Dissertations / Theses: 'Atmospheric methane'

1

Tice, Dane Steven. "Ground-based near-infrared remote sounding of ice giant clouds and methane." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:4f09f270-a25c-4d36-96d3-13070a594eaa.

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The ice giants, Uranus and Neptune, are the two outermost planets in our solar system. With only one satellite flyby each in the late 1980’s, the ice giants are arguably the least understood of the planets orbiting the Sun. A better understanding of these planets’ atmospheres will not only help satisfy the natural scientific curiosity we have about these distant spheres of gas, but also might provide insight into the dynamics and meteorology of our own planet’s atmosphere. Two new ground-based, near-infrared datasets of the ice giants are studied. Both datasets provide data in a portion of the electromagnetic spectrum that provides good constraint on the size of small scattering particles in the atmospheres’ clouds and haze layers. The broad extent of both telescopes’ spectral coverage allows characterisation of these small particles for a wide range of wavelengths. Both datasets also provide coverage of the 825 nm collision-induced hydrogen-absorption feature, allowing us to disentangle the latitudinal variation of CH4 abundance from the height and vertical extent of clouds in the upper troposphere. A two-cloud model is successfully fitted to IRTF SpeX Uranus data, parameterising both clouds with base altitude, fractional scale height, and total opacity. An optically thick, vertically thin cloud with a base pressure of 1.6 bar, tallest in the midlatitudes, shows strong preference for scattering particles of 1.35 μm radii. Above this cloud lies an optically thin, vertically extended haze extending upward from 1.0 bar and consistent with particles of 0.10 μm radii. An equatorial enrichment of methane abundance and a lower cloud of constant vertical thickness was shown to exist using two independent methods of analysis. Data from Palomar SWIFT of three different latitude regions.

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2

Knappett, Diane Shirley. "Observing the distribution of atmospheric methane from space." Thesis, University of Leicester, 2012. http://hdl.handle.net/2381/10928.

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Methane (CH4) is a potent greenhouse gas with a radiative forcing efficiency 21 times greater than that of carbon dioxide (CO2) and an atmospheric lifetime of approximately 12 years. Although the annual global source strength of CH4 is fairly well constrained, the temporal and spatial variability of individual sources and sinks is currently less well quantified. In order to constrain CH4 emission estimates, inversion models require satellite retrievals of XCH4 with an accuracy of < 1-2%. However, satellite retrievals of XCH4 in the shortwave infrared (SWIR) are often hindered by the presence of atmospheric aerosols and/or thin ice (cirrus) clouds which can lead to biases in the resulting trace gas total column of comparable magnitude. This thesis aims to quantify the magnitude of retrieval errors caused by aerosol and cirrus cloud induced scattering for the Full Spectral Initiation Weighting Function Modified Differential Optical Absorption Spectroscopy (FSI WFM-DOAS) retrieval algorithm. A series of sensitivity tests have been performed which reveal that a) for scenes of high optical depth, accurate aerosol a priori data is required to reduce retrieval errors, b) retrieval errors due to aerosol and ice cloud scattering are highly dependent on surface albedo, SZA and the altitude at which scattering occurs and c) errors induced in global retrievals by the presence of ice clouds (up to ~ 35%) are significantly greater than those owing to aerosols (~ 1-2%). Cloud filtering is therefore important even when employing proxy methods. Furthermore, the original FSI WFM-DOAS V2 algorithm (OFSI) has been successfully modified with improved a priori albedo and aerosol, resulting in two new versions of the retrieval: MFSI and GFSI. Initial comparison of OFSI, MFSI and GFSI retrievals of XCH4 over North America show minor improvements in retrieval error, however further comparison over regions of high optical depth are required.

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3

Warwick, Nicola Julie. "Global modelling of atmospheric methane and methyl bromide." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619980.

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4

Teama, Doaa Galal. "A 30-Year Record of the Isotopic Composition of Atmospheric Methane." Thesis, Portland State University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3557627.

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Methane (CH4) is one of the most important greenhouse gases after water vapor and carbon dioxide due to its high concentration and global warming potential 25 times than that of CO2(based on a 100 year time horizon). Its atmospheric concentration has more than doubled from the preindustrial era due to anthropogenic activities such as rice cultivation, biomass burning, and fossil fuel production. However, the rate of increase of atmospheric CH4 (or the growth rate) slowed from 1980 until present. The main reason for this trend is a slowdown in the trend of CH 4sources. Measuring stable isotopes of atmospheric CH4 can constrain changes of CH4sources. The main goal of this work is to interpret the CH4 trend from 1978-2010 in terms of its sources using measurements of CH4 mixing ratio and its isotopes. The current work presents the measurements and analysis of CH4 and its isotopes (δ13C and δD) of four air archive sample sets collected by the Oregon Graduate Institute (OGI). CH4 isotope ratios (δ13C and δD) were measured by a continuous flow isotope ratio mass spectrometer technique developed at PSU. The first set is for Cape Meares, Oregon which is the oldest and longest set and spans 1977-1999. The integrity of this sample set was evaluated by comparing between our measured CH4 mixing ratio values with those measured values by OGI and was found to be stable. Resulting CH4 seasonal cycle was evaluated from the Cape Meares data. The CH4 seasonal cycle shows a broad maximum during October-April and a minimum between July and August. The seasonal cycles of δ13C and δD have maximum values in May for δ13C and in July for δD and minimum values between September-October for δ13C and in October for δD. These results indicate a CH4 source that is more enriched January-May (e.g. biomass burning) and a source that is more depleted August-October (e.g. microbial). In addition to Cape Meares, air archive sets were analyzed from: South Pole (SPO), Samoa (SMO), Mauna Loa (MLO) 1992-1996. The presented δD measurements are unique measured values during these time periods at these stations. To obtain the long-term in isotopic CH4 from 1978-2010, other datasets of Northern Hemisphere mid-latitude sites are included with Cape Meares. These sites are Olympic Peninsula, Washington; Montaña de Oro, California; and Niwot Ridge, Colorado. The seasonal cycles of CH4 and its isotopes from the composite dataset have the same phase and amplitudes as the Cape Meares site. CH4 growth rate shows a decrease over time 1978-2010 with three main spikes in 1992, 1998, and 2003 consistent with the literature from the global trend. CH4 lifetime is estimated to 9.7 yrs. The δ13C trend in the composite data shows a slow increase from 1978-1987, a more rapid rate of change 1987-2005, and a gradual depletion during 2005-2010. The δD trend in the composite data shows a gradual increase during 1978-2001 and decrease from 2001-2005. From these results, the global CH4 emissions are estimated and show a leveling off sources 1982-2010 with two large peak anomalies in 1998 and 2003. The global average δ13C and δD of CH 4 sources are estimated from measured values. The results of these calculations indicate that there is more than one source which controls the decrease in the global CH4 trend. From 1982-2001, δ13C and δD of CH4 sources becomes more depleted due to a decrease in fossil and/or biomass burning sources relative to microbial sources. From 2005-2010, δ 13C of CH4 sources returns to its 1981 value. There are two significant peaks in δ13C and δD of CH 4 sources in 1998 and 2003 due to the wildfire emissions in boreal areas and in Europe.

