CH4 Measurements Research Articles

Antimethanogenic effects of nitrate supplementation in cattle: A meta-analysis

Supplementing a diet with nitrate is regarded as an effective and promising methane (CH4) mitigation strategy by competing with methanogens for available hydrogen through its reduction of ammonia in the rumen. Studies have shown major reductions in CH4 emissions with nitrate supplementation, but with large variation in response. The objective of this study was to quantitatively investigate the effect of dietary nitrate on enteric CH4 production and yield and evaluate the variables with high potential to explain the heterogeneity of between-study variability using meta-analytical models. A data set containing 56 treatments from 24 studies was developed to conduct a meta-analysis. Dry matter (DM) intake, nitrate dose (g/kg of DM), animal body weight, roughage proportion of diet, dietary crude protein and neutral detergent fiber content, CH4 measurement technique, and type of cattle (beef or dairy) were considered as explanatory variables. Average DM intake and CH4 production for dairy cows (16.2 ± 2.93 kg/d; 311 ± 58.8 g/d) were much higher than for beef cattle (8.1 ± 1.57 kg/d; 146 ± 50.9 g/d). Therefore, a relative mean difference was calculated and used to conduct random-effect and mixed-effect model analysis to eliminate the large variations between types of animal due to intake. The final mixed-effect model for CH4 production (g of CH4/d) had 3 explanatory variables and included nitrate dose, type of cattle, and DM intake. The final mixed-effect model for CH4 yield (g of CH4/kg of DM intake) had 2 explanatory variables and included nitrate dose and type of cattle. Nitrate effect sizes on CH4 production (dairy: -20.4 ± 1.89%; beef: -10.1 ± 1.52%) and yield (dairy: -15.5 ± 1.15%; beef: -8.95 ± 1.764%) were significantly different between the 2 types of cattle. When data from slow-release nitrate sources were removed from the analysis, there was no significant difference in type of cattle anymore for CH4 production and yield. Nitrate dose enhanced the mitigating effect of nitrate on CH4 production and yield by 0.911 ± 0.1407% and 0.728 ± 0.2034%, respectively, for every 1 g/kg of DM increase from its mean dietary inclusion (16.7 g/kg of DM). An increase of 1 kg of DM/d in DM intake from its mean dietary intake (11.1 kg of DM/d) decreased the effect of nitrate on CH4 production by 0.691 ± 0.2944%. Overall, this meta-analysis demonstrated that nitrate supplementation reduces CH4 production and yield in a dose-dependent manner, and that elevated DM intake decreases the effect of nitrate supplementation on CH4 production. Furthermore, the stronger antimethanogenic effect on CH4 production and yield in dairy cows than in beef steers could be related to use of slow-release nitrate in beef cattle.

Successive and automated stable isotope analysis of CO2 , CH4 and N2 O paving the way for unmanned aerial vehicle-based sampling.

RationaleMeasurement of greenhouse gas (GHG) concentrations and isotopic compositions in the atmosphere is a valuable tool for predicting their sources and sinks, and ultimately how they affect Earth's climate. Easy access to unmanned aerial vehicles (UAVs) has opened up new opportunities for remote gas sampling and provides logistical and economic opportunities to improve GHG measurements.MethodsThis study presents synchronized gas chromatography/isotope ratio mass spectrometry (GC/IRMS) methods for the analysis of atmospheric gas samples (20‐mL glass vessels) to determine the stable isotope ratios and concentrations of CO2, CH4 and N2O. To our knowledge there is no comprehensive GC/IRMS setup for successive measurement of CO2, CH4 and N2O analysis meshed with a UAV‐based sampling system. The systems were built using off‐the‐shelf instruments augmented with minor modifications.ResultsThe precision of working gas standards achieved for δ13C and δ18O values of CO2 was 0.2‰ and 0.3‰, respectively. The mid‐term precision for δ13C and δ15N values of CH4 and N2O working gas standards was 0.4‰ and 0.3‰, respectively. Injection quantities of working gas standards indicated a relative standard deviation of 1%, 5% and 5% for CO2, CH4 and N2O, respectively. Measurements of atmospheric air samples demonstrated a standard deviation of 0.3‰ and 0.4‰ for the δ13C and δ18O values, respectively, of CO2, 0.5‰ for the δ13C value of CH4 and 0.3‰ for the δ15N value of N2O.ConclusionsResults from internal calibration and field sample analysis, as well as comparisons with similar measurement techniques, suggest that the method is applicable for the stable isotope analysis of these three important GHGs. In contrast to previously reported findings, the presented method enables successive analysis of all three GHGs from a single ambient atmospheric gas sample.

