Measurements Of Methane Concentrations Research Articles

Influence of Water Solubility, Phase Equilibria, and Capillary Pressure on Methane Occurence in Sediments: ABSTRACT

Microbial methane is generated in rapidly accumulating marine sediments (>40 m/my) where pore waters are deficient in dissolved oxygen and sulfate. Based on indirect geochemical evidence, microbial methane generation is largely confined to depths of between 10 and 1000 meters beneath the sea floor. Under shelf conditions (water depth <200 m), methane concentrations can exceed solubility in pore water and accumulate as free gas, or escape the sediment as bubbles, or be oxidized in surface sediments. Under some deeper-water conditions of continental slope and rise sediments, more of the methane can be retained and buried because of increased solubility, and because methane in excess of solubility can be stabilized as methane hydrate. Few direct measurements of methane concentration in subsurface pore waters have been made. However, methane-water phase transitions (gas-water contacts, base of gas hydrate reflector) on seismic records can be used with methane solubility relationships to estimate gas contents of sediments. Comparison of various environments shows a relatively narrow range of dissolved methane contents. In marine sediments, free gas (and methane hydrate) is stable only in contact with methane-saturated pore water. Finer-grained sediments can be supersaturated with respect to a gas (and gas hydrate ) phase because of capillarymore » pressure inhibition of bubble (or hydrate ) formation. The amount of methane dissolved in marine sediment pore water is necessarily larger than that present as gas hydrate.« less

Quasi-Continuous Wave Stimulated Raman Technique for Local Methane Concentration Measurements at Atmospheric Pressure

We report the application of quasi-continuous wave (cw) inverse stimulated Raman spectroscopy (SRS) to the quantitative measurement of methane concentrations in atmospheric mixtures near room temperature. The quasi-cw SRS signal, with the use of the v1, fundamental of methane (2916 cm−1), is shown to be proportional to the powers of both the pump and probe lasers as well as to the methane concentration. The current minimum detectable signal corresponds to ∼200 ppm (v/v).

Landfill Gas Migration—Field Investigations At Skellingsted Landfill, Denmark

The background for a landfill gas explosion accident which happened at Skellingsted Landfill in Denmark was investigated. To understand the behaviour of the lateral migrating landfill gas in the area where the accident occurred, an intensive investigation was carried out after the explosion accident measuring time-series of gas composition in 30 wells over a 35-day period. The changes in gas composition in selected wells following a decrease in barometric pressure were measured over a 33-h period. The maximal distance for measured methane concentrations above 5% (vol.) in the pore gas was 90 m. The investigations showed that changes in barometric pressure have a great impact on the pore gas composition. Indications of methane oxidation were observed down to 2 m below ground in distances of more than 60 m from the landfill.

Factors affecting methane emission from rice paddies

A comparative study of rice paddies and the uncovered water field in Taoyuan(Hunan) showed that methane emission from rice-vegetated paddy fields in 1993 was different from that in 1992 (i. e., lower in rates and irregular in pattern). Climate has obvious influence on methane emission. And ebullition made a considerable contribution to the total flux of methane emission from rice paddies (45%). This implies that the intensification of paddy cultivation of rice might not be, as was proposed, the main contributor to the observed gradual increasing of atmospheric methane. 24-hour automatic measurements of atmospheric temperature, air temperature and methane concentration in the static sampling boxes revealed that temperature, in addition to fertilization and irrigation style, is one of the most important factors that control the emission of methane from rice paddies.

Basin Modeling, Methane and Nitrogen Generation, and Migration Problems; Industry Cooperation with Research at KFA Julich: ABSTRACT

Research definition and selection of projects at the Institute of Petroleum and Organic Geochemistry (KFA Juelich) have always been driven by the need of industry. This poster presents a summary of three studies involving industry collaboration. Gas Generation in the West Siberian Basin and Atmospheric Methane Balance: This collaborative project at KFA Juelich and VNII Geosystems (Moscow) with a Russian gas company (Urengoy Neft Gas Geologiya) is funded by several German gas companies (Ruhrgas, Veba and Wintershall). The objective is the understanding of methane generation and accumulation in the crust, and methane release to the atmosphere. The area chosen for study in NW Siberia contains the largest gas fields on earth and supplies a large portion of natural gas used in Germany. Measurements of soil gas emanation rates and in-flight atmospheric methane concentrations are used to calculate the methane balance between lithosphere and atmosphere and possibly anthropogenic pollution (pipeline leaks, etc.). Nitrogen-Rich Natural Gas in the North German Basin - Origin, Kinetics and Numerical Simulation: Many gas reservoirs in the North German Basin contain high concentration ( 90%) of nitrogen, making these accumulations non-commercial. Pyrolysis of Carboniferous coals showed that not only methane but also significant amounts ofmore » nitrogen are generated from the coaly organic matter. Using these pyrolysis kinetics in a basin modelling study, nitrogen concentrations were predicted which closely correlate with observed nitrogen concentrations. German-Norwegian Geoscientific Cooperation: The main goals of this joint effort between the Norwegian and German petroleum industry and research organizations are to: understand and reconstruct the processes involved in the dynamic evolution of the lithosphere; promote the collaboration of scientists of different background; address open questions of basin evolution and reservoir formation in a common study area (North Sea).« less