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5

Wecht, Kevin James. "Quantifying Methane Emissions Using Satellite Observations." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11252.

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Methane is the second most influential anthropogenic greenhouse gas. There are large uncertainties in the magnitudes and trends of methane emissions from different source types and source regions. Satellite observations of methane offer dense spatial coverage unachievable by suborbital observations. This thesis evaluates the capabilities of using satellite observations of atmospheric methane to provide high-resolution constraints on continental scale methane emissions. In doing so, I seek to evaluate the supporting role of suborbital observations, to inform the emission inventories on which policy decisions are based, and to enable inverse modeling of the next generation of satellite observations. Earth and Planetary Sciences

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6

Butterworth, Anna Lucy. "Determination of the combined isotopic composition of atmospheric methane." Thesis, Open University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264463.

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7

Butenhoff, Christopher Lee. "Investigation of the sources and sinks of atmospheric methane." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/2813.

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The work presented here represents a number of independent studies that investigated various components of the CH4 budget, namely the sources and sinks. We used a chemical-tracer model and created unique long-term time series of atmospheric CH4, carbon monoxide (CO), molecular hydrogen (H2), and methylchloroform (CH3CCl3) measurements at marine background air to derive histories of atmospheric hydroxyl radical (OH) - the main chemical oxidant of CH4, biomass burning - an important source of CH4 in the tropics, and emissions of CH4 from rice paddies - one of the largest anthropogenic sources of CH4, over decadal scales. Globally gridded inventories of CH4 emissions from rice paddies and terrestrial vegetation were created by synthesizing greenhouse and field CH4 fluxes, satellite-derived biophysical data, and terrestrial geospatial information.

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8

Srong, E. Kimberley. "Spectral parameters of methane for remote sounding of the Jovian atmosphere." Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:0f870f86-c546-461d-aca7-61f1ccc249df.

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Spectroscopic measurements in the infrared have proven to be a valuable source of information about the Jovian atmosphere. However, numerous questions remain, many of which will be addressed by the Galileo μission, due to arrive at Jupiter in December, 1995. One of the instruments on Galileo is the Near-Infrared Mapping Spectrometer (NIMS), which will measure temperature structure, cheμical composition, and cloud properties. The objective of the work described in this thesis was to investigate the transmittance properties of the Jovian atmosphere and, in particular, to obtain transmittance functions of CH4 for future use in the planning and interpretation of NIMS measurements. This thesis begins with a review of our current understanding of the Jovian atmosphere (Chapter 1), and a description of the Galileo μission and the design and objectives of NIMS (Chapter 2). It is then shown (Chapter 3) that absorption bands of CH4 doμinate the nearinfrared spectrum of Jupiter, but that line data for CH4 are currently inadequate over much of the NIMS spectral range (0.7-5.2 /μi). For the purposes of NIMS, which has a low resolution of 0.25 /μi, the spectrum of CH4 can be characterised using band models of transmittance as a function of temperature, pressure, and abundance. The theory of band modelling is presented, and previous band-modelling studies of CH4 are reviewed and are also shown to be inadequate for NIMS (Chapter 4). An experimental investigation was therefore undertaken to record CH4 spectra under Jovian conditions of low temperature, large abundance, and H2-broadening. The experimental resources used to obtain these spectra are described (Chapter 5), the generation of the transmittance spectra is discussed, and their quality is assessed (Chapter 6). The range of frequencies and laboratory conditions covered by these spectra (listed in Appendix A) makes them one of the most comprehensive data sets of this kind yet published. These spectra were subsequently used to derive transmittance functions for CH4 (Chapter 7). A variety of models were fitted to the self-broadened CH4 spectra, and the Goody and Malkmus random band models, using the Voigt lineshape, are shown to provide the best fits. These two models were then fitted to the combined set of self- and H2-broadened CH4 spectra. The parameters fitted with the Goody-Voigt model are included in this thesis (Appendices B and C). Finally, the application of these new band model fits to the problem of Jovian remote sounding is addressed (Chapter 8). This includes an assessment of the reliability of extrapolation to Jovian conditions, a calculation of the level in the Jovian atmosphere that will be sounded by observations of CH4 absorption, and a calculation of how the uncertainties in the fitted band model will affect the retrieval of atmospheric parameters from NIMS spectra. This thesis concludes with a detailed summary, and with suggestions for future investigations which will help to maximise the return of information from NIMS.

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9

Snover, Amy Katherine. "The stable hydrogen isotopic composition of methane emitted from biomass burning and removed by oxic soils : application to the atmospheric methane budget /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11570.

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10

Bräunlich, Maya. "Study of atmospheric carbon monoxide and methane Untersuchung von atmosphärischen Kohlenmonoxid und Methan anhand von Isotopenmessungen /." [S.l. : s.n.], 2000. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8832641.

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11

Street, Rachel Anna. "Emissions of non-methane hydrocarbons from three forest ecosystems." Thesis, Lancaster University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260959.

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12

Miller, Scot M. "Emissions of Nitrous Oxide and Methane in North America." Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:17467371.

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Methane (CH_4) and nitrous oxide (N_2O) are the second- and third-most important long-lived greenhouse gas species after carbon dioxide (CO_2) in terms of radiative forcing. This thesis describes the magnitude, spatial distribution, and seasonality of N_2O and CH_4 sources over North America using atmospheric data. We also investigate the environmental drivers and/or anthropogenic source sectors that can explain these emissions patterns. Overall, this thesis provides information on the magnitude, distribution, and likely drivers of greenhouse gas emissions to aid existing or future climate change mitigation policies in the US and Canada. We estimate anthropogenic N_2O and CH_4 emissions that greatly exceed most existing inventory estimates. Our US budgets for N_2O and CH_4 are approximately 2.8 and 1.5 times higher, respectively, than inventory estimates from the US EPA. Much of the discrepancy in methane appears to stem from oil and natural gas industry and agricultural emissions. In contrast, we estimate natural CH_4 sources that are smaller than most existing process-based biogeochemical models. These estimated fluxes have a spatial distribution centered around the Hudson Bay Lowlands. Most existing models estimate fluxes that are far more spatially distributed across the Canadian shield. These estimates provide negative information on the spatial distribution of fluxes relative to a spatially-constant model. We find that a simple model using only three environmental variables can describe flux patterns (as seen by the atmospheric observations) as well as any process-based estimate. Earth and Planetary Sciences

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13

McNorton, Joe Ramu. "Analysis of recent atmospheric methane trends using models and observations." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/13294/.