In Situ Aircraft Measurements of CO2 and CH4: Mapping Spatio-Temporal Variations over Western Korea in High-Resolutions

A cavity ring-down spectroscopy (CRDS) G-2401m analyzer onboard a Beechcraft King Air 350, a new Korean Meteorological Administration (KMA) research aircraft measurement platform since 2018, has been used to measure in situ CO2, CH4, and CO. We analyzed the aircraft measurements obtained in two campaigns: a within-boundary layer survey over the western Republic of Korea (hereafter Korea) for analyzing the CO2 and CH4 emission characteristics for each season (the climate change monitoring (CM) CM mission), and a low altitude survey over the Yellow Sea for monitoring the pollutant plumes transported into Korea from China (the environment monitoring (EM) mission). This study analyzed CO2, CH4, and CO data from a total of 14 flights during 2019 season. To characterize the regional combustion sources signatures of CO2 and CH4, we calculated the short-term (1-min slope based on one second data) regression slope of CO to CO2 and CH4 to CO enhancements (subtracted with background level, present as ∆CO, ∆CO2, and ∆CH4); slope filtered with correlation coefficients (R2) (<0.4 were ignored). These short-term slope analyses seem to be sensitive to aircraft measurements in which the instrument samples short-time varying mixtures of different air masses. The EM missions all of which were affected by pollutants emitted in China, show the regression slope between ∆CO and ∆CO2 with of 1.8–6% and 0.3–0.7 between ∆CH4 and ∆CO. In particular, the regression slope between ∆CO and ∆CO2 increased to >4% when air flows from east-central China such as Hebei, Shandong, and Jiangsu provinces, etc., sustained for 1–3 days, suggesting pollutants from these regions were most likely characterized by incomplete fossil fuel combustions at the industries. Over 80% of the observations in the Western Korea missions were attributed to Korean emission sources with regression slope between ∆CO and ∆CO2 of 0.5–1.9%. The CO2 emissions hotspots were mainly located in the north-Western Korea of high population density and industrial activities. The higher CH4 were observed during summer season with the increasing concentration of approximately 6% over the background level, it seems to be attributed to biogenic sources such as rice paddies, landfill, livestock, and so on. It is also noted that occurrences of high pollution episodes in North-Western Korea are more closely related to the emissions in China than in Korea.

Temporal and spatial variations in methane emissions from the littoral zone of a shallow mid-latitude lake with steady methane bubble emission areas

Temporal and spatial variations in methane (CH4) emissions from the littoral zone of a shallow mid-latitude lake, Lake Suwa, were examined using the eddy covariance technique. The observation data were supplemented with dissolved CH4 measurement and incubation experiments of lake sediment and water. This lake had areas with steady bubble CH4 emissions, shaping the spatial variation in CH4 flux with strong spot emissions. In the other areas, CH4 was emitted via diffusion and episodic ebullition. CH4 emissions from this area had a clear seasonal variation, reflecting temperature variations, with a maximum monthly mean emission of 0.39 µmolm−2s−1 in August. The higher emission in summer was due to higher CH4 production in the sediment and the resulting higher dissolved CH4 concentration in the surface water. The steady bubble CH4 emission was seasonally controlled by the total hydrostatic pressure, with higher emission under lower pressure, suggesting regulation of the amount of bubbles emitted from the lake bottom by pressure. Isotope analysis revealed that this CH4 was produced biologically. This natural gas seepage was estimated to emit 1.9 Mg of CH4 annually. Compared with other eddy covariance studies over inland waters, CH4 emissions from Lake Suwa may be large for the latitude. This may be related to eutrophication, which enhances CH4 production.