Landfill gas migration—Field investigations at Skellingsted landfill, Denmark

The background for a landfill gas explosion accident which happened at Skellingsted Landfill in Denmark was investigated. To understand the behaviour of the lateral migrating landfill gas in the area where the accident occurred, an intensive investigation was carried out after the explosion accident measuring time-series of gas composition in 30 wells over a 35-day period. The changes in gas composition in selected wells following a decrease in barometric pressure were measured over a 33h period. The maximal distance for measured methane concentrations above 5% (vol.) in the pore gas was 90 m. The investigations showed that changes in barometric pressure have a great impact on the pore gas composition. Indications of methane oxidation were observed down to 2 m below ground in distances of more than 60 m from the landfill.

Effect of ozone depletion on atmospheric CH4 and CO concentrations

GLOBAL surface-based measurements of atmospheric methane and carbon monoxide concentrations revealed a marked and unex-pected decrease in their growth rates in 1991 and 1992, particularly in the Northern Hemisphere1,2. Changes in emissions are unlikely to be the sole reason for the sudden reduction in the concentrations of these source gases2,3. The unprecedentedly large depletion of stratospheric ozone observed in 1991 and 1992 (ref. 4) may have contributed to the sharp decrease in the growth rates of both CH4 and CO by exposing the troposphere to more ultraviolet radiation. This would have resulted in increased concentrations of the hydroxyl radical, OH·, which is the major atmospheric sink for both CH4 and CO. Here we present two-dimensional model simulations which allow us to assess the significance of the link between stra-tospheric ozone depletion and the observed trends of CH4 and CO. We find that the low values in stratospheric ozone concentration can account for almost half of the 1992 decrease in the CH4 and CO growth rates.

Differential absorption measurement of methane with two spatially resolved laser lines

Simultaneous and independent lasing on two different atomic lines is achieved with spatial resolution of laser eigenstates in conjunction with intracavity frequency selection. A sensitivity of 0.3 part in 10(6) meter in the differential detection of methane in 1 atm of air is experimentally demonstrated with this novel dual-wavelength laser. Monitoring the output intensities of the two orthogonally polarized eigenstates permits absolute measurement of methane concentration.

Methane oxidation associated with mid-depth methane maxima in the Southern California Bight

Methane concentration in the water column of the Southern California Bight exhibits two or more maxima. In the upper water column, a subsurface concentration maximum is often observed, usually near the bottom of the euphotic zone. Deeper maxima are often detected, well below the euphotic zone and separated from the sediments, which suggests an advective source from continental slope sediments. We measured methane concentrations and oxidation rates in an attempt to quantify the biological loss term for methane throughout the water column in the Santa Monica Basin, one of the semi-enclosed basins in the Southern California Borderland. The study site was in the central basin at a water depth of 900 m, which was sampled several times over 4 years, and an offshore transect of three stations, which was sampled once. Layers of methane rich water were detected in the mid water column (500–800 m depth) at the deeper stations, with concentrations exceeding those found in the subsurface maximum. Oxidation rates in these layers greatly exceeded rates associated with the subsurface maximum and represented turnover times on the order of a few months. The source of the methane at mid-depth is probably advection from petroliferous sediments in the margin of the borderland, rather than diffusion from underlying anoxic sediments in the basin. Relatively rapid oxidation rates and resulting turnover rates at depth imply the presence of a community adapted for the utilization of methane as a carbon source, a community which is not found in surface waters.

Rapid descent of mesospheric air into the stratospheric polar vortex

Wind fields from a numerical simulation are used to give a detailed Lagrangian picture of air flow in the middle atmosphere of the southern hemisphere in winter and early spring 1991. Trajectories for many thousands of air particles exhibit rapid descent of mesospheric air into the stratospheric polar vortex, revealing its organizing and structure‐preserving properties. Results are used to account for measurements of low methane concentrations in the vortex made by the HALOE instrument on board the Upper Atmosphere Research Satellite.