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Over the past two decades the growth rate of methane has shown large variability on multi-year timescales, the reasons for which are not well understood. The JULES land surface model, TOMCAT 3-D chemical transport model and observations have been used to investigate causes for these variations, with a specific focus on wetland emissions and atmospheric loss. The role of atmospheric variability in the recent methane trends was investigated using TOMCAT, driven by variations in global mean hydroxyl concentrations derived from methyl chloroform observations. Results show that between 1999 and 2006, a stall in the atmospheric methane growth rate was, in part, caused by changes in the atmospheric loss. This was due largely to relatively small changes in global mean hydroxyl concentrations over time, with minor contributions from variations in atmospheric transport and temperature. Methane emissions from various wetland inventories were evaluated using TOMCAT and observations, and recent trends in emissions were investigated. Emissions calculated by JULES were spatially and temporally similar to a top-down emission inventory and produced good agreement with satellite observations when used in TOMCAT (R = 0.84). Emissions derived for the period 1993 – 2012 show a statistically significant (95%-level) positive trend of 0.43 Tg/yr. This suggests a long-term positive trend in wetland emissions that may continue. During the stall in methane growth (1999-2006) modelled wetland emissions were 0.4 Tg/yr lower than average. This suggests that a decrease in wetland emissions contributed to the observed stall in methane growth. The wetland methane processes within JULES were developed to include transport, oxidation, sulphate suppression, unsaturated production and methane storage pools. The parameters required for the additional processes were derived using a perturbed parameter ensemble to optimise the fit with observed fluxes. This slightly increased model performance at flux sites from R = 0.32 in the standard model to R = 0.34 in the updated model. The new version of JULES was tested using TOMCAT and satellite observations, and model agreement improved from R = 0.84 to R = 0.87, additionally the root-mean-squared-error reduced from 17.17 ppb to 15.09 ppb. This suggests the optimised additional model processes slightly improved model performance.

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14

Teama, Doaa Galal Mohammed. "A 30-Year Record of the Isotopic Composition of Atmospheric Methane." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/642.

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Methane (CH4) is one of the most important greenhouse gases after water vapor and carbon dioxide due to its high concentration and global warming potential 25 times than that of CO2 (based on a 100 year time horizon). Its atmospheric concentration has more than doubled from the preindustrial era due to anthropogenic activities such as rice cultivation, biomass burning, and fossil fuel production. However, the rate of increase of atmospheric CH4 (or the growth rate) slowed from 1980 until present. The main reason for this trend is a slowdown in the trend of CH4 sources. Measuring stable isotopes of atmospheric CH4 can constrain changes of CH4 sources. The main goal of this work is to interpret the CH4 trend from 1978-2010 in terms of its sources using measurements of CH4 mixing ratio and its isotopes. The current work presents the measurements and analysis of CH4 and its isotopes (δ13C and δD) of four air archive sample sets collected by the Oregon Graduate Institute (OGI). CH4 isotope ratios (δ13C and δD) were measured by a continuous flow isotope ratio mass spectrometer technique developed at PSU. The first set is for Cape Meares, Oregon which is the oldest and longest set and spans 1977-1999. The integrity of this sample set was evaluated by comparing between our measured CH4 mixing ratio values with those measured values by OGI and was found to be stable. Resulting CH4 seasonal cycle was evaluated from the Cape Meares data. The CH4 seasonal cycle shows a broad maximum during October-April and a minimum between July and August. The seasonal cycles of δ13C and δD have maximum values in May for δ13C and in July for δD and minimum values between September-October for δ13C and in October for δD. These results indicate a CH4 source that is more enriched January-May (e.g. biomass burning) and a source that is more depleted August-October (e.g. microbial). In addition to Cape Meares, air archive sets were analyzed from: South Pole (SPO), Samoa (SMO), Mauna Loa (MLO) 1992-1996. The presented δD measurements are unique measured values during these time periods at these stations. To obtain the long-term in isotopic CH4 from 1978-2010, other datasets of Northern Hemisphere mid-latitude sites are included with Cape Meares. These sites are Olympic Peninsula, Washington; Montaña de Oro, California; and Niwot Ridge, Colorado. The seasonal cycles of CH4 and its isotopes from the composite dataset have the same phase and amplitudes as the Cape Meares site. CH4 growth rate shows a decrease over time 1978-2010 with three main spikes in 1992, 1998, and 2003 consistent with the literature from the global trend. CH4 lifetime is estimated to 9.7 yrs. The δ13C trend in the composite data shows a slow increase from 1978-1987, a more rapid rate of change 1987-2005, and a gradual depletion during 2005-2010. The δD trend in the composite data shows a gradual increase during 1978-2001 and decrease from 2001-2005. From these results, the global CH4 emissions are estimated and show a leveling off sources 1982-2010 with two large peak anomalies in 1998 and 2003. The global average δ13C and δD of CH4 sources are estimated from measured values. The results of these calculations indicate that there is more than one source which controls the decrease in the global CH4 trend. From 1982-2001, δ13C and δD of CH4 sources becomes more depleted due to a decrease in fossil and/or biomass burning sources relative to microbial sources. From 2005-2010, δ13C of CH4 sources returns to its 1981 value. There are two significant peaks in δ13C and δD of CH4 sources in 1998 and 2003 due to the wildfire emissions in boreal areas and in Europe.

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15

Tie, XueXi. "A three-dimensional global dynamical and chemical model of methane." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/30885.