Measurements show that marginal wells are a disproportionate source of methane relative to production

ABSTRACT Oil and natural gas wells are a prominent source of the greenhouse gas methane (CH4), but most measurements are from newer, high producing wells. There are nearly 700,000 marginal “stripper” wells in the US, which produce less than 15 barrels of oil equivalent (BOE) d−1. We made direct measurements of CH4 and volatile organic carbon (VOC) emissions from marginal oil and gas wells in the Appalachian Basin of southeastern Ohio, all producing < 1 BOE d−1. Methane and VOC emissions followed a skewed distribution, with many wells having zero or low emissions and a few wells responsible for the majority of emissions. The average CH4 emission rate from marginal wells was 128 g h−1 (median: 18 g h−1; range: 0– 907 g h−1). Follow-up measurements at five wells indicated high emissions were not episodic. Some wells were emitting all or more of the reported gas produced at each well, or venting gas from wells with no reported gas production. Measurements were made from wellheads only, not tanks, so our estimates may be conservative. Stochastic processes such as maintenance may be the main driver of emissions. Marginal wells are a disproportionate source of CH4 and VOCs relative to oil and gas production. We estimate that oil and gas wells in this lowest production category emit approximately 11% of total annual CH4 from oil and gas production in the EPA greenhouse gas inventory, although they produce about 0.2% of oil and 0.4% of gas in the US per year. Implications: Low producing marginal wells are the most abundant type of oil and gas well in the United States, and a surprising number of them are venting all or more of their reported produced gas to the atmosphere. This makes marginal wells a disproportionate greenhouse gas emissions source compared to their energy return, and a good target for environmental mitigation.

Occurrence and origin of groundwater methane in the Stellarton Basin, Nova Scotia, Canada

Groundwater methane (CH4) in areas of fossil fuel development has been a recent focus of study as high CH4 concentrations pose water quality concerns and potential explosive hazards. In 2013, a provincial study in Nova Scotia identified areas with elevated groundwater CH4. However, due to limited data, the specific sources and local distribution of CH4 in those areas remain unknown. In this study, we examined the Stellarton Basin in central Nova Scotia, Canada, a region with an abundance of coal formations, numerous abandoned coal mines, and an active open pit coal mine. Methane was detected in 94% of water samples that were sampled from 45 private water wells. Six water wells exceeded the 28 mg/L hazard mitigation threshold with CH4 levels of up to 72.7 mg/L. The δ13CCH4 (−85.5 to −48.5‰) and the δ2HCH4 (−280 to −88‰) indicated that >95% of samples had CH4 of microbial origin. However, the detection of ethane (C2H6) up to 2.97 mg/L and propane (C3H8) up to 0.008 mg/L, as well as the δ13CC2H6 values (−30.1 to −15.6‰) suggested a mixture of microbial CH4 with trace thermogenic gas, likely migrated from Stellarton coals (δ13CC2H6 of −27.6 to −15.35‰). A mobile greenhouse gas analyzer survey was conducted within the perimeter of residences and off-gassing from taps had atmospheric CH4 measurements as high as 66 ppmv. This study integrates multiple sampling and monitoring methods to investigate groundwater CH4 in a coal-bearing region. The findings advance the understanding of the origin and occurrence of CH4 in complex groundwater systems. The data acquired in this study may be used as a pre-drill baseline for groundwater CH4 concentrations and origins should coal-bed methane operations in Nova Scotia proceed in the future.

