environmental air pollution monitoring. The rugged design of the K96 sensor core combines highest compactness and low-power consumption with our unique multi-channel cell design, featuring the detection of up to three different gases simultaneously, including CO2, CH4, N2O, and H2O. Our sensing platform allows the selection of the target gases as well as the concentration ranges, thus providing highly customizable gas sensor systems targeting application-specific gas monitoring settings. The sensor core comes with an implemented calibration model, and can address in real time any cross-sensitivity between the NDIR gas-sensing channels. We provide an immensely versatile sensing system while ensuring high sensing stability combined with high precision (<0.1 ppm for both CO2 and N2O, <0.5 ppm for CH4). The K96 multi-gas sensor core offers a resilient sensor solution for the increasing demand of compact monitoring systems in the field of environmental monitoring at reasonable costs for medium-to-high volumes.

Simultaneous Detection of CO2 and CH4 Using a DFB Diode Laser-Based Absorption Spectrometer

In this paper, an attractive gas sensing technique based on fiber optical sensing ideal was developed for the detection of multi-gas species simultaneously. Calibration-free laser absorption spectroscopy (LAS) was used and combined with a multi-pass optical absorption cell, two fiber-coupled near-infrared (NIR) distributed feedback (DFB) diode lasers are used and coupled into a single optical path for measuring CO2 and CH4 absorption spectra simultaneously. The optimal sampling pressure, laser tuning characteristics, spectral sampling points, and potential optical interference are theoretically and experimentally investigated in detail. The results indicated that the proposed technique has good reliability and has been successfully demonstrated for ambient CO2 and CH4 detection by using a single sample cell and detector. An Allan–Werle deviation analysis shows that detection limits of 0.12 ppm for CH4 and 35.97 ppm for CO2 can be obtained with an integration time of 181 s and 166 s, respectively. The proposed technique can be expanded to measure more molecules simultaneously by combing laser array and may pave a new way for developing a low-cost and ultra-compact multi-gas laser spectroscopy sensing system.

Simultaneous detection of multiple gases using multi-resonance photoacoustic spectroscopy

In this paper, a gas sensing technique based on multi-resonance photoacoustic spectroscopy (M-PAS) is firstly proposed for simultaneous detection of multi-component gas molecules. To explore the capabilities of this technique, a spherical resonator with multiple resonant modes and high quality factors are detailedly developed by theoretical simulation and experimental analysis. The proposed M-PAS technique combing with wavelength modulation spectroscopy (WMS) is investigated for simultaneous detection of H2O, CO2 and CH4, respectively. Based on Allan-Werle deviation analysis, the detection limits of 1.17 ppm for H2O, 83 ppm for CO2 and 1.76 ppm for CH4, respectively, at the integration time of 136 s, 181 s and 195 s were achieved, corresponding to the normalized noise equivalent absorption (NNEA) coefficient of 6.03 × 10−10 cm−1W/√Hz, 5.46 × 10−10 cm−1W/√Hz, 2.36 × 10−9 cm−1W/√Hz. The reported sensing technique has potential applications in atmospheric environment monitoring, industrial process control and breath gas analysis by appropriate improvements, and can easily be modified for other multi-component gas analysis.

Compact and Versatile QEPAS-Based Sensor Box for Simultaneous Detection of Methane and Infrared Absorber Gas Molecules in Ambient Air

In this work we report on an innovative sensor box employing two acoustic detection modules connected in series for quartz-enhanced photoacoustic multi-gas detection. One detection module is coupled with an internal distributed-feedback quantum cascade laser (DFB-QCL) emitting at ∼7.719 µm for methane (CH4) sensing, while the second module has been designed to be coupled with an external laser source targeting the absorption features of a specific gas molecule Mx in the infrared spectral range. The sensor box can thus be employed for any application, depending on the CH4/Mx gas combination to be detected. The ∼7.719 µm DFB-QCL also allowed water vapor monitoring. To demonstrate the sensor versatility, we report on the QEPAS-box environmental monitoring application by simultaneously detecting in air methane, which is a greenhouse gas, nitric oxide (NO), an ozone depleting substance, and water vapor. Sensitivity levels of 4.30 mV ppm−1 and 17.51 mV ppm−1 and minimum detection limits of 48 ppb and 11 ppb for methane and nitric oxide detection were achieved, respectively. The sensor box operation was tested by analysing ambient air. Average concentrations of ∼1.73 ppm of CH4, ∼0.134 ppm of NO and 1.8% of H2O were measured.

