CH4 Values Research Articles

The stable carbon isotope signature of methane produced by saprotrophic fungi

Abstract. Methane (CH4) is the most abundant organic compound in the atmosphere and is emitted from many biotic and abiotic sources. Recent studies have shown that CH4 production occurs under aerobic conditions in eukaryotes, such as plants, animals, algae, and saprotrophic fungi. Saprotrophic fungi play an important role in nutrient recycling in terrestrial ecosystems via the decomposition of plant litter. Although CH4 production by saprotrophic fungi has been reported, no data on the stable carbon isotope values of the emitted CH4 (δ13C-CH4 values) are currently available. In this study, we measured the δ13C values of CH4 and carbon dioxide (δ13C-CO2 values) emitted by two saprotrophic fungi, Pleurotus sapidus (oyster mushroom) and Laetiporus sulphureus (sulphur shelf), cultivated on three different substrates, pine wood (Pinus sylvestris), grass (mixture of Lolium perenne, Poa pratensis, and Festuca rubra), and corn (Zea mays), which reflect both C3 and C4 plants with distinguished bulk δ13C values. Applying Keeling plots, we found that the δ13C source values of CH4 emitted from fungi cover a wide range from −40 to −69 mUr depending on the growth substrate and fungal species. Whilst little apparent carbon isotopic fractionation (in the range from −0.3 to 4.6 mUr) was calculated for the δ13C values of CO2 released from P. sapidus and L. sulphureus relative to the bulk δ13C values of the growth substrates, much larger carbon isotopic fractionations (ranging from −22 to −42 mUr) were observed for the formation of CH4. Although the two fungal species showed similar δ13CH4 source values when grown on pine wood, δ13CH4 source values differed substantially between the two fungal species when they were grown on grass or corn. We found that the source values of δ13CH4 emitted by saprotrophic fungi are highly dependent on the fungal species and the metabolized substrate. The source values of δ13CH4 cover a broad range and overlap with values reported for methanogenic archaea, the thermogenic degradation of organic matter, and other eukaryotes.

A gasket-type standard leak element using femtosecond laser micromachining

A gasket-type standard leak element with a microfluidic channel was developed and measured. The microfluidic channel with a diameter of several micrometers and a length of one hundred micrometers was fabricated by using femtosecond laser micromachining. The conductances (<1 × 10−6 L s−1) of the microfluidic channel for various non-condensable gases -- H2, He, CH4, N2 and CO2 were determined by a measuring system based on conductance modulation (CM) method. The experimental results show that the flow characteristics of our devices exhibit molecular flow at a pressure up to 100 mbar and the conductance values of H2, He, CH4, N2 and CO2 are inversely proportional to the square root of their molecular mass.

Effects of warming on carbon emission and microbial abundances across different soil depths of a peatland in the permafrost region under anaerobic condition

Peatlands in permafrost region are large carbon pools sensitive to global warming. However, the effects of increased temperature on carbon emissions and associated microbial abundances of peatlands under anaerobic condition remain largely unknown, especially when considering depths. For supplementing the deficiency about this, we collected soil from 0 to 150 cm depth of a permafrost peatland in the Great Hing'an Mountain and incubated at 5 and 15 °C for 55 days under anaerobic condition. Soil CO2 and CH4 emissions were detected during incubation, and inorganic nitrogen, dissolved organic carbon, and carbon-cycling microbial abundances were analyzed at the end of incubation. Results showed that emission rates and cumulative emissions amount of CO2 and CH4 at 15 °C across all soil depths were higher than those observed at 5 °C. Specifically, 0–20 cm and 20–40 cm layers had the highest CO2 emission rates and cumulative emission amounts, whereas the 40–60 cm and 60–80 cm layers had the highest CH4 emission rates and cumulative emission amounts. Mean temperature sensitivity (Q10) values of CO2 and CH4 were 2.39 and 55.49 respectively. Q10 values of bacteria, fungi, archaea, methanogen, and methanotroph abundances were 1.17, 3.85, 1.75, 1.68, and 1.66 respectively, which were calculated by the abundance ratio of microbial functional gene at 15 °C and 5 °C. Similar to the trend of CO2 emissions, high bacteria, fungi, archaea, methanogen, and methanotroph functional gene abundances were also observed in 0–20 cm and 20–40 cm layers, and such abundances increased along with temperature increasing. In sum, elevated temperature enhances the carbon emission of peatland in permafrost region, and the warming simulated CO2 emission is linked to the abundances of carbon-cycling microorganisms.

