Articoli di riviste: "Atmospheric methane"

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Jensen, Sigmund, Anders Priemé e Lars Bakken. "Methanol Improves Methane Uptake in Starved Methanotrophic Microorganisms". Applied and Environmental Microbiology 64, n. 3 (1 marzo 1998): 1143–46. http://dx.doi.org/10.1128/aem.64.3.1143-1146.1998.

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ABSTRACT Methanotrophs in enrichment cultures grew and sustained atmospheric methane oxidation when supplied with methanol. If they were not supplied with methanol or formate, their atmospheric methane oxidation came to a halt, but it was restored within hours in response to methanol or formate. Indigenous forest soil methanotrophs were also dependent on a supply of methanol upon reduced methane access but only when exposed to a methane-free atmosphere. Their immediate response to each methanol addition, however, was to shut down the oxidation of atmospheric methane and to reactivate atmospheric methane oxidation as the methanol was depleted.

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Benstead, J., G. M. King e H. G. Williams. "Methanol Promotes Atmospheric Methane Oxidation by Methanotrophic Cultures and Soils". Applied and Environmental Microbiology 64, n. 3 (1 marzo 1998): 1091–98. http://dx.doi.org/10.1128/aem.64.3.1091-1098.1998.

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ABSTRACT Two methanotrophic bacteria, Methylobacter albus BG8 and Methylosinus trichosporium OB3b, oxidized atmospheric methane during batch growth on methanol. Methane consumption was rapidly and substantially diminished (95% over 9 days) when washed cell suspensions were incubated without methanol in the presence of atmospheric methane (1.7 ppm). Methanotrophic activity was stimulated after methanol (10 mM) but not methane (1,000 ppm) addition. M. albus BG8 grown in continuous culture for 80 days with methanol retained the ability to oxidize atmospheric methane and oxidized methane in a chemostat air supply. Methane oxidation during growth on methanol was not affected by methane deprivation. Differences in the kinetics of methane uptake (apparent Km andV max) were observed between batch- and chemostat-grown cultures. The V max and apparent Km values (means ± standard errors) for methanol-limited chemostat cultures were 133 ± 46 nmol of methane 108 cells−1 h−1and 916 ± 235 ppm of methane (1.2 μM), respectively. These values were significantly lower than those determined with batch-grown cultures (V max of 648 ± 195 nmol of methane 108 cells−1 h−1 and apparent Km of 5,025 ± 1,234 ppm of methane [6.3 μM]). Methane consumption by soils was stimulated by the addition of methanol. These results suggest that methanol or other nonmethane substrates may promote atmospheric methane oxidation in situ.

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Stevens, C. M. "Atmospheric methane". Chemical Geology 71, n. 1-3 (dicembre 1988): 11–21. http://dx.doi.org/10.1016/0009-2541(88)90102-7.

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Zhou, Wencai, Xueying Qiu, Yuheng Jiang, Yingying Fan, Shilei Wei, Dongxue Han, Li Niu e Zhiyong Tang. "Highly selective aerobic oxidation of methane to methanol over gold decorated zinc oxide via photocatalysis". Journal of Materials Chemistry A 8, n. 26 (2020): 13277–84. http://dx.doi.org/10.1039/d0ta02793f.

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Arora, Vivek K., Joe R. Melton e David Plummer. "An assessment of natural methane fluxes simulated by the CLASS-CTEM model". Biogeosciences 15, n. 15 (1 agosto 2018): 4683–709. http://dx.doi.org/10.5194/bg-15-4683-2018.

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Abstract. Natural methane emissions from wetlands and fire, and soil uptake of methane, simulated using the Canadian Land Surface Scheme and Canadian Terrestrial Ecosystem (CLASS-CTEM) modelling framework, over the historical 1850–2008 period, are assessed by using a one-box model of atmospheric methane burden. This one-box model also requires anthropogenic emissions and the methane sink in the atmosphere to simulate the historical evolution of global methane burden. For this purpose, global anthropogenic methane emissions for the period 1850–2008 were reconstructed based on the harmonized representative concentration pathway (RCP) and Emission Database for Global Atmospheric Research (EDGAR) data sets. The methane sink in the atmosphere is represented using bias-corrected methane lifetimes from the Canadian Middle Atmosphere Model (CMAM). The resulting evolution of atmospheric methane concentration over the historical period compares reasonably well with observation-based estimates (correlation = 0.99, root mean square error = 35 ppb). The modelled natural emissions are also assessed using an inverse procedure where the methane lifetimes required to reproduce the observed year-to-year increase in atmospheric methane burden are calculated based upon the specified global anthropogenic and modelled natural emissions that we have used here. These calculated methane lifetimes over the historical period fall within the uncertainty range of observation-based estimates. The present-day (2000–2008) values of modelled methane emissions from wetlands (169 Tg CH4 yr−1) and fire (27 Tg CH4 yr−1), methane uptake by soil (29 Tg CH4 yr−1), and the budget terms associated with overall anthropogenic and natural emissions are consistent with estimates reported in a recent global methane budget that is based on top-down approaches constrained by observed atmospheric methane burden. The modelled wetland emissions increase over the historical period in response to both increases in precipitation and in atmospheric CO2 concentration. This increase in wetland emissions over the historical period yields evolution of the atmospheric methane concentration that compares better with observation-based values than the case when wetland emissions are held constant over the historical period.

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Catling, D. C., M. W. Claire e K. J. Zahnle. "Anaerobic methanotrophy and the rise of atmospheric oxygen". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, n. 1856 (18 maggio 2007): 1867–88. http://dx.doi.org/10.1098/rsta.2007.2047.

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In modern marine sediments, the anoxic decomposition of organic matter generates a significant flux of methane that is oxidized microbially with sulphate under the seafloor and never reaches the atmosphere. In contrast, prior to ca 2.4 Gyr ago, the ocean had little sulphate to support anaerobic oxidation of methane (AOM) and the ocean should have been an important methane source. As atmospheric O 2 and seawater sulphate levels rose on the early Earth, AOM would have increasingly throttled the release of methane. We use a biogeochemical model to simulate the response of early atmospheric O 2 and CH 4 to changes in marine AOM as sulphate levels increased. Semi-empirical relationships are used to parameterize global AOM rates and the evolution of sulphate levels. Despite broad uncertainties in these relationships, atmospheric O 2 concentrations generally rise more rapidly and to higher levels (of order approx. 10 −3 bar versus approx. 10 −4 bar) as a result of including AOM in the model. Methane levels collapse prior to any significant rise in O 2 , but counter-intuitively, methane re-rises after O 2 rises to higher levels when AOM is included. As O 2 concentrations increase, shielding of the troposphere by stratospheric ozone slows the effective reaction rate between oxygen and methane. This effect dominates over the decrease in the methane source associated with AOM. Thus, even with the inclusion of AOM, the simulated Late Palaeoproterozoic atmosphere has a climatologically significant level of methane of approximately 50 ppmv.