Frequency-Domain Detection for Frequency-Division Multiplexing QEPAS

To achieve multi-gas measurements of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors under a frequency-division multiplexing mode with a narrow modulation frequency interval, we report a frequency-domain detection method. A CH4 absorption line at 1653.72 nm and a CO2 absorption line at 2004.02 nm were investigated in this experiment. A modulation frequency interval of as narrow as 0.6 Hz for CH4 and CO2 detection was achieved. Frequency-domain 2f signals were obtained with a resolution of 0.125 Hz using a real-time frequency analyzer. With the multiple linear regressions of the frequency-domain 2f signals of various gas mixtures, small deviations within 2.5% and good linear relationships for gas detection were observed under the frequency-division multiplexing mode. Detection limits of 0.6 ppm for CH4 and 2.9 ppm for CO2 were simultaneously obtained. With the 0.6-Hz interval, the amplitudes of QEPAS signals will increase substantially since the modulation frequencies are closer to the resonant frequency of a QTF. Furthermore, the frequency-domain detection method with a narrow interval can realize precise gas measurements of more species with more lasers operating under the frequency-division multiplexing mode. Additionally, this method, with a narrow interval of modulation frequencies, can also realize frequency-division multiplexing detection for QEPAS sensors under low pressure despite the ultra-narrow bandwidth of the QTF.

Simultaneous methane and acetylene detection using frequency-division multiplexed laser absorption spectroscopy

A dual-gas optical sensor was developed using frequency-division multiplexed (FDM) scanned-wavelength modulation spectroscopy for simultaneous detection of methane (CH4) and acetylene (C2H2). Two infrared lasers were combined to exploit C2H2 and CH4 absorption lines centered at 6539.45 cm−1 and 6057.09 cm−1, respectively. Scanned-WMS with the second-harmonic detection (WMS-2f) and a compact astigmatic multipass gas cell (36-m path length in a 0.3 L volume) were employed to improve detection sensitivity. Simultaneous dual-gas detection was realized by modulating each laser at a different frequency (5 kHz for 1529 nm and 13 kHz for 1650 nm) and software lock-in amplifiers were used to obtain the corresponding WMS-2f signals from a single photodetector. The Allan deviation analysis was performed to assess the long-term stability and minimum detection limit (MDL) of the sensor system. The MDL of 0.92 ppm for CH4 and 0.64 ppm for C2H2 was achieved at 0.02-s integration time, which can be further improved to 55 ppb for CH4 and 10 ppb for C2H2 at an optimum integration time of 10-s and 15-s, respectively. Such a dual-gas sensor has a promising potential for detecting dissolved gases (CH4 and C2H2) in transformer oil for fault diagnosis due to its high sensitivity, hardware simplicity, and fast temporal resolution.

A Laser-Based Multipass Absorption Sensor for Sub-ppm Detection of Methane, Acetylene and Ammonia.

A compact, sensitive laser-based absorption sensor for multispecies monitoring of methane (CH4), acetylene (C2H2) and ammonia (NH3) was developed using a compact multipass gas cell. The gas cell is 8.8 cm long and has an effective optical path length of 3.0 m with a sampling volume of 75 mL. The sensor is composed of three fiber-coupled distributed feedback lasers operating near 1512 nm, 1532 nm and 1654 nm, an InGaAs photodetector and a custom-designed software for data acquisition, signal processing and display. The lasers were scanned over the target absorption features at 1 Hz. First-harmonic-normalized wavelength modulation spectroscopy (f = 3 kHz) with the second harmonic detection (WMS-2f/1f) is employed to eliminate the unwanted power fluctuations of the transmitted laser caused by aerosol/particles scattering, absorption and beam-steering. The multispecies sensor has excellent linear responses (R2 > 0.997) within the gas concentration range of 1–1000 ppm and shows a detection limit of 0.32 ppm for CH4, 0.16 ppm for C2H2 and 0.23 ppm for NH3 at 1 s response time. The Allan–Werle deviation analysis verifies the long-term stability of the sensor, indicating a minimal detection limit of 20–34 ppb were achieved after 60–148 s integration time. Flow test of the portable multispecies sensor is also demonstrated in this work.

Thermal CO Oxidation and Photocatalytic CO2 Reduction over Bare and M-Al2O3 (M = Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) Cotton-Like Nanosheets.