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16

Shaw, Stephanie Lyn 1973. "The production of non-methane hydrocarbons by marine plankton." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8255.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. Includes bibliographical references (p. 118-134). The oceans are a small source of non-methane hydrocarbons (NMHC), a suite of volatile organics whose chemical destruction mechanism by reaction with hydroxyl radical can significantly affect the oxidation capacity of the atmosphere. Little is known about the water column cycling processes that constrain this source; previous work has established a photochemical source for many alkenes, and a phytoplanktonic source for isoprene. The focus of this thesis was to gain further insight on marine microbiological cycling of NMHC. This included investigations on two main themes. The first was the effect of different physiological conditions on phytoplanktonic isoprene production. A variety of phytoplankton were examined for the ability to produce isoprene. All were found to have constant isoprene production rates per cell during exponential growth, with decreasing rates as the populations senesced. A positive allometric relationship between isoprene production rate and cell volume was found; highest production rates were found for the largest cell tested, Emiliania huxleyi, and lowest rates for Prochlorococcus, the smallest. Isoprene production in Prochlorococcus was found to be a function of light intensity and temperature, with patterns similar to the relationships between growth rate of this species and these environmental parameters. The second theme investigated was the effect that heterotrophic marine plankton might have on NMHC cycling. We detected no clear production or consumption of any NMHC, except isoprene, from any of the phytoplankton or other organisms tested. (cont.) The heterotrophic bacteria examined had no detectable effect on isoprene production per Prochlorococcus cell in a dual-species culture, but a temporary production of isoprene was detected from bacterial cultures grown in organically-enriched media. Nanoflagellate grazing by Cafeteria roenbergensis on Prochlorococcus had no detectable effect on NMHC cycling except to control the total phytoplankton counts, and thus total isoprene production. Besides controlling phytoplankton counts, phage lysis of Prochlorococcus had no detectable effect on NMHC cycling except to decrease isoprene production per Prochlorococcus cell during the latent period of infection. Any other effect these particular organisms may have on NMHC cycling likely involves other processes, such as photochemistry. by Stephanie Lyn Shaw. Ph.D.

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17

Barnhouse, Willard D. Jr. "Methane Plume Detection Using Passive Hyper-Spectral Remote Sensing." Bowling Green State University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1129913636.

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18

Starr, Sean Michael. "Microbial methane oxidation in the marine and estuarine environment." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313378.

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19

Santoni, Gregory Winn. "Fluxes of Atmospheric Methane Using Novel Instruments, Field Measurements, and Inverse Modeling." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:10941.

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The atmospheric concentration of methane $(CH_4)$ - the most significant non-$CO_2$ anthropogenic long-lived greenhouse gas - stabilized between 1999 and 2006 and then began to rise again. Explanations for this behavior differ but studies agree that more measurements and better modeling are needed to reliably explain the model-data discrepancies and predict future change. This dissertation focuses on measurements of $CH_4$ and inverse modeling of atmospheric $CH_4$ fluxes using field measurements at a variety of spatial scales. We first present a new fast-response instrument to measure the isotopic composition of $CH_4$ in ambient air. The instrument was used to characterize mass fluxes and isofluxes (a isotopically-weighted mass flux) from a well-studied research fen in New Hampshire. Eddy-covariance and automatic chamber techniques produced consistent estimates of both the $CH_4$ fluxes and their isotopic composition at sub-hourly resolution. We then characterize fluxes of $CH_4$ from aircraft engines using measurements made with the same instrument during the Alternative Aviation Fuel Experiment (AAFEX), a study that aimed to determine the atmospheric impacts of alternative fuel use in the growing aviation industry. Emissions of $CO_2$, $CH_4$, and $N_2O$ from different synthetic fuels were statistically indistinguishable from those of the widely used JP-8 jet fuel. We then present airborne observations of the long-lived greenhouse gas suite – $CO_2$, $CH_4$, $N_2O$, and CO – during two aircraft campaigns, HIPPO and CalNex, made using a similar instrument built specifically for the NCAR HIAPER GV aircraft. These measurements are compared to data from other onboard sensors and show excellent agreement. We discuss the details of the end-to-end calibration procedures and the data quality-assurance and quality-control (QA/QC). Lastly, we quantify a top-down estimate of California’s $CH_4$ emission inventory using the CalNex $CH_4$ observations. Observed $CH_4$ enhancements above background concentrations are simulated using a lagrangian transport model driven by validated meteorology. A priori source-specific emission inventories are optimized in a Bayesian inversion framework to show that California’s $CH_4$ budget is 1.6 ± 0.34 times larger than the current estimate of California’s Air Resources Board (CARB), the body charged with enforcing the California Global Solutions Act and tracking emission changes over time. Findings highlight large underestimates of emissions from cattle and natural gas infrastructure. Earth and Planetary Sciences

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20

Wittig, Sophie. "Estimating methane sources and sinks in the Arctic using atmospheric data assimilation." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASJ002.