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Yarakhmedov, M. B., A. G. Kiiamov, M. E. Semenov, A. P. Semenov e A. S. Stoporev. "Peculiarities of Decomposition of Gas Hydrates in the Presence of Methanol at Atmospheric Pressure". Chemistry and Technology of Fuels and Oils 634, n. 6 (2022): 40–43. http://dx.doi.org/10.32935/0023-1169-2022-634-6-40-43.

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The study of the decomposition process of gas hydrates at atmospheric pressure and temperatures below 0°C revealed that methanol could affect this process in different ways, depending on its saturation with environmental components. Indeed, dueto the absorption of methane from the hydrate by methanol, the onset of its decomposition is observed at lower temperatures.Nevertheless, decomposition proceeds more slowly than with pure methane hydrate. When the methanol surrounding the methane hydrate is saturated with other medium components, the hydrate dissociation occurs at the equilibrium temperature (when intersecting the hydrate-ice-gas curve in a system without additives) regardless of the alcohol concentration. A similar situation is observed with hydrate obtained from a methane-propane gas mixture; however, under experimental conditions, ice beginsto melt at a lower temperature compared to the dissociation point of methane-propane hydrate (in the case of methane hydrate, the situation is reversed: the hydrate is less stable). High concentrations of methanol (above 40 mass%) lead to a significant decrease in the temperature of hydrate decomposition. The data obtained show that methanol in low dosages (about 10 mass%) can be usedfor gas storage and transportation since, under certain conditions, it does not shift the equilibrium curve of hydrate formation and slows down the process of methane hydrate decomposition.

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Keppler, Frank, Mihály Boros, Christian Frankenberg, Jos Lelieveld, Andrew McLeod, Anna Maria Pirttilä, Thomas Röckmann e Jörg-Peter Schnitzler. "Methane formation in aerobic environments". Environmental Chemistry 6, n. 6 (2009): 459. http://dx.doi.org/10.1071/en09137.

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Environmental context. Methane is an important greenhouse gas and its atmospheric concentration has drastically increased since pre-industrial times. Until recently biological methane formation has been associated exclusively with anoxic environments and microbial activity. In this article we discuss several alternative formation pathways of methane in aerobic environments and suggest that non-microbial methane formation may be ubiquitous in terrestrial and marine ecosystems. Abstract. Methane (CH4), the second principal anthropogenic greenhouse gas after CO2, is the most abundant reduced organic compound in the atmosphere and plays a central role in atmospheric chemistry. Therefore a comprehensive understanding of its sources and sinks and the parameters that control emissions is prerequisite to simulate past, present and future atmospheric conditions. Until recently biological CH4 formation has been associated exclusively with anoxic environments and methanogenic activity. However, there is growing and convincing evidence of alternative pathways in the aerobic biosphere including terrestrial plants, soils, marine algae and animals. Identifying and describing these sources is essential to complete our understanding of the biogeochemical cycles that control CH4 in the atmospheric environment and its influence as a greenhouse gas.

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9

Smith, H. J. "ATMOSPHERIC SCIENCE: Sourcing Methane". Science 316, n. 5826 (11 maggio 2007): 799b. http://dx.doi.org/10.1126/science.316.5826.799b.

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10

Wilson, Jason. "Natural atmospheric methane contributions". Marine Pollution Bulletin 28, n. 4 (aprile 1994): 194–95. http://dx.doi.org/10.1016/0025-326x(94)90085-x.

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11

Badr, O., S. D. Probert e P. W. O'Callaghan. "Origins of atmospheric methane". Applied Energy 40, n. 3 (gennaio 1991): 189–231. http://dx.doi.org/10.1016/0306-2619(91)90057-5.

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Badr, O., S. D. Probert e P. W. O'Callaghan. "Sinks for atmospheric methane". Applied Energy 41, n. 2 (gennaio 1992): 137–47. http://dx.doi.org/10.1016/0306-2619(92)90041-9.

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13

Buzan, E. M., C. A. Beale, C. D. Boone e P. F. Bernath. "Global stratospheric measurements of the isotopologues of methane from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer". Atmospheric Measurement Techniques Discussions 8, n. 10 (29 ottobre 2015): 11171–207. http://dx.doi.org/10.5194/amtd-8-11171-2015.

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Abstract. This paper presents an analysis of observations of methane and its two major isotopologues, CH3D and 13CH4 from the Atmospheric Chemistry Experiment (ACE) satellite between 2004 and 2013. Additionally, atmospheric methane chemistry is modeled using the Whole Atmospheric Community Climate Model (WACCM). ACE retrievals of methane extend from 6 km for all isotopologues to 75 km for 12CH4, 35 km for CH3D, and 50 km for 13CH4. While total methane concentrations retrieved from ACE agree well with the model, values of δD–CH4 and δ13C–CH4 show a bias toward higher δ compared to the model and balloon-based measurements. Calibrating δD and δ13C from ACE using WACCM in the troposphere gives improved agreement in δD in the stratosphere with the balloon measurements, but values of δ13C still disagree. A model analysis of methane's atmospheric sinks is also performed.

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Berchet, Antoine, Philippe Bousquet, Isabelle Pison, Robin Locatelli, Frédéric Chevallier, Jean-Daniel Paris, Ed J. Dlugokencky et al. "Atmospheric constraints on the methane emissions from the East Siberian Shelf". Atmospheric Chemistry and Physics 16, n. 6 (30 marzo 2016): 4147–57. http://dx.doi.org/10.5194/acp-16-4147-2016.

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Abstract. Subsea permafrost and hydrates in the East Siberian Arctic Shelf (ESAS) constitute a substantial carbon pool, and a potentially large source of methane to the atmosphere. Previous studies based on interpolated oceanographic campaigns estimated atmospheric emissions from this area at 8–17 TgCH4 yr−1. Here, we propose insights based on atmospheric observations to evaluate these estimates. The comparison of high-resolution simulations of atmospheric methane mole fractions to continuous methane observations during the whole year 2012 confirms the high variability and heterogeneity of the methane releases from ESAS. A reference scenario with ESAS emissions of 8 TgCH4 yr−1, in the lower part of previously estimated emissions, is found to largely overestimate atmospheric observations in winter, likely related to overestimated methane leakage through sea ice. In contrast, in summer, simulations are more consistent with observations. Based on a comprehensive statistical analysis of the observations and of the simulations, annual methane emissions from ESAS are estimated to range from 0.0 to 4.5 TgCH4 yr−1. Isotopic observations suggest a biogenic origin (either terrestrial or marine) of the methane in air masses originating from ESAS during late summer 2008 and 2009.

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Mazánková, V., L. Töröková, D. Trunec, F. Krčma, S. Matejčík e N. J. Mason. "Diagnostics of Nitrogen-methane Atmospheric Glow Discharge Used for a Mimic of Prebiotic Atmosphere". PLASMA PHYSICS AND TECHNOLOGY 4, n. 1 (2017): 83–86. http://dx.doi.org/10.14311/ppt.2017.1.83.