Statistical urban plume analysis using observations and air mass modelling at a rural station in the northern Spanish plateau

The influence of urban plumes on the final measurements recorded at rural stations is an issue which has rarely been touched upon in great detail. A better knowledge of local and regional sources of atmospheric CO2 and CH4 evolution over time and space provides policy-makers with the right awareness when acting to improve air quality. Assessing the links between air pollutant mixing ratios and wind direction data can help to identify possible sources. Using the Lagrangian METEX model, the current paper’s main motivation is to identify the impact of the Valladolid urban plume on the final CO2 and CH4 high-precision measurements recorded with a Picarro analyser at a rural station in the upper Spanish plateau (CIB station). The current paper is based on a statistical approach in which multiyear CO2 and CH4 observations are interpreted by means of different statistics and distribution functions. Higher values were detected for both CO2 and CH4 in southern sectors, showing the effect which the Valladolid plume has on final CO2 and CH4 measurements. In addition, six different distribution functions were applied to the dataset and provided satisfactory contrasts with experimental values obtained using Pearson correlation and r critical values. Results indicate that CO2 and CH4 data fitted the Gamma, the Gumbel, and the Lognormal distributions best.

Technical note: Facilitating the use of low-cost methane (CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) sensors in flux chambers – calibration, data processing, and an open-source make-it-yourself logger

Abstract. A major bottleneck regarding the efforts to better quantify greenhouse gas fluxes, map sources and sinks, and understand flux regulation is the shortage of low-cost and accurate-enough measurement methods. The studies of methane (CH4) – a long-lived greenhouse gas increasing rapidly but irregularly in the atmosphere for unclear reasons, and with poorly understood source–sink attribution – suffer from such method limitations. This study presents new calibration and data processing approaches for use of a low-cost CH4 sensor in flux chambers. Results show that the change in relative CH4 levels can be determined at rather high accuracy in the 2–700 ppm mole fraction range, with modest efforts of collecting reference samples in situ and without continuous access to expensive reference instruments. This opens possibilities for more affordable and time-effective measurements of CH4 in flux chambers. To facilitate such measurements, we also provide a description for building and using an Arduino logger for CH4, carbon dioxide (CO2), relative humidity, and temperature.

Study on Products from Fuel-rich Methane Combustion near Sooting Limit Temperature Region and Importance of Methyl Radicals for the Formation of First Aromatic Rings

ABSTRACT Productions of mono-/di-cyclic aromatic hydrocarbons as well as smaller stable species from extremely fuel-rich CH4/air mixtures (equivalence ratio of 1.7–6.0 and fuel-to-mixture ratio of 15–38 mol.%) near sooting limit in terms of temperature, were investigated using a micro flow reactor with a controlled temperature profile at maximum wall temperature of 1300 K. Species measurements of O2, H2, CO, CO2, CH4, C2H2, C2H4, C2H6, benzene, toluene, styrene and naphthalene were performed with GC and GC/MS analysis. One-dimensional computations were also conducted with several detailed chemical kinetics. Most of the mechanisms comparably well predicted the smaller species except C2H2 (acetylene), which was overestimated by all the mechanism especially at moderate equivalence ratio (Ø 3.0). There were large discrepancies between measured and computed mole fractions of benzene and naphthalene at high equivalence ratio (Ø 4.0). Reaction path analysis indicated that reaction pathway branched from C2H3 reacting with methyl radical, which competes with C2H2 production, showed relatively low contribution to benzene formation at moderate equivalence ratio. Therefore, improvements of chemical kinetics with further consideration of reactions with methyl radical are necessary for precise prediction of products where abundant amounts of methyl radical exist.