A New Background Method for Greenhouse Gases Flux Calculation Based in Back-Trajectories Over the Amazon

The large amount of carbon stored in trees and soils of the Amazon rain forest is under pressure from land use as well as climate change. Therefore, various efforts to monitor greenhouse gas exchange between the Amazon forest and the atmosphere are now ongoing, including regular vertical profile (surface to 4.5 km) greenhouse gas measurements across the Amazon. These profile measurements can be used to calculate fluxes to and from the rain forest to the atmosphere at large spatial scales by considering the enhancement or depletion relative to the mole fraction of air entering the Amazon basin from the Atlantic, providing an important diagnostic of the state, changes and sensitivities of the forests. Previous studies have estimated greenhouse gas mole fractions of incoming air (‘background’) as a weighted mean of mole fractions measured at two background sites, Barbados (Northern Hemisphere) and Ascension (Southern hemisphere) in the Tropical Atlantic, where the weights were based on sulphur hexafluoride (SF6) measured locally (in the Amazon vertical profiles) and at the two background sites. However, this method requires the accuracy and precision of SF6 measurements to be significantly better than 0.1 parts per trillion (picomole mole−1), which is near the limit for the best SF6 measurements and assumes that there are no SF6 sources in the Amazon basin. We therefore present here an alternative method. Instead of using SF6, we use the geographical position of each air-mass back-trajectory when it intersects the limit connecting these two sites to estimate contributions from Barbados versus Ascension. We furthermore extend the approach to include an observation site further south, Cape Point, South Africa. We evaluate our method using CO2 vertical profile measurements at a coastal site in Brazil comparing with values obtained using this method where we find a high correlation (r2 = 0.77). Similarly, we obtain good agreement for CO2 background when comparing our results with those based on SF6, for the period 2010–2011 when the SF6 measurements had excellent precision and accuracy. We also found high correspondence between the methods for background values of CO, N2O and CH4. Finally, flux estimates based on our new method agree well with the CO2 flux estimates for 2010 and 2011 estimated using the SF6-based method. Together, our findings suggest that our trajectory-based method is a robust new way to derive background air concentrations for the purpose of greenhouse gas flux estimation using vertical profile data.

Methane Emissions and Milk Fatty Acid Profiles in Dairy Cows Fed Linseed, Measured at the Group Level in a Naturally Ventilated Housing and Individually in Respiration Chambers.

Simple SummaryCows emit the greenhouse gas methane (CH4) as a result of microbial feed digestion. Methane emissions can be reduced by adopting nutritional strategies, such as dietary supplementation of linseed. Additionally, the oil in linseed increases the proportion of favorable fatty acids in milk fat. This study evaluated the effect of linseed on CH4 emission and milk fatty acid composition measured in a group of cows in a naturally ventilated barn and in individual cows in respiration chambers. The substantially higher proportions of favorable fatty acids in the milk of linseed-fed cows were detected in individual milk samples and in the milk of the herd. Therefore, the analysis of bulk milk could be a suitable control instrument for retailers. Visualizing the course of CH4 emissions over a whole day showed slightly lower CH4 values in linseed-supplemented individuals and groups. However, we found no significant reduction of CH4 as a result of linseed supplementation. Feed supplements in concentrations that are effective in reducing CH4 must show whether the reduction potential is comparable when determined at the group and individual levels. The present study evaluated the effects of linseed supplementation on CH4 emission and milk fatty acid composition in dairy cows measured at the group level in an experimental dairy loose housing using a tracer gas technique and individually in tied stalls and respiration chambers. Cows (2 × 20) were maintained in two separate sections under loose-housing conditions and received a diet supplemented with extruded linseed (L) lipids (29 g·kg−1 dry matter) or a control (C) diet containing corn flour. Subsequently, 2 × 6 cows per dietary group were investigated in a tied-housing system and respiration chambers. Substantially higher proportions of favorable milk fatty acids were recovered in L cows when compared with C cows at the group level, making the analysis of bulk milk a suitable control instrument for retailers. Linseed supplementation resulted in a slightly lower diurnal course of CH4 emission intensity than the control at the group and individual levels. However, we found no more than a trend for a CH4 mitigating effect, unlike in other studies supplementing similar linseed lipid levels. Feed supplements in concentrations that lead to a significant reduction in CH4 emissions must show whether the reduction potential determined at the group and individual levels is comparable.