Soil texture parameterization of the methane uptake in aerated soils

Long-term records of the methane uptake by five different aerated soils in South-West Germany and spot measurements in Western Europe, North America, and North-West Africa are presented. A good correlation between the methane uptake rate and soil permeability, obtained from parallel 222Radon flux and concentration measurements of methane and 222Radon in soil air indicates, that methane consumption in aerated soils is mainly controlled by the gas transport resistance within the soil. Soil temperature is found to be of minor influence on the methane flux from the atmosphere into the soil. The soils investigated were classified with respect to the three major soil texture classes - coarse, medium, and fine - representing soils with low, medium, and high gas transport resistance, respectively. Average methane uptake rates for each soil texture class were determined and extrapolated to fit into the scheme of the NASA-GISS global digital data set of soil types (Staub et al., 1987). Assuming that the observed relation between methane uptake rate and soil permeability (soil texture) is valid for all kinds of aerated soils, methane uptake rates are estimated on a regional and global scale. From this parameterization we calculate a global CH 4 soil sink in the range of 9.0 to 55.9 Tg CH 4/a with a best estimate of 28.7 Tg CH 4/a. This corresponds to about 7% of the total global destruction rate by OH radicals.

The regional budget of atmospheric methane of a highly populated area

A regional methane budget for the catchment area of Heidelberg has been established, using quasi-continuous measurements of the atmospheric methane concentration and its stable isotope ratios ( 13 C 12 C , D/H). Methane in Heidelberg shows a mean concentration offset of 155 ppbv relative to background air. This concentration offset is due to a direct influence from - mainly anthropogenic - continental European methane sources. Using parallel atmospheric 222Radon observations, and the observed CH 4 concentration offset, we estimated the mean CH 4 flux density within the catchment area to be (12±6) gCH 4 m −2 yr −1. This is three times the global average for continental surfaces. From the stable isotope observations we derived the isotopic composition of the mean methane source to be δ 13 C source ( PDB) = (−54.3±1.7)‰ and δ D source ( SMOW) = (−270±41)‰ . In an independent approach we evaluated the distribution of methane sources from source statistics within a catchment area of ca. 500 km radius around Heidelberg. With help of a simple dispersion model we then calculated their contributions to the concentration offset at the sampling site. Using the isotopic composition of the mean source as constraint to adjust the specific emissions of individual sources it turned out that the major contributions to the observed concentration offset in Heidelberg are from cattle (37%), landfills (27%), coal mining (12%), agricultural wastes (11%), burning of fuels (8%), and gas leakages (5%). This source mix is more or less the same as in the whole catchment area (e.g. Central Europe).

Flame behavior at the combustion-chamber corner of a spark ignition engine. 1st report. Combustion-bomb experiments without blowby gas flow.

This paper describes the effects of a combustion-chamber corner on flame propagation into the ring crevice of a spark ignition engine. Because hydrocarbons from the engine can be reduced by flame propagation into the crevice, it is necessary to reveal flame behavior at the corner which dominates the flame propagation. We have conducted optical experiments of the flame propagation process toward the corner by the schlieren photography method. we have, furthermore, measured methane concentration at the corner and also at the side wall to calculate quenching distances. We have concluded the effect of the corner is greater than that of the side wall under a lean condition, based on the fact that the corner is about four times larger than the side wall in quenching distance when the equivalence ratio is 0.60.

Methane oxidation in Saanich inlet during summer stratification

Saanich Inlet, British Columbia, a fjord on the southeast coast of Vancouver Island, typically stratifies in summer, leading to the formation of an oxic-anoxic interface in the water column and accumulation of methane in the deep water. We present the results of methane concentration measurements in the water column of the inlet at various times throughout the summer months in 1983. Methane gradients and calculated diffusive fluxes across the oxic-anoxic interface increased as the summer progressed. Methane distribution and consumption in Saanich Inlet were studied in more detail during August 1986. At this time, a typical summer stratification with an oxic-anoxic interface around 140 m was present. At the interface, steep gradients in nutrient concentrations, bacterial abundance and methane concentration were observed. Methane oxidation was detected in the aerobic surface waters and in the anaerobic deep layer, but highest rates occurred in a narrow layer at the oxic-anoxic interface. Estimated methane oxidation rates were sufficient to consume 100% of the methane provided by diffusive flux from the anoxic layer. Methane oxidation is thus a mechanism whereby atmospheric flux from anoxic waters is minimized.