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L'Arctique est une région critique pour le changement climatique. Les températures aux hautes latitudes Nord augmentent environ trois fois plus vite que la moyenne mondiale : les changements environnementaux tels que la diminution de l'étendue de la banquise ou le dégel du pergélisol progressent donc rapidement. En conséquence, des rétroactions climatiques positives sont déclenchées dans cette région, ce qui accélère encore son réchauffement. L'un de ces changements est la possible augmentation des émissions de méthane (CH4). Le CH4 est un puissant gaz à effet de serre dont la concentration moyenne mondiale dans l'atmosphère a augmenté d'environ 160 % depuis l'ère préindustrielle, une tendance qui se retrouve en Arctique. Actuellement, diverses sources de CH4, naturelles et anthropiques, contribuent aux émissions en Arctique. Les émissions anthropiques sont principalement dues à l'extraction et à la distribution de combustibles fossiles par les nations arctiques. La principale source naturelle de CH4 est constituée par les zones humides situées aux hautes latitudes Nord, mais d'autres systèmes d'eau douce, les feux de forêt, des flux géologiques et des émissions océaniques de différentes origines contribuent également au bilan de CH4 de l'Arctique. En outre, le dégel et la déstabilisation du pergélisol terrestre et sous-marin pourraient augmenter les émissions de CH4 dans un avenir proche, par exemple en raison de l'exposition de la matière organique du sol. Cependant, l'évaluation des émissions de CH4 en Arctique et de leur contribution au budget mondial reste difficile. Cela est dû, d'une part, aux difficultés à effectuer des mesures dans des zones aussi difficiles d'accès. D'autre part, de fortes variations dans la distribution spatiale des sources de méthane et une mauvaise compréhension des effets des changements en cours sur la décomposition du carbone, la végétation et l'hydrologie compliquent l'évaluation. Le but de ce travail est donc de réduire les incertitudes sur les estimations actuelles des émissions de CH4 grâce à une approche de modélisation inverse pour mieux quantifier les sources et les puits de CH4 pour les années récentes (2008 à 2019). Plus précisément, il s'agit de détecter les tendances des émissions de CH4 et les changements éventuels dans les cycles saisonniers et d'analyser la capacité du réseau d'observation in-situ actuel à caractériser les différents secteurs et les tendances futures potentiellement causées par une "bombe à méthane". La mise en œuvre de l'inversion comprend des simulations par le modèle de transport atmosphérique FLEXPART, des émissions provenant d'inventaires et de modèles biogéochimiques et des données de concentrations atmosphériques de CH4 en 42 sites d'observation dans différentes nations arctiques. Les résultats de l'inversion montrent que la majorité des sources de CH4 actuellement présentes aux hautes latitudes sont peu contraintes par le réseau d'observation existant. On ne peut donc tirer des conclusions sur les tendances et les changements dans le cycle saisonnier pour les secteurs correspondants. Seuls les flux de CH4 des zones humides sont suffisamment contraints, principalement en Amérique du Nord. Au cours de la période étudiée, les émissions des zones humides ont une légère tendance négative en Amérique du Nord et une légère tendance positive en Eurasie orientale. Dans l'ensemble, les émissions de CH4 obtenues sont inférieures aux estimations ascendantes mais supérieures aux résultats des inversions globales. La contrainte insuffisante du réseau d'observation se retrouve dans un scénario simulant des augmentations futures des émissions de CH4. Les tendances appliquées ont non seulement été détectées de manière incorrecte dans les régions où elles étaient prescrites mais encore, des émissions élevées de CH4 ont été attribuées à des zones où aucune tendance n'était présente. Un hypothétique réseau d'observation étendu ne montre que des améliorations mineures The Arctic is an especially critical region with regard to global climate change. With temperatures in high northern latitudes increasing around three times faster than the global average, changes in environmental characteristics such as declining sea ice extend or thawing permafrost soils are proceeding rapidly. As a consequence, positive climatic feedbacks are triggered in this region, whereby the Arctic warming is accelerated even further. One important impact is the high risk of increased methane (CH4) emissions. CH4 is a potent greenhouse gas whose global average concentration in the atmosphere has increased by about 160 % since pre-industrial times, a trend that is also reflected in the Arctic. Currently, various CH4 sources, both natural and anthropogenic, are contributing to CH4 emissions from the Arctic region. Anthropogenic emissions are predominantly caused by the extraction and distribution of fossil fuels by the Arctic nations. The dominant natural source of CH4 are high northern latitude wetlands; however, other freshwater systems, wildfire events, geological fluxes and oceanic emissions of different origins also contribute to the Arctic CH4 budget. Furthermore, the thawing and destabilization of terrestrial and sub-sea permafrost will potentially increase CH4 emissions in the near future, for instance by the exposure of degradable soil organic matter. However, assessing the amount of CH4 emissions in the Arctic and their contribution to the global budget still remains challenging. This is on the one hand due to the difficulties in carrying out accurate measurements in such remote areas. Besides, high variations in the spatial distribution of methane sources and a poor understanding of the effects of ongoing changes in carbon decomposition, vegetation and hydrology also complicate the assessment. Therefore, the aim of this work is to reduce uncertainties on current bottom-up estimates of CH4 emissions as well as soil oxidation by implementing an inverse modeling approach in order to better quantify CH4 sources and sinks for the most recent years (2008 to 2019). More precisely, the objective is to detect occurring trends in the CH4 emissions and potential changes in seasonal emission patterns as well as to analyze the capability of the current stationary observation network in the Arctic to constrain the different CH4 sectors and to detect possible future trends caused by a potential “methane bomb”. The implementation of the inversion included hereby footprint simulations obtained with the atmospheric transport model FLEXPART, various emission estimates from inventories and land surface models as well as data of atmospheric CH4 concentrations from 42 surface observation sites in the Arctic nations. The results of the inversion showed that the majority of the CH4 sources currently present in high northern latitudes are poorly constrained by the existing observation network. Therefore, conclusions on trends and changes in the seasonal cycle could not be obtained for the corresponding CH4 sectors. Only CH4 fluxes from wetlands are adequately constrained, predominantly in North America. Within the period under study, wetland emissions show a slight negative trend in North America and a slight positive trend in East Eurasia. Overall, the estimated CH4 emissions are lower compared to the bottom-up estimates but higher than similar results from global inversions. The insufficient constraint by the observation network is also shown by a hypothetical scenario simulating future increases in CH4 emissions. Thereby, the applied trends are not only incorrectly detected in the regions they are assigned to, but elevated CH4 emissions are also attributed to areas where no trend is given by the scenario. A hypothetical expanded observation network of stationary sites show hereby only minor improvements

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Szenasi, Barbara. "Atmospheric monitoring of the CH4 emissions at the European scale." Electronic Thesis or Diss., université Paris-Saclay, 2020. http://www.theses.fr/2020UPASJ006.

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Les concentrations atmosphériques de gaz à effet de serre ont rapidement augmenté depuis la révolution industrielle, principalement en raison des activités anthropiques. Les études menées au cours des dernières décennies ont principalement porté sur le dioxyde de carbone (CO2), qui est le principal responsable de la croissance du forçage radiatif mondial. Récemment, le méthane (CH4), deuxième contributeur le plus important, a fait l'objet d'une attention scientifique croissante car il présente un important potentiel d'atténuation. En raison de sa durée de vie relativement courte (8 à 10 ans), les efforts d'atténuation peuvent être efficaces dans des délais relativement courts. Toutefois, les estimations actuelles des émissions de CH4 à l'échelle mondiale et régionale sont très incertaines. Cette thèse vise à améliorer notre compréhension des émissions de CH4 à l'échelle européenne en abordant les différentes sources d'incertitudes.Cette thèse présente le potentiel de réduction de l'incertitude des émissions par des inversions atmosphériques descendantes des émissions de méthane. Les émissions estimées par des approches descendantes dépendent de la performance des modèles de chimie-transport (MCT) et de la précision des mesures. Le potentiel des approches descendantes dans notre cadre des émissions de CH4 en Europe est exploré par trois études, chacune se concentrant sur différentes sources d'incertitudes qui doivent être spécifiées dans les inversions atmosphériques.Dans la première étude, nous nous concentrons sur les performances de la MCT choisie en évaluant les erreurs dans la modélisation des transports et les émissions utilisées comme intrants dans la MCT. La deuxième étude cible d'autres causes possibles d'inadéquation entre les concentrations atmosphériques de CH4 mesurées et simulées, ainsi que les rapports isotopiques atmosphériques de δ13C et δ2H. Entre autres, nous analysons si les inadéquations peuvent être associées aux signatures isotopiques des sources ou aux émissions utilisées ensemble comme données d'entrée dans le modèle de transport. Ces travaux démontrent que les informations obtenues à partir de mesures isotopiques, en plus des mesures des concentrations de CH4, peuvent être utiles pour évaluer les inventaires d'émissions et estimer les émissions par inversion atmosphérique.Le potentiel des mesures de δ13C et δ2H dans les inversions atmosphériques est étudié en déterminant la précision de l'instrument nécessaire pour détecter les signaux de δ13C et δ2H provenant de diverses sources de CH4. Cette précision est examinée à l'emplacement des sites de surveillance du réseau du système intégré d'observation du carbone (ICOS). Nos résultats indiquent des exigences de haute précision pour les instruments de mesure de δ13C et δ2H. Cependant, ils révèlent que les informations isotopiques, en plus des concentrations, pourraient améliorer la discrimination des sources de CH4 lorsqu'elles sont mises en œuvre dans les inversions atmosphériques des émissions de CH4. Les travaux de cette thèse offrent des aperçus sur la manière dont les cadres d'inversion pourraient être configurés et sur les éléments essentiels pour estimer de manière fiable les émissions de CH4 à l'échelle européenne Atmospheric mixing ratios of greenhouse gases have rapidly increased since the industrial revolution, mainly due to anthropogenic activities. Studies in the past decades have primarily targeted carbon dioxide (CO2), being the largest contributor to the global radiative forcing growth. Recently, the second largest contributor, methane (CH4), has received increasing scientific attention as it has a large mitigation potential. Due to its relatively short life-time of 8-10 years, mitigation efforts can be effective within relatively short time ranges. However, current estimates of CH4 emissions at both the global and regional scales are highly uncertain. This thesis aims at improving our understanding of CH4 emissions at the European scale by addressing various sources of uncertainties.This thesis presents the potential of emission uncertainty reduction by top-down atmospheric inversions of methane emissions. Emissions estimated by top-down approaches depend on the performance of chemistry-transport models (CTMs) and the precision of measurements. The potential of top-down approaches in our framework of CH4 emissions in Europe is explored by three studies, each focusing on different sources of uncertainties that must be specified in atmospheric inversions.In the first study, we focus on the performance of the chosen CTM by assessing errors in transport modelling and emissions used as input in the CTM. The second study targets other possible causes for misfits between measured and simulated atmospheric CH4 mixing ratios, as well as isotopic ratios δ13C and δ2H. Among others, we analyse whether misfits can be associated with isotopic source signatures or emissions used together as input in the transport model. This work demonstrates that information gained from isotopic measurements, in addition to measurements of CH4 mixing ratios, can be valuable for evaluating emission inventories and estimating emissions by atmospheric inversions.The potential of δ13C and δ2H measurements in atmospheric inversions is investigated by determining the instrument precision needed to detect signals of δ13C and δ2H from various CH4 sources. This is examined at the location of monitoring sites in the Integrated Carbon Observation System (ICOS) network. Our results indicate high precision requirements on instruments measuring δ13C and δ2H. However, they reveal that isotopic information, on top of mixing ratios, could improve discrimination of CH4 sources when implemented in atmospheric inversions of CH4 emissions. The work in this thesis offers insights into how inversion frameworks could be configured and what are the essentials to reliably estimate CH4 emissions at the European scale