Greenhouse gas emissions from advanced nitrogen-removal onsite wastewater treatment systems

Advanced onsite wastewater treatment systems (OWTS) designed to remove nitrogen from residential wastewater play an important role in protecting environmental and public health. Nevertheless, the microbial processes involved in treatment produce greenhouse gases (GHGs) that contribute to global climate change, including CO2, CH4, N2O. We measured GHG emissions from 27 advanced N-removal OWTS in the towns of Jamestown and Charlestown, Rhode Island, USA, and assessed differences in flux based on OWTS technology, home occupancy (year-round vs. seasonal), and zone within the system (oxic vs. anoxic/hypoxic). We also investigated the relationship between flux and wastewater properties. Flux values for CO2, CH4, and N2O ranged from −0.44 to 61.8, −0.0029 to 25.3, and −0.02 to 0.23 μmol GHG m−2 s−1, respectively. CO2 and N2O flux varied among technologies, whereas occupancy pattern did not significantly impact any GHG fluxes. CO2 and CH4 – but not N2O – flux was significantly higher in the anoxic/hypoxic zone than in the oxic zone. Greenhouse gas fluxes in the oxic zone were not related to any wastewater properties. CO2 and CH4 flux from the anoxic/hypoxic zone peaked at ~22-23 °C, and was negatively correlated with dissolved oxygen levels, the latter suggesting that CO2 and CH4 flux result primarily from anaerobic respiration. Ammonium concentration and CH4 flux were positively correlated, likely due to inhibition of CH4 oxidation by NH4+. N2O flux in the anoxic/hypoxic zone was not correlated to any wastewater property. We estimate that advanced N-removal OWTS contribute 262 g CO2 equivalents capita−1 day−1, slightly lower than emissions from conventional OWTS. Our results suggest that technology influences CO2 and N2O flux and zone influences CO2 and CH4 flux, while occupancy pattern does not appear to impact GHG flux. Manipulating wastewater properties, such as temperature and dissolved oxygen, may help mitigate GHG emissions from these systems.

Irritable bowel syndrome and small intestinal bacterial overgrowth: Assessment with breath test

Background: Irritable bowel syndrome (IBS) has been considered a functional disease, however evidences suggest organic abnormalities as disbiosis. The aim of this study was to evaluate bacterial overgrowth syndrome in IBS patients. Methods: Patients with IBS were submited to the expired H2 and CH4 breath test, with analyzes of exhaled air in fasting (zero minutes) and after the administration of 10g of lactulose, at times: 15, 30, 60, 90, 120, 150 and 180 minutes. The test was considered positive when the values of H2 or CH4 at 90 minutes were 20 ppm above baseline values. Results: Fourth-six patients were included, 23 (50%) had diarrheal subtype, 12 (26.1%) had constipated subtype and 11 (23.9%) had mixed subtype. All patients were submitted to lactulose breath test (LBT), with evaluation of expired H2 and CH4. The H2 test positivity was 15.2% and the CH4 test was 10.9%. In the diarrheal subgroup, the positivity of the H2 test was 13%, and at the CH4 test was 8.7%. Among the constipated patients, 16.7% were positive for H2 test, and none was positive for CH4 test. At the mixed subtype, the H2 test was positive for 18.2% and CH4 test for 27.3%. There was no significant correlation between the positivity of expired H2 test with the diarrheal subtype, and neither the expired CH4 test with the constipated subtype. Conclusion: LBT has not altered in patients with three forms of IBS. The optimization of diagnostic methods is necessary for a more accurate diagnosis.

Spatial and temporal heterogeneity of geochemical controls on carbon cycling in a tidal salt marsh