Tropospheric methane: Concentrations between 1963 and 1970

Previously unpublished measurements of methane concentrations in surface air (1963 to 1970) are reported. The values obtained, which ranged from 1.37 to 1.57 ppm by volume (moles), are consistent with current literature reports of 1.68 ppm in mid‐1982 and an annual increase of just over 1%.

Tropospheric methane in the mid-latitudes of the Southern Hemisphere

Results of more than 800 new measurements of methane (CH4) concentrations in the Southern Hemisphere troposphere (34–41° S, 130–150° E) are reported. These were obtained between September 1980 and March 1983 from the surface at Cape Grim, Tasmania, through the middle (3.5–5.5 km) to the upper troposphere (7–10 km). The concentration of CH4 increased throughout the entire troposphere over the measurement period, adding further support to the view that CH4 concentrations are currently increasing on a global scale. For data averaged vertically through the troposphere the rate of increase found was 20 ppbv/yr or 1.3%/yr at December 1981. In the surface CH4 data a seasonal cycle with a peak to peak amplitude of approximately 28 ppbv is seen, with the minimum concentration occurring in March and the maximum in September–October. A cycle with the same phase as that seen at the surface, but with a significantly decreased amplitude, is apparent in the mid troposphere but no cycle is detected in the upper tropospheric data. The phase and amplitude of the cycle are qualitatively in agreement with the concept that the major sink for methane is oxidation by hydroxyl radicals. Also presented is evidence of a positive vertical gradient in methane, with a suggestion that the magnitude of this gradient has changed over the period of measurements.

Analysis of ancient atmospheres

In 1967 and 1968, ice samples were taken from various depths in the ice caps of Greenland and Antarctica and transported to the Stanford Research Institute laboratories in the frozen state. These samples ranged in age from 100 to 2500 years. After the ice samples had been melted in the laboratory, the air trapped as compressed bubbles in the glacial ice during the transition from firn to ice was collected and removed by a novel technique developed for this specific purpose. Carbon monoxide and methane analyses were made on a large number of samples by using gas chromatography. Major components were also measured in a few samples by mass spectrometry. The measured methane concentration appear to be about half of present-day concentrations. The measured CO concentrations were high in value by severalfold, and initially the validity of the approach was doubted. However, in the light of recent evidence suggesting that the largest global source of CO is oxidized methane, our CO and CH4 measurements can be reinterpreted. They suggest that the background CO concentration in the atmosphere has been near current concentrations of about 0.1 ppm for many centuries. It can be inferred, therefore, that no large increase in CO concentration accompanied the advent of the Industrial Revolution.

Materialprüfung

A compact system for methane sensing based on the Quartz-Enhanced Photoacoustic Spectroscopy technique has been developed. This development has been taken through two versions which were based respectively on a Fabry Perot quantum wells diode laser emitting at 2.3 μm, and on a quantum wells distributed feedback diode laser emitting at 3.26 μm. These lasers emit near room temperature in the continuous wave regime. A spectrophone consisting of a quartz tuning fork and one steel microresonator was used. Second derivative wavelength modulation detection was used to perform low methane concentration measurements. The sensitivity and the linearity of the QEPAS sensor were studied. A normalized noise equivalent absorption coefficient of 7.26 × 10−6 cm−1 W/Hz1/2 was achieved. This corresponds to a detection limit of 15 ppmv for 12 s acquisition time.

Methane in the atmosphere.

Methane is present in the troposphere with a volume concentration of about 1.5 ppm. Estimates of Koyama indicate a predominantly biological origin with a total production rate of about 2.7 x 10/sup 14/ g CH/sub 4//yr. From that the author estimated the atmospheric lifetime of methane to be around 20 years. Measurements of the C-14 in methane by Libby and later by Bainbridge, et al. gave a C-14 content of 75% of recent wood and, therefore, confirm the predominant biological origin, the addition of inactive CH; from industrial sources being only about 25%. Much less is known about sinks of CH/sub 4/. Cadle reported fairly high destruction rates by atomic O, a reaction which should be important at high altitude. Bainbridge reports a decrease in the measured methane concentration above the tropopause. He, however, considers this decrease too small to account for the destruction rate of 20 years estimated by Koyama. Measurements on air samples collected on aircraft flights at various altitudes show a high variability of the CH/sub 4/ content both with time and altitude.