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Jaeger, Alexa. "Methane and carbon dioxide cycling in soils of the Harvard Forest." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/117912.

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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. Cataloged from PDF version of thesis. Includes bibliographical references (page 18). Soil is Earth's largest terrestrial carbon pool (Oertel et al., 2016) and can act as a net source of greenhouse gases (GHG). However, if organic material accumulates in soils faster than it is converted to CO2 by cellular respiration, soil becomes a smaller GHG source and even has the potential to become a GHG sink. Not much is known about factors that drive soil to be a source or a sink of GHG. Soil temperature and moisture have both been shown to correlate with CH4 emissions and temperature has been shown to correlate with CO 2 emissions (Jacinthe et al., 2015). Currently these relationships are not well constrained, particularly in upland soils, which are soils found at elevations between 100 and 500 m (Carating et al., 2014). Soil from the Harvard Forest was collected and used in two in-lab flux experiments to constrain the effect that soil moisture has on i.) the rate of CH4 and CO2 production/consumption and ii.) the fraction of injected CH4 that is oxidized to CO2 by soil microbes. The first experiment involved injecting vials containing soil samples with CH4 , taking an initial measurement with a residual gas analyzer (RGA), incubating for three days, and taking final measurements using the RGA. The results of this experiment indicated that cellular respiration is an important carbon source in these soils, with more CO2 coming from cellular respiration than from the oxidation of CH4. The second experiment involved injecting vials containing soil samples with CH4 and 14CH4 as a tracer, incubating for six days, and analyzing CO2 from each sample using a scintillation counter. This experiment showed a weak trend indicating that increased soil moisture may result in decreased CH4 oxidation. Results showed that decays per minute from the samples were lower than in a control. These results indicated that not all CO 2 from each sample was successfully captured and analyzed using the methods here. So while the trend may hold true, it should be supported by reconducting the experiment using a more reliable means of CO2 capture. The unexpected results from both experiments indicated that there is still much to be learned about the reactions that occur in these soils and how to perfect laboratory methods to study them. by Alexa Jaeger. S.B.

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Santanam, Suresh. "A trend study of atmospheric methane : 1965-81 GC and polar icecore measurements /." Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,168.

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Wilson, Christopher James. "Analysing recent spatial and temporal atmospheric methane variations using forward and inverse modelling." Thesis, University of Leeds, 2011. http://etheses.whiterose.ac.uk/3666/.

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The TOMCAT 3-D chemical transport model (CTM) has been used to investigate the cause of recent variations in global atmospheric methane (CH4), focusing on examining changes in the balance of sources and sinks of the species. The chemical loss, transport and emissions of methane have been studied and a new 4D-Var inverse version of TOMCAT has been created. The accuracy of the TOMCAT model transport was investigated by simulating the distribution of the long-lived species SF6. A range of model grid resolutions, boundary layer schemes and advection schemes were tested. New retrievals from the Atmospheric Chemistry Experiment (ACE) satellite instrument were used to test the model in the upper troposphere and lower stratosphere. The standard CTM simulated the observed distribution and growth of SF6 well. However, based on comparison with ground-based data, the interhemispheric transport in the TOMCAT model was found to be approximately 20% too slow, with too little temporal variation in southern hemisphere transport. On the whole, however, tracer transport in the CTM using its standard set-up was accurate. As a basis for the inverse model simpler advection and boundary layer (BL) schemes were tested. The advection scheme which conserved only up to first-order moments (rather than secondorder moments) did not significantly reduce the accuracy of the model transport. However, use of a local boundary layer mixing scheme rather than a non-local scheme did degrade the quality of the transport by reducing the speed of vertical mixing out of the BL. A number of currently used CH4 emission inventories were used with the forward TOMCAT model in order to examine the effect they have on the global CH4 budget, and two different estimates of the OH sink were also tested. A published OH field derived from global CH3CCl3 and a chemical box model was found to be more consistent with OH observations than the field from the full chemistry TOMCAT model. Although both OH fields produced global CH4 lifetimes consistent with published estimates, the TOMCAT OH field yielded model CH4 which was up to 100 ppb higher than observations at the surface. Data assimilation was used to improve the estimate of the stratospheric sink of CH4. Although this sink is small overall, it needs to be represented realistically in order to accurately reproduce global CH4 to within 10 ppbv. A new adjoint version of the TOMCAT model was produced by explicit coding, and was thoroughly tested. This was incorporated into a new 4D-Var inverse model which can be used to produce updated CH4 surface flux estimates which are constrained to agree with atmospheric observations. The inverse model was used to investigate emissions in the Arctic where the forward TOMCAT model and standard emissions revealed a seasonal cycle out of phase with surface CH4 observations. It was found that northern hemisphere summertime wetland emissions were overestimated in the GISS inventory by up to 100% for the period 2000-2006, and that this was likely due to the estimates of emission rates and thaw period used when producing that inventory. It was also found that increased Asian emissions suggested in the EDGAR V4.0 inventory are not consistent with observations unless mitigated by a corresponding drop in emissions elsewhere.