Tidal salt marsh ecosystems store copious amounts of carbon (C) within sediments. In order to predict how these C stores may be affected by environmental change, it is critical to assess current CO2 and CH4 production and efflux from these ecosystems. Production and efflux of these greenhouse gases (GHGs) are governed by coupled geochemical, hydrological, physical and biological processes in sediments that are sensitive to local conditions, which can result in large spatial and temporal heterogeneity of GHGs dynamics within the ecosystem. To understand how the drivers of GHGs dynamics vary across salt marsh ecosystems, we coupled solid-phase geochemistry to measurements of porewater chemistry (to ∼1 m), CO2 and CH4 production in sediments and efflux to the atmosphere in a temperate tidal salt marsh for over one year to capture seasonal patterns within two vegetation zones of the marsh landscape that have distinct biogeochemical and hydrologic conditions: Tall Spartina (TS) and Short Spartina (SS). The SS vegetation zone experienced nearly constant inundation, low redox values (−200 to 200 mV), porewater pH 6–7 that did not vary with depth or time, an enrichment of pyrite and goethite with depth and up to 3 mM porewater sulfide. In contrast, the TS vegetation zone on the natural levee proximal to a tidal channel experienced large water level oscillations due to spring-neap tides that resulted in variable but higher redox values (0–700 mV), porewater pH 6–7 at depth but surface (0–3 cm) as low as 4 in the spring, an enrichment of ferrihydrite and a depletion of pyrite at ∼30 cm, and up to 0.8 mM ferrous Fe in porewater. At 50–56 cm, solid phase analyses (STXM-NEXAFS) revealed differential C speciation between the two vegetation zones, with stronger C-Fe spatial association at TS and stronger C-Ca co-association at SS despite both having similar soil pH of 3–4. These results suggest that soil pH may not be strongly predictive of C-mineral control in flooded marsh sediments. Both vegetation zones showed consistent CO2 and CH4 emissions from sediments to the atmosphere throughout the study period with TS having ∼60% higher median CO2 and SS having ∼55% higher median CH4 efflux. Using depth profiling, unexpectedly high concentrations of CO2 (>200 μM) and CH4 (>200 μM) were observed at depths 50–75 cm at both zones that were higher for SS in these sulfate-rich (up to 17 mM) sediments, which suggests methylotrophic methanogenesis occurs deep within the profile of salt marsh sediments away from the tidal channel. Moreover, if we extrapolate our median depth values of CH4 and CO2 to the 5.3 Mha of global salt marshes, this could account for a conservative estimate of ∼70 Gg of unaccounted C stored in gaseous form (i.e., CH4 and CO2) in marsh sediments, which should be considered when attempting to understand the current patterns and future responses of carbon dynamics from these ecosystems.

Effect of shale properties on CH4 and CO2 sorption capacity in Czech Silurian shales

The study involved an experimental assessment of the CO2 and CH4 sorption capacity of seven dark Silurian shale samples from three formations in the Barrandian Basin (Czech Republic). The shale samples had dominant inorganic matter consisting mainly of clay minerals, quartz, calcite and plagioclase, and very low organic matter. Most of the organic particles were the remains of zooclasts, especially graptolites and bitumens. The graptolite reflectance (Rr) reflecting the degree of thermal maturation of the shales ranges between 0.56% in the Kopanina Formation and 1.09% in the Litohlavy Formation, with the exception of the probably thermally altered part of the Motol Formation, which has reflectance higher than 1.70%. The total organic carbon (TOC) content was found to be in the range of 0.34–2.37 wt%. The porosity values were from 4.6% to 18.8%. In all shale samples, the high pressure excess sorption isotherms of CO2 and CH4 were measured at a temperature of 45 °C for both gases at pressures up to 8 MPa for CO2 and up to 15 MPa for CH4 on dry samples, using a manometric sorption apparatus. The Gibbs equation was used for evaluation of the maximum excess sorption (nmax,CO2 and nmax,CH4). The nmax,CO2 values ranged from 0.118 mmol/g to 0.244 mmol/g, while the nmax,CH4 values were more than twice lower (0.050 mmol/g - 0.088 mmol/g). The xCO2/CH4 ratio ranged from 1.47 to 2.98, with a median value of 2.54, calculated without the sample from the Kopanina Formation (4.36). The influence of the shale parameters on the CO2 and CH4 sorption capacity was determined. No relation has been proven between the value of Rr and the TOC-normalized CO2 and CH4 sorption capacities. The CO2 sorption capacity showed a negative correlation with TOC and with clay minerals but a positive correlation with quartz, while the behaviour of CH4 was opposite in these cases. A strong positive correlation was found between the volume of micropores and the CO2 excess sorption capacity, and negative dependence was found for CH4. The CO2 sorption capacities always depend on the micropores content, and the CH4 capacities depend on the shale components.

Residual gas in extensive stratified Miocene Izura carbonate concretions exhibiting thermogenic origin and isotopic fractionation associated with carbonate precipitation

A major carbonate-cemented strata and carbonate concretions intercalated in the Early Miocene Kokozura Formation are common in the Izura area along the Pacific coast, in north Ibaraki, Japan. Chemotrophic mollusk fossils occur frequently with the Izura carbonate concretions. Significant quantities of archaeal biomarkers such as pentamethylicosane, crocetane, and squalane are detected in the carbonate concretions. Residual gas from pulverizing the carbonate concretion contains mostly CO2 with subordinate amounts of CH4, C2H6, and C3H8. The CH4/(C2H6+C3H8) ratio and the δ13C values of CH4 and carbonate indicate the Izura carbonate concretions originate from thermogenic methane. The extent of isotopic fractionation during formation of the carbonate concretions is determined by a novel dataset of δ13C values of CO2 in the residual gas and carbonates. Largescale leakage of thermogenic methane due to the deformation, fissuring, and destruction of the paleo-Izura petroleum deposit produced the vast Izura carbonate concretions. This deformation is associated with the tectonic separation of Japanese Islands from the paleo-Eurasian continent in the late Early Miocene.