Comparative study of oxygen-limited and methane-limited growth phenotypes of Methylomicrobium buryatense 5GB1

Methylomicrobium buryatense 5 GB1 has been identified as a promising biocatalyst for industrial methane conversion to produce value-added products. However, despite recent advancements in understanding the metabolism of 5 GB1, existing knowledge on the differences between oxygen-limited and methane-limited phenotypes is still limited. In this work, both batch and continuous experiments were carried out to systematically examine the strain’s oxygen-limited and methane-limited phenotypes. Total carbon balances were performed to ensure the obtained measurements of CH4 and O2 consumption rates and CO2 production rate were accurate. Our results showed that the feed gas composition alone does not dictate the strain’s growth phenotype. In order to achieve a desired phenotype, both feed gas composition and cell growth rate have to be controlled. In addition, contrary to the common belief that oxygen-limited conditions lead to increased production of organic compounds, our results suggest that it is the methane-limited condition that has higher yield for organic compounds. Knowledge of these differences could provide key understanding into how M. buryatense 5 GB1 regulate its carbon flow among different pathways under different growth conditions, which will provide the key insights for both mutant design and process design (e.g., culture conditions) for desired outcomes such as increased production of organic acids. Finally, using data collected in this work and those published in literature, we further validated a published genome-scale model under optimal growth condition. In addition, our results suggest that the current model lacks key metabolic routes to explain the surprisingly robust growth exhibited by the strain under wide substrate availability conditions.

In situ measurement of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; from aircraft over northeast China and comparison with OCO-2 data

Abstract. Several satellites have been launched to monitor the increasing concentrations of greenhouse gases, especially CO2 and CH4 in the atmosphere, through backscattered hyperspectral radiance in the shortwave infrared (SWIR) band. The vertical profiles of greenhouse gases and aerosols could strongly affect the results from these instruments. To investigate the effects of the vertical distribution of CO2 on the uncertainty of SWIR satellite retrieval results, we conducted observations of the vertical profiles of CO2, CH4 and aerosol particles at 0.6–7 km above sea level using a Beechcraft King Air 350ER in Jiansanjiang (46.77∘ N, 131.99∘ E), Heilongjiang Province, northeast China, on 7–12 August 2018. The profiles from this aircraft captured a decrease in CO2 from 2 km to the minimum altitude due to the absorption of vegetation at the surface in summer. CH4 measurements showed about a 0.2 ppm increase from 2.0 to 0.6 km on 10 August, which may result from emissions from the large area of paddy fields below, and a constant mole fraction between 1.951 and 1.976 ppm was recorded at 2 km and above. Comparison of CO2 profiles from a new version of the carbon cycle data assimilation system Tan-Tracker (v1), retrievals from OCO-2 and aircraft measurements was conducted. The results from OCO-2 and the assimilation model system Tan-Tracker captured the vertical structure of CO2 above 3 km, whereas below 3 km the values from OCO-2 and the Tan-Tracker model were lower than those from in situ measurements. Column-averaged CO2 volume mole fractions calculated from in situ measurements showed biases of -4.68±0.44 ppm (-1.18±0.11%) compared to OCO-2 retrievals.

Morpho-acoustic characterization of a shallow-water mud volcano offshore Scoglio d'Affrica (Northern Tyrrhenian Sea) responsible for a violent gas outburst in 2017

A violent gas outburst occurred offshore the Scoglio d'Affrica islet (Tuscan Archipelago, Northern Tyrrhenian Sea) on March 16th 2017, with local fishermen observing columns of dirty water rising up to 10 m above the sea surface. The integration of video footage and dissolved CH4 measurements collected 5 days after the event with high-resolution multibeam data collected 4 months later, allowed us to characterize the source area of the outburst, corresponding to a shallow-water mud volcano. The mud volcano covers an area of ca. 170,000 m2, has a vertical relief of ca. 30 m with respect to the surrounding seafloor and an estimated volume of ca. 1 × 106 m3, based on bathymetric reconstruction. The elongated NNW-SSE shape of the mud volcano is compatible with local structural trends, indicating a tectonic control for its development. The mud volcano is made up of two mounds whose tops are located at a depth of ca. 10 m. The southern mound was responsible for the 2017 outburst, as testified by a 15–20 m wide circular crater on its summit where a large amount of mud breccia and diffuse seepage from small pockmarks were observed in video footage . The flanks of the mud volcano are steep and characterized in the upper part by a hummocky morphology and multiple sediment flows on the western flank.The characterization of the mud volcano and the deposits associated with the 2017 gas outburst provides insight into seafloor-shaping processes linked to fluid seepage in shallow-water sectors. This is a particularly relevant issue considering both the paucity of studies on shallow-water mud volcanoes as well as the hazard associated with violent gas outbursts in such settings, as witnessed by the March 16th 2017 event.