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Weinmann, Julian. "Influence of the Martian regolith on the atmospheric methane and water vapour cycle." Thesis, Luleå tekniska universitet, Rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75897.

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Context. The Martian methane and water cycle are subject of ongoing research through simulation. Exchange with the subsurface has a potentially strong impact, but is often neglected. Aims. For methane, I determine if adsorption with an increased enthalpy can explain the observed seasonal variations and conflicting observations by the Trace Gas Orbiter and the Curiosity rover. For water, the impact of adsorption and ice formation in the subsurface on the global cycle is studied. A new way of initializing the soil, by running a decoupled subsurface model, is tested. Depths of stable subsurface ice and subsurface water distributions are studied. Methods. A General Circulation Model (GCM) is used with a purely diffusive subsurface model. For methane, different initial states, source scenarios, and decay times are tested. For water, a model without an active atmosphere is implemented to provide an initial state. The effect of the subsurface with this initial state on the full atmospheric water cycle is tested. Results. For methane, a strong influence on the global methane cycle is observed. Seasonal variations measured at Gale Crater are reproduced, but the conflicting observations cannot be explained by adsorption. For water, the new initialization can be used without completely disrupting the water cycle. It leads to a generally wetter atmosphere, in conflict with observations. Found ice table depths do not match well with observations, but ice profiles reproduce previous findings. Conclusion. Methane adsorption is able to partly explain observed variations, but cannot be the only process to influence methane abundances. The new initialization method for water works well in principle, but a more refined model is needed for more realistic results.

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Barlow, James Mathew. "Interpretation of observed atmospheric variations of CO2 and CH4." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10507.

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The overarching theme of my thesis is understanding observed variations of northern hemisphere atmospheric carbon dioxide (CO2) and methane (CH4) concentrations. I focus my analysis on high-latitude observations of these gases, as there are large stores of carbon in boreal vegetation and tundra which are vulnerable to rapid warming in the Arctic. My thesis is split into two parts. First, I use the wavelet transform to spectrally decompose observed multi-decadal timeseries for CO2 and CH4. I perform a series of numerical experiments based on synthetic data in order to characterise the errors associated with the analysis. For CO2, I analyse the phase and amplitude of the detrended seasonal cycle of CO2 to infer changes about carbon uptake by northern vegetation. I do not find a long-term change in the length of the carbon uptake period despite significant changes in the spring and autumn phase. I do find an increase in the rate of peak uptake which coincides with the observed increase in seasonal amplitude. These results suggest that the carbon uptake period of boreal vegetation has become more intense but has not changed in length, which provides evidence for an increase in net uptake of CO2 in the high latitudes. For CH4, I test the hypothesis that an increase in Arctic wetland emissions could result in a decrease in the seasonal amplitude of CH4 in the high latitudes. This hypothesis is based on the fact that the seasonal minima of CH4 roughly coincides with the peak of high latitude wetland CH4 emissions. I find that the CH4 seasonal amplitude has significantly decreased at a number of high-latitude sites. However I also find that atmospheric transport appears to drive much of the variability in high-latitude CH4 and that transport could also be responsible for the observed changes in amplitude. I show that an increase in wetland emissions is likely to have a more pronounced effect on the high-latitude CH4 seasonal cycle in the future. In the second section of my thesis, I describe a series of experiments in collaboration with the UK Astronomy Technology Centre, in which I characterise a new instrument technology for satellite applications to observe changes in CO2 from low-Earth orbit. The proof of concepts experiments were performed with a bench top hyperspectral imager. I show that the instrument is able to capture clean spectra at the wavelengths required for CO2 with low levels of scattered light between spectra.

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Porter, William Christian. "Community Earth System Model: Implementation, Validation, and Applications." PDXScholar, 2012. https://pdxscholar.library.pdx.edu/open_access_etds/547.

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The Community Earth System Model (CESM) is a coupling of five different models which are combined to simulate the dynamic interactions between and within the Earth's atmosphere, ocean, land, land-ice, and sea-ice. In this work, the installation and testing of CESM on Portland State University's Cluster for Climate Change and Aerosol Research (CsAR) is described and documented, and two research applications of the model are performed. First, the improved treatment of cloud microphysics within recent versions of CESM's atmospheric module is applied to an examination of changes in shortwave cloud forcing (SWCF) and results are compared to output from older versions of the model. Second, the CESM model is applied to an examination of the effect that increased methane (CH4) concentrations have had on the catalytic destruction of stratospheric ozone (O3) by ozone depleting compounds (ODCs) such as chlorofluorocarbons (CFCs) and nitrous oxide (N2O).

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Reum, Friedemann [Verfasser], and Martin [Akademischer Betreuer] Claußen. "Methane emissions from the East Siberian Arctic Shelf inferred from accurate observations of atmospheric methane mole fractions / Friedemann Reum ; Betreuer: Martin Claußen." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://d-nb.info/1194547958/34.

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Reum, Friedemann Verfasser], and Martin [Akademischer Betreuer] [Claussen. "Methane emissions from the East Siberian Arctic Shelf inferred from accurate observations of atmospheric methane mole fractions / Friedemann Reum ; Betreuer: Martin Claußen." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2019. http://nbn-resolving.de/urn:nbn:de:gbv:18-99507.

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Tizzard, Louise Helen. "The Contribution to atmospheric methane from sub-seabed sources in the UK continental shelf." Thesis, University of Newcastle upon Tyne, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445613.

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Hausmann, Petra [Verfasser], and Ralf [Akademischer Betreuer] Sussmann. "Long-Term Monitoring of Atmospheric Water Vapor and Methane / Petra Hausmann ; Betreuer: Ralf Sussmann." Augsburg : Universität Augsburg, 2017. http://d-nb.info/1143518926/34.

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32

Rata, Nigel David. "Development of new cryogenic extraction techniques for studying stable isotopic ratios in atmospheric methane." Thesis, Royal Holloway, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312798.