Impact of iron release by volcanic ash alteration on carbon cycling in sediments of the northern Hikurangi margin

We present geochemical data collected from volcanic ash-bearing sediments on the upper slope of the northern Hikurangi margin during the RV SONNE SO247 expedition in 2016. Gravity coring and seafloor drilling with the MARUM-MeBo200 allowed for collection of sediments down to 105 meters below seafloor (mbsf). Release of dissolved Sr2+ with isotopic composition enriched in 86Sr (87Sr/86Sr minimum = 0.708461 at 83.5 mbsf) is indicative of ash alteration. This reaction releases other cations in the 30-70 mbsf depth interval as reflected by maxima in pore-water Ca2+ and Ba2+ concentrations. In addition, we posit that Fe(III) in volcanogenic glass serves as an electron acceptor for methane oxidation, a reaction that releases Fe2+ measured in the pore fluids to a maximum concentration of 184 μM. Several lines of evidence support our proposed coupling of ash alteration with Fe-mediated anaerobic oxidation of methane (Fe-AOM) beneath the sulfate-methane transition (SMT), which lies at ∼7 mbsf at this site. In the ∼30-70 mbsf interval, we observe a concurrent increase in Fe2+ and a depletion of CH4 with a well-defined decrease in δ13C-CH4 values indicative of microbial fractionation of carbon. The negative excursions in δ13C values of both DIC and CH4 are similar to that observed by sulfate-driven AOM at low SO42− concentrations, and can only be explained by the microbially-mediated carbon isotope equilibration between CH4 and DIC. Mass balance considerations reveal that the iron cycled through the coupled ash alteration and AOM reactions is consumed as authigenic Fe-bearing minerals. This iron sink term derived from the mass balance is consistent with the amount of iron present as carbonate minerals, as estimated from sequential extraction analyses. Using a numerical modeling approach we estimate the rate of Fe-AOM to be on the order of 0.4 μmol cm−2 yr−1, which accounts for ∼12% of total CH4 removal in the sediments. Although not without uncertainties, the results presented reveal that Fe-AOM in ash-bearing sediments is significantly lower than the sulfate-driven CH4 consumption, which at this site is 3.0 μmol cm−2 yr−1. We highlight that Fe(III) in ash can potentially serve as an electron acceptor for methane oxidation in sulfate-depleted settings. This is relevant to our understanding of C-Fe cycling in the methanic zone that typically underlies the SMT and could be important in supporting the deep biosphere.

Thermodynamics analysis of the adsorption of CH4 and CO2 on montmorillonite

The greater adsorption ability of shale to CO2 offers an alternative method to enhance shale gas recovery, where a potential solution for CO2 sequestration into a deep shale reservoir can also be realized. Clay minerals are the important storage space for shale gas. In this work, the isotherm adsorption curves of CH4 and CO2 on montmorillonite at 288 K, 308 K and 328 K were obtained using gravimetric apparatus. The selectivity factor of CO2 over CH4 (SCO2/CH4) and Henry's constants (KH) of CH4 and CO2 were calculated. More importantly, the thermodynamics parameters of CH4 and CO2, including Gibbs free energy change (ΔG), surface potential (Ω), isosteric heat of adsorption (Qst) and entropy change (ΔS), were thoroughly analysed. The results indicate that all SCO2/CH4 values are obviously greater than one, and injecting CO2 into a clay-rich shale reservoir to enhance the shale gas recovery is feasible. CH4 has smaller KH than CO2, which shows that CH4 has a weaker affinity on the montmorillonite surface. Low temperature helps to enlarge KH and promote the adsorption of CH4 and CO2. Increasing the pressure causes the increase in ΔG and Ω of CH4 and CO2. The higher ΔG and Ω of CO2 compared to CH4 reveal that the CO2 adsorption on montmorillonite is more favourable and spontaneous. When the loading increases, the Qst values of CH4 and CO2 reduce. CH4 has a smaller Qst than CO2, which suggests the stronger interaction of CO2 with montmorillonite. CH4 and CO2 have decreasing ΔS with the loading. Under larger surface coverage conditions, the disorder of the adsorbed molecules is larger, and most of the injected molecules are trapped as a free state in the pore space. The higher ΔS of CO2 illustrates that CO2 molecules constitute a much more stable rearrangement than CH4 molecules. The temperature has a slight effect on the ΔS of CH4 and CO2.