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The exploration of planetary atmosphere is being advanced by the exciting results of the Cassin-Huygens mission to Titan. The complex chemistry revealed in such atmospheres leading to the synthesis of bigger molecules is providing new insights into our understanding of how life on Earth developed. This work extends our previous investigation of nitrogen-methane (N2-CH4) atmospheric glow discharge for simulation chemical processes in prebiotic atmospheres. In presented experiments 2 % of water vapor were addet to nitrogen-methane gas mixture. Exhaust products of discharge in this gas mixture were in-situ analysed by Fourier Transform Infra Red spectroscopy (FTIR). The major products identified in spectra were: hydrogen cyanide, acetylene and acetonitrile.

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Meng, L., R. Paudel, P. G. M. Hess e N. M. Mahowald. "Seasonal and interannual variability in wetland methane emissions simulated by CLM4Me' and CAM-chem and comparisons to observations of concentrations". Biogeosciences 12, n. 13 (3 luglio 2015): 4029–49. http://dx.doi.org/10.5194/bg-12-4029-2015.

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Abstract. Understanding the temporal and spatial variation of wetland methane emissions is essential to the estimation of the global methane budget. Our goal for this study is three-fold: (i) to evaluate the wetland methane fluxes simulated in two versions of the Community Land Model, the Carbon-Nitrogen (CN; i.e., CLM4.0) and the Biogeochemistry (BGC; i.e., CLM4.5) versions using the methane emission model CLM4Me' so as to determine the sensitivity of the emissions to the underlying carbon model; (ii) to compare the simulated atmospheric methane concentrations to observations, including latitudinal gradients and interannual variability so as to determine the extent to which the atmospheric observations constrain the emissions; (iii) to understand the drivers of seasonal and interannual variability in atmospheric methane concentrations. Simulations of the transport and removal of methane use the Community Atmosphere Model with chemistry (CAM-chem) model in conjunction with CLM4Me' methane emissions from both CN and BGC simulations and other methane emission sources from literature. In each case we compare model-simulated atmospheric methane concentration with observations. In addition, we simulate the atmospheric concentrations based on the TransCom wetland and rice paddy emissions derived from a different terrestrial ecosystem model, Vegetation Integrative Simulator for Trace gases (VISIT). Our analysis indicates CN wetland methane emissions are higher in the tropics and lower at high latitudes than emissions from BGC. In CN, methane emissions decrease from 1993 to 2004 while this trend does not appear in the BGC version. In the CN version, methane emission variations follow satellite-derived inundation wetlands closely. However, they are dissimilar in BGC due to its different carbon cycle. CAM-chem simulations with CLM4Me' methane emissions suggest that both prescribed anthropogenic and predicted wetlands methane emissions contribute substantially to seasonal and interannual variability in atmospheric methane concentration. Simulated atmospheric CH4 concentrations in CAM-chem are highly correlated with observations at most of the 14 measurement stations evaluated with an average correlation between 0.71 and 0.80 depending on the simulation (for the period of 1993–2004 for most stations based on data availability). Our results suggest that different spatial patterns of wetland emissions can have significant impacts on Northern and Southern hemisphere (N–S) atmospheric CH4 concentration gradients and growth rates. This study suggests that both anthropogenic and wetland emissions have significant contributions to seasonal and interannual variations in atmospheric CH4 concentrations. However, our analysis also indicates the existence of large uncertainties in terms of spatial patterns and magnitude of global wetland methane budgets, and that substantial uncertainty comes from the carbon model underlying the methane flux modules.

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Meng, L., R. Paudel, P. G. M. Hess e N. M. Mahowald. "Seasonal and inter-annual variability in wetland methane emissions simulated by CLM4Me' and CAM-chem and comparisons to observations of concentrations". Biogeosciences Discussions 12, n. 3 (2 febbraio 2015): 2161–212. http://dx.doi.org/10.5194/bgd-12-2161-2015.

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Abstract. Understanding the temporal and spatial variation of wetland methane emissions is essential to the estimation of the global methane budget. We examine the seasonal and inter-annual variability in wetland methane emissions simulated in the Community Land Model (CLM4Me'). Methane emissions from both the Carbon-Nitrogen (CN, i.e. CLM4.0) and the Biogeochemistry (BGC, i.e. CLM4.5) versions of the CLM are evaluated. We further conduct simulations of the transport and removal of methane using the Community Atmosphere Model (CAM-chem) model using CLM4Me' methane emissions from both CN and BGC along with other methane sources and compare model simulated atmospheric methane concentration with observations. In addition, we simulate the atmospheric concentrations based on the TransCom wetland and rice paddy emissions from a different terrestrial ecosystem model VISIT. Our analysis suggests CN wetland methane emissions are higher in tropics and lower in high latitudes than BGC. In CN, methane emissions decrease from 1993 to 2004 while this trend does not appear in the BGC version. In the CN versions, methane emission variations follow satellite-derived inundation wetlands closely. However, they are dissimilar in BGC due to its different carbon cycle. CAM-chem model simulations with CLM4Me' methane emissions suggest that both prescribed anthropogenic and predicted wetlands methane emissions contribute substantially to seasonal and inter-annual variability in atmospheric methane concentration. It also suggests that different spatial patterns of wetland emissions can have significant impacts on N–S atmospheric CH4 concentration gradients and growth rates. This study suggests that large uncertainties still exist in terms of spatial patterns and magnitude of global wetland methane budgets, and that substantial uncertainty comes from the carbon model underlying the methane flux modules.

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Jackson, Robert B., Sam Abernethy, Josep G. Canadell, Matteo Cargnello, Steven J. Davis, Sarah Féron, Sabine Fuss et al. "Atmospheric methane removal: a research agenda". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n. 2210 (27 settembre 2021): 20200454. http://dx.doi.org/10.1098/rsta.2020.0454.

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Atmospheric methane removal (e.g. in situ methane oxidation to carbon dioxide) may be needed to offset continued methane release and limit the global warming contribution of this potent greenhouse gas. Because mitigating most anthropogenic emissions of methane is uncertain this century, and sudden methane releases from the Arctic or elsewhere cannot be excluded, technologies for methane removal or oxidation may be required. Carbon dioxide removal has an increasingly well-established research agenda and technological foundation. No similar framework exists for methane removal. We believe that a research agenda for negative methane emissions—‘removal' or atmospheric methane oxidation—is needed. We outline some considerations for such an agenda here, including a proposed Methane Removal Model Intercomparison Project (MR-MIP). This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

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Stevenson, David S., Richard G. Derwent, Oliver Wild e William J. Collins. "COVID-19 lockdown emission reductions have the potential to explain over half of the coincident increase in global atmospheric methane". Atmospheric Chemistry and Physics 22, n. 21 (8 novembre 2022): 14243–52. http://dx.doi.org/10.5194/acp-22-14243-2022.