Continuous methane concentration measurements at the Greenland ice sheet–atmosphere interface using a low-cost, low-power metal oxide sensor system

Abstract. In this paper, the performance of a low-cost and low-power methane (CH4) sensing system prototype based on a metal oxide sensor (MOS) sensitive to CH4 is tested in a natural CH4-emitting environment at the Greenland ice sheet (GrIS). We investigate if the MOS could be used as a supplementary measurement technique for monitoring CH4 emissions from the GrIS with the scope of setting up a CH4 monitoring network along the GrIS. The performance of the MOS is evaluated on the basis of simultaneous measurements using a cavity ring-down spectroscopy (CRDS) reference instrument for CH4 over a field calibration period of approximately 100 h. Results from the field calibration period show that CH4 concentrations measured with the MOS are in very good agreement with the reference CRDS. The absolute concentration difference between the MOS and the CRDS reference values within the measured concentration range of approximately 2–100 ppm CH4 was generally lower than 5 ppm CH4, while the relative concentration deviations between the MOS and the CRDS were generally below 10 %. The calculated root-mean-square error (RMSE) for the entire field calibration period was 1.69 ppm (n=37 140). The results confirm that low-cost and low-power MOSs can be effectively used for atmospheric CH4 measurements under stable water vapor conditions. The primary scientific importance of the study is that it provides a clear example of how the application of low-cost technology can enhance our future understanding on the climatic feedbacks from the cryosphere to the atmosphere.

A Review of Enteric Methane Emission Measurement Techniques in Ruminants.

Simple SummaryEnteric methane emissions from ruminants are a major contributor to atmospheric greenhouse gas accumulation in agricultural production systems, which may consequently contribute to climate change. Accurate measurement of methane production in ruminants is vital to develop robust national greenhouse gas emission inventories and to evaluate mitigation strategies of methane emissions. This review summarizes several common methane measurement techniques suitable for ruminant production and discusses the advantages and disadvantages of each method. There is not a perfect technique for all situations. The appropriate technique depends on the objectives and resources available. Sophisticated techniques such as respiration chambers, sulphur hexafluoride tracer and ventilated hood are usually highly accurate but labor and time intensive. Simplified techniques such as GreenFeed, sniffer method, facemask, laser methane detector and portable accumulation chamber may be less accurate but are rapid with a high throughput. In general, an understanding of measurement mechanisms and the advantages and disadvantages with an appreciation of animal behavior and welfare is necessary for all techniques.To identify relationships between animal, dietary and management factors and the resulting methane (CH4) emissions, and to identify potential mitigation strategies for CH4 production, it is vital to develop reliable and accurate CH4 measurement techniques. This review outlines various methods for measuring enteric CH4 emissions from ruminants such as respiration chambers (RC), sulphur hexafluoride (SF6) tracer, GreenFeed, sniffer method, ventilated hood, facemask, laser CH4 detector and portable accumulation chamber. The advantages and disadvantages of these techniques are discussed. In general, RC, SF6 and ventilated hood are capable of 24 h continuous measurements for each individual animal, providing accurate reference methods used for research and inventory purposes. However, they require high labor input, animal training and are time consuming. In contrast, short-term measurement techniques (i.e., GreenFeed, sniffer method, facemask, laser CH4 detector and portable accumulation chamber) contain additional variations in timing and frequency of measurements obtained relative to the 24 h feeding cycle. However, they are suitable for large-scale measurements under commercial conditions due to their simplicity and high throughput. Successful use of these techniques relies on optimal matching between the objectives of the studies and the mechanism of each method with consideration of animal behavior and welfare. This review can provide useful information in selecting suitable techniques for CH4 emission measurement in ruminants.