Response of methane emissions to litter input manipulation in a temperate freshwater marsh, Northeast China

The photograph of the field experiment of different litter input manipulations in situ and the treatment effects on CH 4 fluxes during observations in 2015 and 2016. Abbreviations: NL, no aboveground litter; DL, double litter; CK, control; AR, standing litter removal. • We conducted a two seasons litter input manipulation experiment in a freshwater marsh. • Litter input manipulations obviously affected CH 4 emission and surface DOC contents. • Litter removal induced higher soil temperature, DOC content and CH 4 emission. • The abundance of methanogens in surface soil relied on the ways of litter manipulation. Plant litter plays an important role in regulating CH 4 emission in wetland ecosystems. Our knowledge of the impacts of plant litter on CH 4 budget is important for understanding the response and feedbacks of wetland ecosystems to climate warming. Nevertheless, the effects of plant litter on CH 4 emission and temperature sensitivity (Q 10 ) are not clear under the background of global change. In this study, a field litter inputs manipulation experiment with four treatments including no aboveground litter (NL), standing litter removal (AR), doubled litter input (DL) and controls (CK) was conducted to study the effects of litter manipulations on CH 4 emission in a seasonal inundated freshwater marsh over two growing seasons of 2015 and 2016 in the Sanjiang Plain, Northeast China. Results showed that CH 4 emission was significantly associated with altered litter input over the observation period. Compared with CK, the cumulative CH 4 emission increased by 105.83%, 42.20% and 42.50% for NL, AR and DL treatments, respectively, in 2015, and the values were 199.04%, 115.55% and 17.55%, in 2016. Variances of CH 4 emission were more sensitive to litter removal effects. Altered litter input also significantly affected the dissolved organic carbon (DOC) concentration ([DOC]) in surface pore water. DL and CK treatments with lower soil temperature had lower [DOC] than litter removal treatments of NL and AR. The abundance of methanogens among the four treatments exhibited synchronous change with DOC over the observation period. The Q 10 values of CH 4 emission didn’t show consistent changing patterns with those of DOC among different litter input treatments, which was probably due to the different temperature sensitivity of dominant methanogen types. Due to its great effects on soil microclimate, substrate availability and the concomitant variation in temperature sensitivity, our results highlighted that plant litter effects should be incorporated into the current process-based CH 4 biogeochemical models to predict future CH 4 fluxes from natural wetlands under the background of global change.

Variations of methane in the Antarctic atmosphere in 2009–2017 by ground-based and satellite data

The article presents the results of systematic measurements (2009−2017) of the total column abundances of methane (TC_CH4 ) and the column-averaged concentration (X_CH4 ) at the Antarctic station Novolazarevskaya. Solar radiation is recorded in the range 2990 – 3006 cm–1 using a diffraction spectrometer with 0.2 cm–1 resolution. The inverse task CH4 total column determining is achieved using the SFIT4 v0.9.4.4 code. The analysis shows that during the measurement period the average TC_CH4 was (3.4±0.8).1019 molecules/cm2 during the measurement period, and the average X_CH4 is (1663±34) ppbv. TC_CH4 trend is (4.5±2.2).1015 molecules/cm2 /month, and X_CH4 trend is (0.28 ± 0.11) ppbv/month. The average TC_CH4 values and trend at Novolazarevskaya are in good agreement with the measurements by the Brucker120HR instrument at the Arrival Heights station. Seasonal variations of atmospheric methane have the maximum in October–November and the minimum in May–July. The trends of surface methane concentrations at Sywa, the Halley station and the Amundsen-Scott South Pole station are 0.59 – 0.61 ppbv/month and exceed the trend of the column-averaged concentration at Novolazarevskaya and AIRS trends for the troposphere (0.24 – 0.32) ppbv/month, due to a decrease in the maximal values of TC_CH4 in the period after 2014. The closest agreement of X_CH4 variations at Novolazarevskaya with AIRS data is observed at the levels of 150–200 hPa. Significant semiannual harmonics varied with height are characteristic of CH4 variations according to the AIRS data. The interference of annual and semiannual harmonics leads to the appearance of two maxima in the seasonal variations of methane with relative position to each other varies with height. The statistical model is developed for all the series considered. It approximates the trend, annual and semi-annual components of CH4 oscillations.The authors have no competing interests.