Aluminum oxide (Al2O3) has abundantly been used as a catalyst, and its catalytic activity has been tailored by loading transition metals. Herein, γ-Al2O3 nanosheets were prepared by the solvothermal method, and transition metals (M = Co, Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au) were loaded onto the nanosheets. Big data sets of thermal CO oxidation and photocatalytic CO2 reduction activities were fully examined for the transition metal-loaded Al2O3 nanosheets. Their physicochemical properties were examined by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction crystallography, and X-ray photoelectron spectroscopy. It was found that Rh, Pd, Ir, and Pt-loading showed a great enhancement in CO oxidation activity while other metals negated the activity of bare Al2O3 nanosheets. Rh-Al2O3 showed the lowest CO oxidation onset temperature of 172 °C, 201 °C lower than that of bare γ-Al2O3. CO2 reduction experiments were also performed to show that CO, CH3OH, and CH4 were common products. Ag-Al2O3 nanosheets showed the highest performances with yields of 237.3 ppm for CO, 36.3 ppm for CH3OH, and 30.9 ppm for CH4, 2.2×, 1.2×, and 1.6× enhancements, respectively, compared with those for bare Al2O3. Hydrogen production was found to be maximized to 20.7 ppm during CO2 reduction for Rh-loaded Al2O3. The present unique pre-screening test results provided very useful information for the selection of transition metals on Al2O3-based energy and environmental catalysts.

Enhanced mid-infrared gas absorption spectroscopic detection using chalcogenide or porous germanium waveguides

Different integrated photonic sensors are investigated for the detection in the mid-infrared region of the two gases namely CO2 and CH4. The three studied structures are ridge waveguides, based both on chalcogenide films (ChG) or porous germanium (PGe) and slot waveguides based on ChG. Waveguide dimensions are optimized to obtain the highest power factor between guided light and gas while maintaining a single mode propagation in the mid-infrared wavelength range. The achievable power factor is 1% in case of ChG ridge-waveguide, 45% for PGe-ridge, and 58% in case of ChG-slot. Extremely low limits of detection (LOD), 0.1 ppm for CO2 at λ = 4.3 μm and 1.66 ppm for CH4 at λ = 7.7 μm are obtained for a ChG slot waveguide, due to the large gas absorption coefficients in the mid-infrared spectral range. For PGe waveguides, low LOD values are also computed: 0.12 ppm for CO2 at λ = 4.3 μm and 1.89 ppm for CH4 at λ = 7.7 μm. These results show that the proposed structures could achieve competitive performance required for generic spectroscopic detection on a chip for environment and health sensing.

New technique for high-precision, simultaneous measurements of CH<sub>4</sub>, N<sub>2</sub>O and CO<sub>2</sub> concentrations; isotopic and elemental ratios of N<sub>2</sub>, O<sub>2</sub> and Ar; and total air content in ice cores by wet extraction

Abstract. Air in polar ice cores provides unique information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas chromatography and mass spectrometry for high-precision, simultaneous measurements of eight air components (CH4, N2O and CO2 concentrations; δ15N, δ18O, δO2∕N2 and δAr∕N2; and total air content) from an ice-core sample of ∼ 60 g. The ice sample is evacuated for ∼ 2 h and melted under vacuum, and the released air is continuously transferred into a sample tube at 10 K within 10 min. The air is homogenized in the sample tube overnight at room temperature and split into two aliquots for mass spectrometric and gas chromatographic measurements. Care is taken to minimize (1) contamination of greenhouse gases by using a long evacuation time, (2) consumption of oxygen during sample storage by a passivation treatment on sample tubes, and (3) fractionation of isotopic ratios with a long homogenization time for splitting. Precision is assessed by analyzing standard gases with artificial ice and duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (1 SD) of duplicate ice-core analyses are 3.2 ppb, 2.2 ppb and 2.9 ppm for CH4, N2O and CO2 concentrations; 0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for δ15N, δ18O, δO2∕N2 and δAr∕N2; and 0.63 mLSTP kg−1 for total air content, respectively. Our new method successfully combines the high-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.

Methane Combustion Using Pd Deposited on CeOx-MnOx/La-Al2O3 Pellistors.

Pd deposited on CeOx-MnOx/La-Al2O3 has been prepared as a sensitive material for methane (CH4) detection. The effect of different amounts (1.25%, 2.5% and 5%) of Pd loading has been investigated. The as prepared materials were deposited on Pt microcoils using a drop-coating method, as a way of developing pellistors operated using a Wheatstone bridge configuration. By spanning the operating temperature range between 300 °C and 550 °C, we established the linearity region as well as the maximum sensitivity towards 4900 ppm of CH4. By making use of the sigmoid dependence of the output voltage signal from the Wheatstone bridge, the gas surface reaction and diffusion phenomena have been decoupled. The pellistor with 5% Pd deposited on CeOx-MnOx/La-Al2O3 exhibited the highest selective-sensitivity in the benefit of CH4 detection against threshold limits of carbon monoxide (CO), sulfur dioxide (SO2) and hydrogen sulfide (H2S). Accordingly, adjusting the percent of Pd makes the preparation strategies of pellistors good candidates towards CH4 detection.