Environmental Monitoring of Methane with Quartz-Enhanced Photoacoustic Spectroscopy Exploiting an Electronic Hygrometer to Compensate the H2O Influence on the Sensor Signal.

A dual-gas sensor based on the combination of a quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor and an electronic hygrometer was realized for the simultaneous detection of methane (CH4) and water vapor (H2O) in air. The QEPAS sensor employed an interband cascade laser operating at 3.34 μm capable of targeting a CH4 absorption line at 2988.8 cm−1 and a water line at 2988.6 cm−1. Water vapor was measured with both the electronic hygrometer and the QEPAS sensor for comparison. The measurement accuracy provided by the hygrometer enabled the adjustment of methane QEPAS signal with respect to the water vapor concentration to retrieve the actual CH4 concentration. The sensor was tested by performing prolonged measurements of CH4 and H2O over 60 h to demonstrate the effectiveness of this approach for environmental monitoring applications.

Impact of H2O on atmospheric CH4 measurement in near-infrared absorption spectroscopy.

A distributed-feedback (DFB) diode laser based near-infrared absorption spectrometer was used to study H2O broadening coefficients for methane (CH4) transitions at 1.653μm, which contains well-characterized and relatively isolated transitions of appropriate line strengths for sensitive atmospheric CH4 detection. The influence of H2O broadening on R3 transitions of CH4 at 6046.9cm-1 was experimentally investigated in detail. The results indicate that H2O broadening coefficients are approximately 1.3 times higher than the corresponding air-broadening parameters. Based on the measured H2O induced broadening coefficients, the influence of H2O on actual measurement of atmospheric CH4 in tunable diode laser absorption spectroscopy was theoretically and experimentally discussed and compared, and a good agreement was obtained. The experimental results proved that the difference between air- and H2O-broadenings cannot be neglected for high precision gas concentration measurement, especially in a highly humid environment.

Applicability of a gas analyzer with dual quantum cascade lasers for simultaneous measurements of N2O, CH4 and CO2 fluxes from cropland using the eddy covariance technique

We evaluated the applicability of a closed-path gas analyzer with two mid-infrared quantum cascade lasers (QCLs) for simultaneous measurement of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes from a cropland using the eddy covariance (EC) technique. The measurements were carried out in a typical vegetable field in the subtropical China during the wintertime, when the gas fluxes are at their lowest level in the year. A new approach was proposed to optimize the determination of lag times between the wind and gas concentration data, which was proven efficient to increase the reliability of the measured fluxes when the gas exchanges are weak. The dual-QCL analyzer showed a median precision (1σ) of 0.14 nmol mol−1 for N2O, 3.3 nmol mol−1 for CH4 and 0.36 μmol mol−1 for CO2 at sampling frequency of 10 Hz under the field conditions. Such precisions are better than, or comparable with, those of other commonly used closed-path or open-path gas analyzers, which are capable of measuring ony one or two ot the three gases. The detection limit of the EC system for measuring half-hourly fluxes were 0.05 nmol m−2 s−1 for N2O, 1.12 nmol m−2 s−1 for CH4 and 0.14 μmol m−2 s−1 for CO2. The results showed that 100% of the N2O, 85% of the CH4 and 96% of the CO2 fluxes were larger than the above detection limits. This study suggests that the EC technique using a closed-path gas analyzer with two quantum cascade lasers is qualified for reliable and simultaneous measurements of N2O, CH4 and CO2 fluxes from a subtropical cropland throughout the year. Moreover, EC method based on this type of gas analyzer provides an additional option for long-term and simultaneous flux measurements of the three greenhouse gases in a wide range of agricultural and natural ecosystems.