Experimental and principal component analysis studies on minimum oxygen concentration of methane explosion

Gas explosion has always been one of the leading disasters in chemical and mining industries, causing tremendous considerable casualties and property damage. It is very effective to control ignition parameters to prevent explosion accidents. To intensively investigate the impacts of C2H6/C2H4/CO/H2 mixtures on CH4 explosion, we added C2H6/C2H4/CO/H2 mixtures with different ratios (samples 1–4) and different volume fractions ([mixture] = 0–2.0 vol%) to CH4/air([CH4] = 7.0, 9.5 and 11.0 vol%) for measurement of the flammability limit and minimum oxygen concentration (MOC) for CH4 explosion in a 20-L spherical vessel. Changes of flammability limits of CH4 were obtained with the addition of C2H6/C2H4/CO/H2 mixtures at room temperature (18–22 °C) and pressure (1 atm). The experimental data about MOC of CH4 explosion were examined by principal component analysis (PCA). On the basis of experimental results, multiple regression models were established to determine the influences of principal components on MOC of CH4 explosion. The results clearly indicated that the impacts of organic and inorganic combustible gases on flammability limits of CH4 were significantly different. The involvement of sample 1 and sample 2 (main component is organic flammable gas) increased the explosive hazard degree (F value) of CH4 by 43.18% and 45.45%, respectively. However, it was increased by 15.91% and 4.55%, respectively after adding sample 3 or sample 4 (main component is inorganic flammable gas). Additionally, the required MOC for CH4 explosion was increased with the increase of C2H6/C2H4/CO/H2 mixtures, and they showed a quadratic parabola relationship. Moreover, the linear expressions between the concentrations of C2H6, C2H4, CO and H2 and the MOC of CH4 explosion were achieved by PCA. Based on these analyses, it is indicated that the effects of C2H6, C2H4 and CO were increasingly significant on MOC while H2 was just the opposite from the oxygen-rich state to the stoichiometric state and fuel-rich state for CH4/air mixture. The results presented in this paper can provide theoretical reference for the prevention and control of multiple flammable gas explosion.

Methane dynamics in the coastal – Continental shelf transition zone of the Gulf of Cadiz

The concentration of CH4 in water was measured along five transects in the Gulf of Cadiz (Trafalgar, Sancti Petri, Guadalquivir, Tinto - Odiel and Guadiana) during four cruises throughout the months of March, June, September and December 2016. For two of the cruises water overlying three mud volcanoes situated in the Gulf of Cadiz were also sampled (San Petersburgo, 860 m; Pipoca, 460 m; and Anastasya, 500 m. In addition, the stable carbon isotopic compositions of dissolved CH4 (δ13C) were measured in the study area in June and December 2016. The mean CH4 value for the whole water column was 10.5 ± 4.3 nmol L−1, with large spatial and temporal variations. The highest values were found in June 2016 and the lowest in March 2016. In surface waters, the mean dissolved methane concentration was of 9.6 ± 2.6 nmol L−1. In most of the sampling area, high concentrations of CH4 were found in subsurface waters at depths close to the thermocline and at the coastal stations. The highest concentrations were obtained from the bottom waters above the Anastasya mud volcano (125 nmol L−1). The stable carbon isotope compositions ranged between - 29.2 and - 58.4‰, and the least negative values were associated with the highest CH4 concentrations in samples from above the mud volcanoes, related to thermogenic values. The sea-air fluxes of CH4 ranged from 12.4 to 37.7 μmol m−2 d−1, showing that the study area acts as a source of CH4 to the atmosphere.

Time-dependent observation of a cage-specific guest exchange in sI hydrates for CH4 recovery and CO2 sequestration

CH4–CO2 replacement in naturally occurring gas hydrates has been considered a promising method for both energy recovery and CO2 sequestration. In this study, the time-dependent guest exchange behaviors and guest distributions during CH4–CO2 replacement were closely examined at two different CO2 injecting pressures (2.2 and 3.5 MPa) using nuclear magnetic resonance (NMR), in-situ Raman spectroscopy, powder X-ray diffraction (PXRD), and gas chromatography. The 13C NMR spectra confirmed that the cage occupancy ratio of the CH4 molecules in the large 51262 and small 512 cages (θL/θS,CH4) after the replacement was significantly smaller than that before the replacement because of the preferential occupation of CO2 in the large 51262 cages. The time-dependent Raman spectra revealed that the rate of CO2 inclusion and the resultant CH4 depletion in the hydrate phase during the replacement was faster at a higher CO2 injecting pressure. The Rietveld refinement of the PXRD patterns offered a quantitative cage occupancy of CH4 and CO2 molecules before and after the replacement. The time-dependent cage occupancy values of CH4 and CO2 during the replacement obtained from a multi-methodological approach, which is a combination of PXRD analysis and in-situ Raman measurement, demonstrated that a significant guest exchange in the large 51262 cages had a greater effect on the extent of replacement and that the kinetics of the CH4–CO2 replacement was accelerated at a higher CO2 injecting pressure. The results provide a better understanding of the kinetics and mechanism of the cage-specific CH4–CO2 replacement occurring in the sI hydrates for CH4 recovery and CO2 sequestration.