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Abstract. Compared with 2019, measurements of the global growth rate of background (marine air) atmospheric methane rose by 5.3 ppb yr−1 in 2020, reaching 15.0 ppb yr−1. Global atmospheric chemistry models have previously shown that reductions in nitrogen oxide (NOx) emissions reduce levels of the hydroxyl radical (OH) and lengthen the methane lifetime. Acting in the opposite sense, reductions in carbon monoxide (CO) and non-methane volatile organic compound (NMVOC) emissions increase OH and shorten methane's lifetime. Using estimates of NOx, CO, and NMVOC emission reductions associated with COVID-19 lockdowns around the world in 2020 as well as model-derived regional and aviation sensitivities of methane to these emissions, we find that NOx emission reductions led to a 4.8 (3.8 to 5.8) ppb yr−1 increase in the global methane growth rate. Reductions in CO and NMVOC emissions partly counteracted this, changing (reducing) the methane growth rate by −1.4 (−1.1 to −1.7) ppb yr−1 (CO) and −0.5 (−0.1 to −0.9) ppb yr−1 (NMVOC), yielding a net increase of 2.9 (1.7 to 4.0) ppb yr−1. Uncertainties refer to ±1 standard deviation model ranges in sensitivities. Whilst changes in anthropogenic emissions related to COVID-19 lockdowns are probably not the only important factor that influenced methane during 2020, these results indicate that they have had a large impact and that the net effect of NOx, CO, and NMVOC emission changes can explain over half of the observed 2020 methane changes. Large uncertainties remain in both emission changes during the lockdowns and methane's response to them; nevertheless, this analysis suggests that further research into how the atmospheric composition changed over the lockdown periods will help us to interpret past methane changes and to constrain future methane projections.

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Berchet, A., P. Bousquet, I. Pison, R. Locatelli, F. Chevallier, J. D. Paris, E. J. Dlugokencky et al. "Atmospheric constraints on the methane emissions from the East Siberian Shelf". Atmospheric Chemistry and Physics Discussions 15, n. 18 (17 settembre 2015): 25477–501. http://dx.doi.org/10.5194/acpd-15-25477-2015.

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Abstract. Sub-sea permafrost and hydrates in the East Siberian Arctic Ocean Continental Shelf (ESAS) constitute a substantial carbon pool, and a potentially large source of methane to the atmosphere. Previous studies based on interpolated oceanographic campaigns estimated atmospheric emissions from this area at 8–17 Tg CH4 y−1. Here, we propose insights based on atmospheric observations to evaluate these estimates. Isotopic observations suggest a biogenic origin (either terrestrial or marine) of the methane in air masses originating from ESAS during summer 2010. The comparison of high-resolution simulations of atmospheric methane mole fractions to continuous methane observations during the entire year 2012 confirms the high variability and heterogeneity of the methane releases from ESAS. Simulated mole fractions including a 8 Tg CH4 y−1 source from ESAS are found largely overestimated compared to the observations in winter, whereas summer signals are more consistent with each other. Based on a comprehensive statistical analysis of the observations and of the simulations, annual methane emissions from ESAS are estimated in a range of 0.5–4.3 Tg CH4 y−1.

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Buzan, Eric M., Chris A. Beale, Chris D. Boone e Peter F. Bernath. "Global stratospheric measurements of the isotopologues of methane from the Atmospheric Chemistry Experiment Fourier transform spectrometer". Atmospheric Measurement Techniques 9, n. 3 (18 marzo 2016): 1095–111. http://dx.doi.org/10.5194/amt-9-1095-2016.

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Abstract. This paper presents an analysis of observations of methane and its two major isotopologues, CH3D and 13CH4, from the Atmospheric Chemistry Experiment (ACE) satellite between 2004 and 2013. Additionally, atmospheric methane chemistry is modeled using the Whole Atmospheric Community Climate Model (WACCM). ACE retrievals of methane extend from 6 km for all isotopologues to 75 km for 12CH4, 35 km for CH3D, and 50 km for 13CH4. While total methane concentrations retrieved from ACE agree well with the model, values of δD–CH4 and δ13C–CH4 show a bias toward higher δ compared to the model and balloon-based measurements. Errors in spectroscopic constants used during the retrieval process are the primary source of this disagreement. Calibrating δD and δ13C from ACE using WACCM in the troposphere gives improved agreement in δD in the stratosphere with the balloon measurements, but values of δ13C still disagree. A model analysis of methane's atmospheric sinks is also performed.

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Tveit, Alexander T., Anne Grethe Hestnes, Serina L. Robinson, Arno Schintlmeister, Svetlana N. Dedysh, Nico Jehmlich, Martin von Bergen et al. "Widespread soil bacterium that oxidizes atmospheric methane". Proceedings of the National Academy of Sciences 116, n. 17 (8 aprile 2019): 8515–24. http://dx.doi.org/10.1073/pnas.1817812116.

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The global atmospheric level of methane (CH4), the second most important greenhouse gas, is currently increasing by ∼10 million tons per year. Microbial oxidation in unsaturated soils is the only known biological process that removes CH4from the atmosphere, but so far, bacteria that can grow on atmospheric CH4have eluded all cultivation efforts. In this study, we have isolated a pure culture of a bacterium, strain MG08 that grows on air at atmospheric concentrations of CH4[1.86 parts per million volume (p.p.m.v.)]. This organism, namedMethylocapsa gorgona, is globally distributed in soils and closely related to uncultured members of the upland soil cluster α. CH4oxidation experiments and13C-single cell isotope analyses demonstrated that it oxidizes atmospheric CH4aerobically and assimilates carbon from both CH4and CO2. Its estimated specific affinity for CH4(a0s) is the highest for any cultivated methanotroph. However, growth on ambient air was also confirmed forMethylocapsa acidiphilaandMethylocapsa aurea, close relatives with a lower specific affinity for CH4, suggesting that the ability to utilize atmospheric CH4for growth is more widespread than previously believed. The closed genome ofM. gorgonaMG08 encodes a single particulate methane monooxygenase, the serine cycle for assimilation of carbon from CH4and CO2, and CO2fixation via the recently postulated reductive glycine pathway. It also fixes dinitrogen and expresses the genes for a high-affinity hydrogenase and carbon monoxide dehydrogenase, suggesting that atmospheric CH4oxidizers harvest additional energy from oxidation of the atmospheric trace gases carbon monoxide (0.2 p.p.m.v.) and hydrogen (0.5 p.p.m.v.).

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Zazzeri, Giulia, Dave Lowry, Rebecca E. Fisher, James L. France, Mathias Lanoisellé, Bryce F. J. Kelly, Jaroslaw M. Necki et al. "Carbon isotopic signature of coal-derived methane emissions to the atmosphere: from coalification to alteration". Atmospheric Chemistry and Physics 16, n. 21 (3 novembre 2016): 13669–80. http://dx.doi.org/10.5194/acp-16-13669-2016.

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Abstract. Currently, the atmospheric methane burden is rising rapidly, but the extent to which shifts in coal production contribute to this rise is not known. Coalbed methane emissions into the atmosphere are poorly characterised, and this study provides representative δ13CCH4 signatures of methane emissions from specific coalfields. Integrated methane emissions from both underground and opencast coal mines in the UK, Australia and Poland were sampled and isotopically characterised. Progression in coal rank and secondary biogenic production of methane due to incursion of water are suggested as the processes affecting the isotopic composition of coal-derived methane. An averaged value of −65 ‰ has been assigned to bituminous coal exploited in open cast mines and of −55 ‰ in deep mines, whereas values of −40 and −30 ‰ can be allocated to anthracite opencast and deep mines respectively. However, the isotopic signatures that are included in global atmospheric modelling of coal emissions should be region- or nation-specific, as greater detail is needed, given the wide global variation in coal type.