Nuclear Magnetic Resonance to Detect Rumen Metabolites Associated with Enteric Methane Emissions from Beef Cattle

This study presents the application of metabolomics to evaluate changes in the rumen metabolites of beef cattle fed with three different diet types: forage-rich, mixed and concentrate-rich. Rumen fluid samples were analysed by 1H-NMR spectroscopy and the resulting spectra were used to characterise and compare metabolomic profiles between diet types and assess the potential for NMR metabolite signals to be used as proxies of methane emissions (CH4 in g/kg DMI). The dataset available consisted of 128 measurements taken from 4 experiments with CH4 measurements taken in respiration chambers. Predictive modelling of CH4 was conducted by partial least squares (PLS) regression, fitting calibration models either using metabolite signals only as predictors or using metabolite signals as well as other diet and animal covariates (DMI, ME, weight, BW0.75, DMI/BW0.75). Cross-validated R2 were 0.57 and 0.70 for the two models respectively. The cattle offered the concentrate-rich diet showed increases in alanine, valerate, propionate, glucose, tyrosine, proline and isoleucine. Lower methane yield was associated with the concentrate-rich diet (p < 0.001). The results provided new insight into the relationship between rumen metabolites, CH4 production and diets, as well as showing that metabolites alone have an acceptable association with the variation in CH4 production from beef cattle.

Novel gas-phase sensing scheme using fiber-coupled off-axis integrated cavity output spectroscopy (FC-OA-ICOS) and cavity-reflected wavelength modulation spectroscopy (CR-WMS)

By feeding back the reflected light from the first cavity mirror to a single-/multi-pass gas cell via a multi-mode fiber, we demonstrated a novel gas-phase analytical scheme for methane (CH4) detection by combing fiber-coupled off-axis integrated cavity output spectroscopy (FC-OA-ICOS) and cavity-reflected wavelength modulation spectroscopy (CR-WMS). This scheme has an electrical module and two optical sensing modules which are connected through both single- and multi-mode optical fibers. Long-distance gas sensing application was conducted for verifying the analytical ability of the demonstrated technique exploiting the two fiber-coupled optical modules. A detection limit of 3 parts-per-million in volume (ppmv) for an 84 s averaging time and a precision of 56 ppmv for a 150 s averaging time were achieved using FC-OA-ICOS and CR-WMS, respectively. Two different CH4 measurement ranges were achieved in the sensor system with a wide dynamic range from ~15 ppmv to ~12% for CH4 detection. Field monitoring of CH4 leakage was performed for environmental analysis under a static and mobile mode using the wireless-controlled vehicle-mounted gas sensor. The proposed gas sensing scheme with fiber-coupled dual optical modules demonstrates a good potential for long-distance field CH4 measurements, especially for those in hazardous environment where in-situ human observation is impossible.

Wintertime CO2, CH4, and CO Emissions Estimation for the Washington, DC-Baltimore Metropolitan Area Using an Inverse Modeling Technique.

Since greenhouse gas mitigation efforts are mostly being implemented in cities, the ability to quantify emission trends for urban environments is of paramount importance. However, previous aircraft work has indicated large daily variability in the results. Here we use measurements of CO2, CH4, and CO from aircraft over 5 days within an inverse model to estimate emissions from the DC-Baltimore region. Results show good agreement with previous estimates in the area for all three gases. However, aliasing caused by irregular spatiotemporal sampling of emissions is shown to significantly impact both the emissions estimates and their variability. Extensive sensitivity tests allow us to quantify the contributions of different sources of variability and indicate that daily variability in posterior emissions estimates is larger than the uncertainty attributed to the method itself (i.e., 17% for CO2, 24% for CH4, and 13% for CO). Analysis of hourly reported emissions from power plants and traffic counts shows that 97% of the daily variability in posterior emissions estimates is explained by accounting for the sampling in time and space of sources that have large hourly variability and, thus, caution must be taken in properly interpreting variability that is caused by irregular spatiotemporal sampling conditions.