Dry Reforming of Methane Using Cold Plasma; Kinetic Model Study

In this work, the dry reforming of methane was studied using a corona and gliding discharge plasma microreactors. A chemical kinetic model was developed to describe the experimental behavior observed. The kinetic model is proposed based on the assumption that the reactant molecules CH4 or CO2 are attacked by active species produced by the plasma discharges, and the production of this active species are a function of the plasma power. The modelization allowed the prediction of the conversion of the reactants (CH4 and CO2) according to the energy transfer to the gas (). The value is characteristic of the energy cost; the lower β value indicated better efficiency. The value of CH4 was found to be 10.42 and 58.25 J and for CO2 equal to 12.24 and 27.77 J for corona and gliding discharge plasma, respectively. The kinetic model also demonstrated that the methane and carbon dioxide conversion was an exponential function of the plasma energy, and were a linear function of the input energy for a CH4 and CO2 inlet concentration. Our Model also implied that a plasma reactor with a smaller input discharge power has better energy efficiency for CO2 andCH4 conversion.

Impact of biochar on greenhouse gas emissions from constructed wetlands under various influent chemical oxygen demand to nitrogen ratios

Biochar is widely used for nutrient removal in constructed wetlands (CWs); however, its influence on greenhouse gas (GHG) emissions from CWs remains unclear. Here, biochar was used to mitigate the global warming potential (GWP) from CWs and promote the removal of contaminants from simulated domestic wastewater under different influent chemical oxygen demand to nitrogen ratios (COD/N = 3, 6, 9, 12). Results demonstrated that biochar could improve the removal of COD, NH4+- N, and TN. The average N2O and CO2 fluxes were significantly lower and CH4 fluxes were higher in biochar-added CWs than those in none-biochar CWs. Biochar reduced GWP values of N2O and CH4 from 18.5% to 24.0%. N2O fluxes and GWP decreased, while CH4 and CO2 fluxes increased as COD/N ratios increased. Additionally, biochar increased the abundance of Geobacter and denitrifiers such as Hydrogenophaga. Overall, biochar could not only promote the removal of nutrients but also mitigate GWP in CWs.

PENGARUH PERBEDAAN BANTUK BAHAN BAKU DAN SUHU GASIFIKASI AMPAS TEBU TERHADAP PRODUKSI HIDROGEN

The use of fossil fuel at this time is very disturbing the survival, especially related to environmental and economic impacts. While the needs of world anergy continue to increase. The increase reached 80% until 2040. To overcome this problem, scientists have developed gasification technology that can produce fuel as a substitute for fossil fuel. Gasification from biomass can produce synthetic gas that is more environmentally friendly and renewable. so the purpose of this study was to determine the effect of different forms of raw material and temperature on hydrogen produced by the gasification process made from sugarcane bagasse. This research was conducted through a process of gasification made from bagasse biomass to produce synthetic gas that can replace fossil fuel. The type of reactor used is downdraft type reactor. This research was carried out by the gasification process using raw material in the form of sugarcane bagasse with diameters and lengths of 6 mm and 50 mm respectively and the others in the form of fibers . Gasification is also carried out with variations in temperature, namely 800, 950 and 1,050oC . After that, the synthetic gas produced is tested by Gas Chromatography on each variable so that the hydrogen content is known. The hydrogen produced is defined in the form of H2, CH4 products, and the value of hydrogen conversion efficiency. The results obtained showed an increase in H2, CH4, and hydrogen conversion efficiency with an increase in gasification temperature, both in the form of pellets and ash. As for the change in the form of raw materials from pellets to fibers, it causes a decrease in H2, CH4, and hydrogen conversion efficiency values. H2 compositions produced at temperatures of 800, 950, and 1050oC were 10.618, 12.080, 11.312% by volume and 3.025, 2.925, 3.150% by volume, respectively. CH4 composition for raw materials in the form of pellets and fibers at temperatures of 800, 950, and 1050oC were 1.040, 2.622, 2.867% by volume and 0.846, 0.856, 1.051% by volume, respectively. The value obtained is relatively very small compared to the results obtained in previous studies. The value of hydrogen conversion efficiency for raw materials in the form of pellets and fibers at 800, 950, and 1050oC are 1.62%, 3.45%, 3.91% and 1.89%, 1.92%, 2, 32%.