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Turner, Alexander J., Christian Frankenberg e Eric A. Kort. "Interpreting contemporary trends in atmospheric methane". Proceedings of the National Academy of Sciences 116, n. 8 (7 febbraio 2019): 2805–13. http://dx.doi.org/10.1073/pnas.1814297116.

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Atmospheric methane plays a major role in controlling climate, yet contemporary methane trends (1982–2017) have defied explanation with numerous, often conflicting, hypotheses proposed in the literature. Specifically, atmospheric observations of methane from 1982 to 2017 have exhibited periods of both increasing concentrations (from 1982 to 2000 and from 2007 to 2017) and stabilization (from 2000 to 2007). Explanations for the increases and stabilization have invoked changes in tropical wetlands, livestock, fossil fuels, biomass burning, and the methane sink. Contradictions in these hypotheses arise because our current observational network cannot unambiguously link recent methane variations to specific sources. This raises some fundamental questions: (i) What do we know about sources, sinks, and underlying processes driving observed trends in atmospheric methane? (ii) How will global methane respond to changes in anthropogenic emissions? And (iii), What future observations could help resolve changes in the methane budget? To address these questions, we discuss potential drivers of atmospheric methane abundances over the last four decades in light of various observational constraints as well as process-based knowledge. While uncertainties in the methane budget exist, they should not detract from the potential of methane emissions mitigation strategies. We show that net-zero cost emission reductions can lead to a declining atmospheric burden, but can take three decades to stabilize. Moving forward, we make recommendations for observations to better constrain contemporary trends in atmospheric methane and to provide mitigation support.

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SHUKLA, J. B., SHYAM SUNDAR, ASHISH KUMAR MISHRA e RAM NARESH. "NUMERICAL MODEL ON METHANE EMISSIONS FROM AGRICULTURE SECTOR". International Journal of Big Data Mining for Global Warming 02, n. 01 (giugno 2020): 2050003. http://dx.doi.org/10.1142/s2630534820500035.

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Atmospheric methane, emitted from agriculture sector such as production of rice paddies and farming of livestock populations, is one of the important factors responsible for increasing the average atmospheric temperature leading to global warming. It is, therefore, crucial to comprehend the dynamics of methane emission and its effect on global warming. In this paper, a nonlinear mathematical model is proposed and analyzed to study the increase of average atmospheric temperature (or average global warming temperature) caused by emission of methane due to various processes involved in the production of rice paddies and farming of livestock populations simultaneously. In the modeling process, six variables are considered, namely, the cumulative biomass density of rice paddies, the cumulative density of livestock populations, the cumulative density of methane formed by various processes involved in the production of rice paddies, the cumulative density of methane formed by various processes involved in the farming of livestock populations, the atmospheric concentration of methane and the average atmospheric temperature. It is assumed that both the cumulative biomass densities of rice paddies and livestock populations follow logistic models with their respective growth rates and carrying capacities. The growth rate of concentration of methane in the atmosphere is assumed to be directly proportional to the cumulative densities of various processes involved in the production of rice paddies as well as in the farming of livestock populations. This growth rate also increases with a constant rate from various natural sources such as wetlands, etc. The growth rate of average global warming temperature is assumed to be proportional to the increased level of methane concentration in the atmosphere from its equilibrium value. It is also assumed that this temperature decreases with a rate proportional to its enhanced level from its equilibrium level caused by various natural factors such as rain fall, snowfall, etc. The proposed model is analyzed using the stability theory of differential equations and numerical simulation. The analysis shows that as the emission of methane from various processes involved in the production of rice paddies and farming of livestock populations increase, the average global warming temperature increases considerably from its equilibrium level. The numerical simulation of the model confirms the analytical results.

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26

Foschi, Martino, Joseph A. Cartwright, Christopher W. MacMinn e Giuseppe Etiope. "Evidence for massive emission of methane from a deep‐water gas field during the Pliocene". Proceedings of the National Academy of Sciences 117, n. 45 (26 ottobre 2020): 27869–76. http://dx.doi.org/10.1073/pnas.2001904117.

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Geologic hydrocarbon seepage is considered to be the dominant natural source of atmospheric methane in terrestrial and shallow‐water areas; in deep‐water areas, in contrast, hydrocarbon seepage is expected to have no atmospheric impact because the gas is typically consumed throughout the water column. Here, we present evidence for a sudden expulsion of a reservoir‐size quantity of methane from a deep‐water seep during the Pliocene, resulting from natural reservoir overpressure. Combining three-dimensional seismic data, borehole data and fluid‐flow modeling, we estimate that 18–27 of the 23–31 Tg of methane released at the seafloor could have reached the atmosphere over 39–241 days. This emission is ∼10% and ∼28% of present‐day, annual natural and petroleum‐industry methane emissions, respectively. While no such ultraseepage events have been documented in modern times and their frequency is unknown, seismic data suggest they were not rare in the past and may potentially occur at present in critically pressurized reservoirs. This neglected phenomenon can influence decadal changes in atmospheric methane.

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27

Topp, Edward, e Elizabeth Pattey. "Soils as sources and sinks for atmospheric methane". Canadian Journal of Soil Science 77, n. 2 (1 maggio 1997): 167–77. http://dx.doi.org/10.4141/s96-107.

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Methane is considered to be a significant greenhouse gas. Methane is produced in soils as the end product of the anaerobic decomposition of organic matter. In the absence of oxygen, methane is very stable, but under aerobic conditions it is mineralized to carbon dioxide by methanotrophic bacteria. Soil methane emissions, primarily from natural wetlands, landfills and rice paddies, are estimated to represent about half of the annual global methane production. Oxidation of atmospheric methane by well-drained soils accounts for about 10% of the global methane sink. Whether a soil is a net source or sink for methane depends on the relative rates of methanogenic and methanotrophic activity. A number of factors including pH, Eh, temperature and moisture content influence methane transforming bacterial populations and soil fluxes. Several techniques are available for measuring methane fluxes. Flux estimation is complicated by spatial and temporal variability. Soil management can impact methane transformations. For example, landfilling of organic matter can result in significant methane emissions, whereas some cultural practices such as nitrogen fertilization inhibit methane oxidation by agricultural soils. Key words: Methane, methanogenesis, methane oxidation, soil, flux measurement

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28

Bartdorff, Oliver, Klaus Wallmann, Mojib Latif e Vladimir Semenov. "Phanerozoic evolution of atmospheric methane". Global Biogeochemical Cycles 22, n. 1 (7 febbraio 2008): n/a. http://dx.doi.org/10.1029/2007gb002985.

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29

Cicerone, R. J., e R. S. Oremland. "Biogeochemical aspects of atmospheric methane". Global Biogeochemical Cycles 2, n. 4 (dicembre 1988): 299–327. http://dx.doi.org/10.1029/gb002i004p00299.

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30

Khalil, M. A. K., e R. A. Rasmussen. "Atmospheric methane: recent global trends". Environmental Science & Technology 24, n. 4 (aprile 1990): 549–53. http://dx.doi.org/10.1021/es00074a014.

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31

Wuebbles, D. "Atmospheric methane and global change". Earth-Science Reviews 57, n. 3-4 (maggio 2002): 177–210. http://dx.doi.org/10.1016/s0012-8252(01)00062-9.

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32

ZURER, PAMELA. "Rise in atmospheric methane probed". Chemical & Engineering News 65, n. 18 (4 maggio 1987): 22. http://dx.doi.org/10.1021/cen-v065n018.p022.

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33

Lelieveld, J., P. J. Crutzen e C. Brühl. "Climate effects of atmospheric methane". Chemosphere 26, n. 1-4 (gennaio 1993): 739–68. http://dx.doi.org/10.1016/0045-6535(93)90458-h.

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34

Jackson, R. B., E. I. Solomon, J. G. Canadell, M. Cargnello e C. B. Field. "Methane removal and atmospheric restoration". Nature Sustainability 2, n. 6 (20 maggio 2019): 436–38. http://dx.doi.org/10.1038/s41893-019-0299-x.

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35

Delmas, R. A., J. P. Tathy e B. Cros. "Atmospheric methane budget in Africa". Journal of Atmospheric Chemistry 14, n. 1-4 (aprile 1992): 395–409. http://dx.doi.org/10.1007/bf00115247.

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36

Xinke, Yu. "Another source of atmospheric methane". Chinese Journal of Geochemistry 16, n. 2 (aprile 1997): 189–92. http://dx.doi.org/10.1007/bf02843399.

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37

Ferretti, D. F., J. B. Miller, J. W. C. White, K. R. Lassey, D. C. Lowe e D. M. Etheridge. "Stable isotopes provide revised global limits of aerobic methane emissions from plants". Atmospheric Chemistry and Physics 7, n. 1 (17 gennaio 2007): 237–41. http://dx.doi.org/10.5194/acp-7-237-2007.

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Abstract (sommario):

Abstract. Recently Keppler et al. (2006) discovered a surprising new source of methane – terrestrial plants under aerobic conditions, with an estimated global production of 62–236 Tg yr−1 by an unknown mechanism. This is ~10–40% of the annual total of methane entering the modern atmosphere and ~30–100% of annual methane entering the pre-industrial (0 to 1700 AD) atmosphere. Here we test this reported global production of methane from plants against ice core records of atmospheric methane concentration (CH4) and stable carbon isotope ratios (δ13CH4) over the last 2000 years. Our top-down approach determines that global plant emissions must be much lower than proposed by Keppler et al. (2006) during the last 2000 years and are likely to lie in the range 0–46 Tg yr−1 and 0–176 Tg yr−1 during the pre-industrial and modern eras, respectively.

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38

Bange, Hermann W., Tom G. Bell, Marcela Cornejo, Alina Freing, Günther Uher, Rob C. Upstill-Goddard e Guiling Zhang. "MEMENTO: a proposal to develop a database of marine nitrous oxide and methane measurements". Environmental Chemistry 6, n. 3 (2009): 195. http://dx.doi.org/10.1071/en09033.

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Abstract (sommario):

Environmental context. Nitrous oxide and methane are atmospheric trace gases and, because they are strong greenhouse gases, they contribute significantly to the ongoing global warming of the Earth’s atmosphere. Despite the well established fact that the world’s oceans release nitrous oxide and methane to the atmosphere, the oceanic emission estimates of both gases are only poorly quantified. The MEMENTO (MarinE MethanE and NiTrous Oxide) database initiative is proposed as an effective way by which existing nitrous oxide and methane measurements can be used to reduce the uncertainty of the oceanic emissions estimates by establishing a global database.

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39

Joelsson, L. M. T., J. A. Schmidt, E. J. K. Nilsson, T. Blunier, D. W. T. Griffith, S. Ono e M. S. Johnson. "Kinetic isotope effects of 12CH3D + OH and 13CH3D + OH from 278 to 313 K". Atmospheric Chemistry and Physics 16, n. 7 (11 aprile 2016): 4439–49. http://dx.doi.org/10.5194/acp-16-4439-2016.

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Abstract. Methane is the second most important long-lived greenhouse gas and plays a central role in the chemistry of the Earth's atmosphere. Nonetheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including the doubly substituted species 13CH3D, offers new insight into the methane budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH in the troposphere, which accounts for around 84 % of all methane removal. Here we present experimentally derived methane + OH kinetic isotope effects and their temperature dependence over the range of 278 to 313 K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D = 1.31 ± 0.01 and kCH4/k13CH3D = 1.34 ± 0.03 at room temperature, implying that the methane + OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) = kCH4/k13CH3D, within the experimental uncertainty, given the literature value of kCH4/k13CH4 = 1.0039 ± 0.0002. In addition, the kinetic isotope effects were characterized using transition state theory with tunneling corrections. Good agreement between the experimental, quantum chemical, and available literature values was obtained. Based on the results we conclude that the OH reaction (the main sink of methane) at steady state can produce an atmospheric clumped isotope signal (Δ(13CH3D) = ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02. This implies that the bulk tropospheric Δ(13CH3D) reflects the source signal with relatively small adjustment due to the sink signal (i.e., mainly OH oxidation).

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40

Joelsson, L. M. T., J. A. Schmidt, E. J. K. Nilsson, T. Blunier, D. W. T. Griffith, S. Ono e M. S. Johnson. "Development of a new methane tracer: kinetic isotope effect of 13CH3D + OH from 278 to 313 K". Atmospheric Chemistry and Physics Discussions 15, n. 19 (15 ottobre 2015): 27853–75. http://dx.doi.org/10.5194/acpd-15-27853-2015.

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Abstract (sommario):

Abstract. Methane is the second most important long lived greenhouse gas and impacts the oxidative capacity of the Earth's atmosphere. Nontheless there are significant uncertainties in its source budget. Analysis of the isotopic composition of atmospheric methane, including doubly substituted species (e.g. 13CH3D), offers new constraints on the methane source budget as the sources and sinks have distinct isotopic signatures. The most important sink of atmospheric methane is oxidation by OH which accounts for around 90 % of methane removal in the troposphere. Here we present experimentally derived methane + OH kinetic isotope effects and their temperature dependence over the range of 278 to 313 K for CH3D and 13CH3D; the latter is reported here for the first time. We find kCH4/kCH3D=1.31 ± 0.01 and kCH4/k13CH3D = 1.34 ± 0.03 at room temperature, implying that the methane + OH kinetic isotope effect is multiplicative such that (kCH4/k13CH4)(kCH4/kCH3D) = kCH4/k13CH3D to within the experimental uncertainty. In addition the kinetic isotope effect were characterized using transition state theory with tunneling correction. Good agreement between the experimental, quantum chemical and available literature values was obtained. The theoretical calculations show that 13CH3D isotope effects is the product of D- and 13C-isotope effect. Based on the results we conclude that the OH reaction at steady-state can produce an atmospheric clumped isotope signal (Δ(13CH3D) = ln([CH4][13CH3D]/[13CH4][CH3D])) of 0.02 ± 0.02.

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41

Holmes, Andrew J., Peter Roslev, Ian R. McDonald, Niels Iversen, Kaj Henriksen e J. Colin Murrell. "Characterization of Methanotrophic Bacterial Populations in Soils Showing Atmospheric Methane Uptake". Applied and Environmental Microbiology 65, n. 8 (1 agosto 1999): 3312–18. http://dx.doi.org/10.1128/aem.65.8.3312-3318.1999.

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Abstract (sommario):

ABSTRACT The global methane cycle includes both terrestrial and atmospheric processes and may contribute to feedback regulation of the climate. Most oxic soils are a net sink for methane, and these soils consume approximately 20 to 60 Tg of methane per year. The soil sink for atmospheric methane is microbially mediated and sensitive to disturbance. A decrease in the capacity of this sink may have contributed to the ∼1% · year−1 increase in the atmospheric methane level in this century. The organisms responsible for methane uptake by soils (the atmospheric methane sink) are not known, and factors that influence the activity of these organisms are poorly understood. In this study the soil methane-oxidizing population was characterized by both labelling soil microbiota with14CH4 and analyzing a total soil monooxygenase gene library. Comparative analyses of [14C]phospholipid ester-linked fatty acid profiles performed with representative methane-oxidizing bacteria revealed that the soil sink for atmospheric methane consists of an unknown group of methanotrophic bacteria that exhibit some similarity to type II methanotrophs. An analysis of monooxygenase gene libraries from the same soil samples indicated that an unknown group of bacteria belonging to the α subclass of the class Proteobacteria was present; these organisms were only distantly related to extant methane-oxidizing strains. Studies on factors that affect the activity, population dynamics, and contribution to global methane flux of “atmospheric methane oxidizers” should be greatly facilitated by use of biomarkers identified in this study.

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42

Smith, Amy Tetlow. "Environmental factors affecting global atmospheric methane concentrations". Progress in Physical Geography: Earth and Environment 19, n. 3 (settembre 1995): 322–35. http://dx.doi.org/10.1177/030913339501900302.

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Abstract (sommario):

Methane is a greenhouse gas of largely biological origin. Micro-organisms responsible for production of much of the atmospheric methane are directly affected by climate resulting in potential feedbacks between the atmosphere and the biosphere. Our current understanding of the role of methane in the climate system is reviewed in this article, with a brief discussion of biological, chemical, and physical processes responsible for the spatial and temporal distribution of atmos pheric methane. The magnitude of most methane sources is highly speculative, and their distributions are qualitatively understood. Most terrestrial source regions have been surveyed, but few have been studied in much detail. The strength of enteric sources is based on laboratory measurements of emissions from a few animals and estimates of global populations. Accuracy of the resulting flux size and distribution is highly suspect. Data available on either magnitude or distribution of non-biogenic methane sources are scarce. Models of the influence of climate on biological methane sources are primarily regressions dependent on measures of heat and water in the environment. Process-based models derived from biological and physical principles are called for in order to address environmental conditions unlike the present.

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43

Lassey, K. R., D. C. Lowe e A. M. Smith. "The atmospheric cycling of radiomethane and the ''fossil fraction'' of the methane source". Atmospheric Chemistry and Physics Discussions 6, n. 3 (21 giugno 2006): 5039–56. http://dx.doi.org/10.5194/acpd-6-5039-2006.

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Abstract. The cycling of 14CH4 (''radiomethane'') through the atmosphere has been strongly perturbed in the industrial era by the release of 14C-free methane from geologic reservoirs (''fossil methane'' emissions), and in the nuclear era, especially since ca 1970, by the direct release of nucleogenic radiomethane from nuclear power facilities. Contemporary measurements of atmospheric radiomethane have been used to estimate the proportion of fossil methane in the global methane source (the ''fossil fraction''), but such estimates carry high uncertainty due to the ill-determined nuclear-power source. We exploit an analysis in a companion paper of the global radiomethane budget through the nuclear era, using contemporary measurements of atmospheric radiomethane since 1986 to quantify both the fossil fraction and the strength of the nuclear power source. We deduce that 28.6±1.9% (1 s.d.) of the global methane source has fossil origin, a fraction which may include some 14C-depleted refractory carbon fraction such as in aged peat deposits. The co-estimated strength of the global nuclear-power source of radiomethane is consistent with values inferred independently from local nuclear facilities.

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44

Maasakkers, Joannes D., Daniel J. Jacob, Melissa P. Sulprizio, Tia R. Scarpelli, Hannah Nesser, Jian-Xiong Sheng, Yuzhong Zhang et al. "Global distribution of methane emissions, emission trends, and OH concentrations and trends inferred from an inversion of GOSAT satellite data for 2010–2015". Atmospheric Chemistry and Physics 19, n. 11 (12 giugno 2019): 7859–81. http://dx.doi.org/10.5194/acp-19-7859-2019.

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Abstract. We use 2010–2015 observations of atmospheric methane columns from the GOSAT satellite instrument in a global inverse analysis to improve estimates of methane emissions and their trends over the period, as well as the global concentration of tropospheric OH (the hydroxyl radical, methane's main sink) and its trend. Our inversion solves the Bayesian optimization problem analytically including closed-form characterization of errors. This allows us to (1) quantify the information content from the inversion towards optimizing methane emissions and its trends, (2) diagnose error correlations between constraints on emissions and OH concentrations, and (3) generate a large ensemble of solutions testing different assumptions in the inversion. We show how the analytical approach can be used, even when prior error standard deviation distributions are lognormal. Inversion results show large overestimates of Chinese coal emissions and Middle East oil and gas emissions in the EDGAR v4.3.2 inventory but little error in the United States where we use a new gridded version of the EPA national greenhouse gas inventory as prior estimate. Oil and gas emissions in the EDGAR v4.3.2 inventory show large differences with national totals reported to the United Nations Framework Convention on Climate Change (UNFCCC), and our inversion is generally more consistent with the UNFCCC data. The observed 2010–2015 growth in atmospheric methane is attributed mostly to an increase in emissions from India, China, and areas with large tropical wetlands. The contribution from OH trends is small in comparison. We find that the inversion provides strong independent constraints on global methane emissions (546 Tg a−1) and global mean OH concentrations (atmospheric methane lifetime against oxidation by tropospheric OH of 10.8±0.4 years), indicating that satellite observations of atmospheric methane could provide a proxy for OH concentrations in the future.

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45

He, Jian, Vaishali Naik, Larry W. Horowitz, Ed Dlugokencky e Kirk Thoning. "Investigation of the global methane budget over 1980–2017 using GFDL-AM4.1". Atmospheric Chemistry and Physics 20, n. 2 (23 gennaio 2020): 805–27. http://dx.doi.org/10.5194/acp-20-805-2020.

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Abstract (sommario):

Abstract. Changes in atmospheric methane abundance have implications for both chemistry and climate as methane is both a strong greenhouse gas and an important precursor for tropospheric ozone. A better understanding of the drivers of trends and variability in methane abundance over the recent past is therefore critical for building confidence in projections of future methane levels. In this work, the representation of methane in the atmospheric chemistry model AM4.1 is improved by optimizing total methane emissions (to an annual mean of 580±34 Tg yr−1) to match surface observations over 1980–2017. The simulations with optimized global emissions are in general able to capture the observed trend, variability, seasonal cycle, and latitudinal gradient of methane. Simulations with different emission adjustments suggest that increases in methane emissions (mainly from agriculture, energy, and waste sectors) balanced by increases in methane sinks (mainly due to increases in OH levels) lead to methane stabilization (with an imbalance of 5 Tg yr−1) during 1999–2006 and that increases in methane emissions (mainly from agriculture, energy, and waste sectors) combined with little change in sinks (despite small decreases in OH levels) during 2007–2012 lead to renewed growth in methane (with an imbalance of 14 Tg yr−1 for 2007–2017). Compared to 1999–2006, both methane emissions and sinks are greater (by 31 and 22 Tg yr−1, respectively) during 2007–2017. Our tagged tracer analysis indicates that anthropogenic sources (such as agriculture, energy, and waste sectors) are more likely major contributors to the renewed growth in methane after 2006. A sharp increase in wetland emissions (a likely scenario) with a concomitant sharp decrease in anthropogenic emissions (a less likely scenario), would be required starting in 2006 to drive the methane growth by wetland tracer. Simulations with varying OH levels indicate that a 1 % change in OH levels could lead to an annual mean difference of ∼4 Tg yr−1 in the optimized emissions and a 0.08-year difference in the estimated tropospheric methane lifetime. Continued increases in methane emissions along with decreases in tropospheric OH concentrations during 2008–2015 prolong methane's lifetime and therefore amplify the response of methane concentrations to emission changes. Uncertainties still exist in the partitioning of emissions among individual sources and regions.

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46

MacAyeal, Douglas R., e Dean R. Lindstrom. "Effects of Glaciation on Methane-Hydrate Stability". Annals of Glaciology 14 (1990): 183–85. http://dx.doi.org/10.3189/s0260305500008533.

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Temperature and pressure changes within subglacial sediments caused by déglaciation favor a phase change from methane hydrate to methane gas. If released to the atmosphere, this gas could have contributed significantly to the increased atmospheric methane concentration during interglacial periods. Using a numerical reconstruction of sediment temperatures and ice-sheet loads, the total sediment volume in the Eurasian Arctic that is subject to this phase change is estimated to be 2.8 × 1014 m3.

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47

MacAyeal, Douglas R., e Dean R. Lindstrom. "Effects of Glaciation on Methane-Hydrate Stability". Annals of Glaciology 14 (1990): 183–85. http://dx.doi.org/10.1017/s0260305500008533.

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Abstract (sommario):

Temperature and pressure changes within subglacial sediments caused by déglaciation favor a phase change from methane hydrate to methane gas. If released to the atmosphere, this gas could have contributed significantly to the increased atmospheric methane concentration during interglacial periods. Using a numerical reconstruction of sediment temperatures and ice-sheet loads, the total sediment volume in the Eurasian Arctic that is subject to this phase change is estimated to be 2.8 × 1014 m3.

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48

Archer, D. "A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin". Biogeosciences 12, n. 10 (21 maggio 2015): 2953–74. http://dx.doi.org/10.5194/bg-12-2953-2015.

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Abstract. A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.

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49

Nisbet, Euan G., Edward J. Dlugokencky, Rebecca E. Fisher, James L. France, David Lowry, Martin R. Manning, Sylvia E. Michel e Nicola J. Warwick. "Atmospheric methane and nitrous oxide: challenges alongthe path to Net Zero". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 379, n. 2210 (27 settembre 2021): 20200457. http://dx.doi.org/10.1098/rsta.2020.0457.

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Abstract (sommario):

The causes of methane's renewed rise since 2007, accelerated growth from 2014 and record rise in 2020, concurrent with an isotopic shift to values more depleted in 13 C, remain poorly understood. This rise is the dominant departure from greenhouse gas scenarios that limit global heating to less than 2°C. Thus a comprehensive understanding of methane sources and sinks, their trends and inter-annual variations are becoming more urgent. Efforts to quantify both sources and sinks and understand latitudinal and seasonal variations will improve our understanding of the methane cycle and its anthropogenic component. Nationally declared emissions inventories under the UN Framework Convention on Climate Change (UNFCCC) and promised contributions to emissions reductions under the UNFCCC Paris Agreement need to be verified independently by top-down observation. Furthermore, indirect effects on natural emissions, such as changes in aquatic ecosystems, also need to be quantified. Nitrous oxide is even more poorly understood. Despite this, options for mitigating methane and nitrous oxide emissions are improving rapidly, both in cutting emissions from gas, oil and coal extraction and use, and also from agricultural and waste sources. Reductions in methane and nitrous oxide emission are arguably among the most attractive immediate options for climate action. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.

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50

Borowski, Marek, Piotr Życzkowski, Rafał Łuczak, Michał Karch e Jianwei Cheng. "Tests to Ensure the Minimum Methane Concentration for Gas Engines to Limit Atmospheric Emissions". Energies 13, n. 1 (20 dicembre 2019): 44. http://dx.doi.org/10.3390/en13010044.

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During the extraction of hard coal in Polish conditions, methane is emitted, which is referred to as ‘mine gas’. As a result of the desorption of methane, a greenhouse gas is released from coal seams. In order to reduce atmospheric emissions, methane from coal seams is captured by a methane drainage system. On the other hand, methane, which has been separated into underground mining excavations, is discharged into the atmosphere with a stream of ventilation air. For many years, Polish hard coal mines have been capturing methane to ensure the safety of the crew and the continuity of mining operations. As a greenhouse gas, methane has a significant potential, as it is more effective at absorbing and re-emitting radiation than carbon dioxide. The increase in the amount of methane in the atmosphere is a significant factor influencing global warming, however, it is not as strong as the increase in carbon dioxide. Therefore, in Polish mines, the methane–air mixture captured in the methane drainage system is not emitted to the atmosphere, but burned as fuel in systems, including cogeneration systems, to generate electricity, heat and cold. However, in order for such use to be possible, the methane–air mixture must meet appropriate quality and quantity requirements. The article presents an analysis of changes in selected parameters of the captured methane–air mixture from one of the hard coal mines in the Upper Silesian Coal Basin in Poland. The paper analyses the changes in concentration and size of the captured methane stream through the methane capturing system. The gas captured by the methane drainage system, as an energy source, can be used in cogeneration, when the methane concentration is greater than 40%. Considering the variability of CH4 concentration in the captured mixture, it was also indicated which pure methane stream must be added to the gas mixture in order for this gas to be used as a fuel for gas engines. The balance of power of produced electric energy in gas engines is presented. Possible solutions ensuring constant concentration of the captured methane–air mixture are also presented.

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