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33

Wang, David Texan. "The geochemistry of methane isotopologues." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111690.

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Thesis: Ph.D. in Geochemistry, Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. Cataloged from student-submitted PDF version of thesis. Includes bibliographical references (pages 123-143). This thesis documents the origin, distribution, and fate of methane and several of its isotopic forms on Earth. Using observational, experimental, and theoretical approaches, I illustrate how the relative abundances of ¹²CH₄, ¹³CH₄, ¹²CH₃D, and ¹³CH₃D record the formation, transport, and breakdown of methane in selected settings. Chapter 2 reports precise determinations of ¹³CH₃D, a "clumped" isotopologue of methane, in samples collected from various settings representing many of the major sources and reservoirs of methane on Earth. The results show that the information encoded by the abundance of ¹³CH₃D enables differentiation of methane generated by microbial, thermogenic, and abiogenic processes. A strong correlation between clumped- and hydrogen-isotope signatures in microbial methane is identified and quantitatively linked to the availability of H₂ and the reversibility of microbially-mediated methanogenesis in the environment. Determination of ¹³CH₃D in combination with hydrogen-isotope ratios of methane and water provides a sensitive indicator of the extent of C-H bond equilibration, enables fingerprinting of methane-generating mechanisms, and in some cases, supplies direct constraints for locating the waters from which migrated gases were sourced. Chapter 3 applies this concept to constrain the origin of methane in hydrothermal fluids from sediment-poor vent fields hosted in mafic and ultramafic rocks on slow- and ultraslow-spreading mid-ocean ridges. The data support a hypogene model whereby methane forms abiotically within plutonic rocks of the oceanic crust at temperatures above ca. 300 °C during respeciation of magmatic volatiles, and is subsequently extracted during active, convective hydrothermal circulation. Chapter 4 presents the results of culture experiments in which methane is oxidized in the presence of O₂ by the bacterium Methylococcus capsulatus strain Bath. The results show that the clumped isotopologue abundances of partially-oxidized methane can be predicted from knowledge of ¹³C/¹²C and D/H isotope fractionation factors alone. by David Texan Wang. Ph.D. in Geochemistry

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34

Kaharabata, Samuel K. "Non-disturbing methods of estimating trace gas emissions from agricultural and forest sources." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35903.

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Two approaches, one using an atmospheric diffusion model and the other an atmospheric tracer, were used to predict the source strength of trace gases from observations of the downwind concentration field. Both approaches do not disturb the prevailing environmental and physical conditions nor the existing biogenic processes. An analytical solution to the advection-diffusion equation was used to back-calculate the source strength from the downwind concentration measurements of (i) single and multipoint (4 and 16 points) trace gas (sulphur hexafluoride (SF6) and methane (CH4)) release experiments conducted over microplots over an open field, and (ii) single point source SF6 release experiments conducted over a forested terrain. Best predictions of the source strength (to within +/-20%) were obtained from concentration observations made along the centreline of the diffusing plumes with the predictions improving when observations at the mean plume height were used. The diffusion model was then used to compute footprint estimates for neutral and unstable conditions, for tower and aircraft based observation platforms above the forest. They showed spatially constrained footprints in the surface layer, due to effective vertical coupling, so that observations from towers and low flying aircraft must be expected to be very site specific, and scaling up to larger areas will have to be done with careful consideration of surface mosaics. Above-canopy sampling of trace gases to determine volatile organic compound emissions were then interpreted in terms of footprint considerations. This was accomplished by defining the upwind canopy areas effectively sampled under the given wind and stability conditions. The analysis demonstrated, for example, that the variability observed in measured isoprene fluxes could be accounted for by varying numbers of randomly distributed clumps of emitter species within a varying footprint. It suggested that heterogeneity of the forest canopy, in ter Sulphur hexafluoride was also used as an atmospheric tracer in order to estimate CH4 emissions from manure slurry and cattle housed in barns and feedlots. (Abstract shortened by UMI.)

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Kutschera, Ellynne Marie. "Mechanisms of Methane Transport Through Trees." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/643.

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Although the dynamics of methane (CH4) emission from croplands and wetlands have been fairly well investigated, the contribution of trees to global methane emission and the mechanisms of tree transport are relatively unknown. Methane emissions from the common wetland tree species Populus trichocarpa (black cottonwood) native to the Pacific Northwest were measured under hydroponic conditions in order to separate plant transport mechanisms from the influence of soil processes. Roots were exposed to methane enriched water and canopy emissions of methane were measured using a canopy enclosure. Methane accumulation in the canopy was generally linear and the average canopy methane flux was 3.0 ± 2.6 μg CH4 min-1. Flux magnitudes from stem experiments scaled to the area of the main tree stem are comparable to whole-canopy flux values, indicating that the majority of methane emitted from the tree leaves through the stem. Samples for stable carbon isotope composition were taken during the canopy experiments. Compared to the isotopic composition of root water methane, canopy methane was depleted in 13C on average by 8.6 ± 3.3 permil; this indicates that methane moving through the tree is not following a purely bulk flow pathway (where no depletion would occur), but is instead subject to at least one fractionating mechanism. When temperature was varied, the flux at the coolest temperature was significantly different from the higher flux at the warmest temperature (p-value less than 0.02). The calculated Q10 for methane flux was 2.4, which indicates a positive feedback with temperature increase. Analysis of δ13C values of emitted CH4 in the temperature experiments shows increasing depletion with cooler temperatures and lower flux. This indicates that not only does the magnitude of flux vary with temperature, but the actual dominant transport mechanism changes as well.

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Klappenbach, Friedrich Wilhelm [Verfasser], and J. [Akademischer Betreuer] Orphal. "Mobile spectroscopic measurements of atmospheric carbon dioxide and methane / Friedrich Wilhelm Klappenbach ; Betreuer: J. Orphal." Karlsruhe : KIT-Bibliothek, 2016. http://d-nb.info/1114312576/34.

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Bubier, Jill L. "Methane flux and plant distribution in northern peatlands." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41554.

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Methane (CH$ sb4$) fluxes were measured in a range of peatland sites by a static chamber method in two regions of northern Canada, the Clay Belt of boreal Ontario and the Labrador Trough of subarctic Quebec. In both regions, seasonal mean water table position was the best predictor of mean CH$ sb4$ flux when microtopography was included in the analysis (r$ sp2$ = 0.73; p $<$ 0.01). The regression coefficients (slopes) were similar in both regions, suggesting a similar functional relationship between water table position and CH$ sb4$ flux; but the constants (intercepts) were different, implying a regional difference in climate or other biogeochemical factors. Broad-scale wetland classifications that do not account for microtopography and regional differences are inadequate for predicting CH$ sb4$ flux. Vegetation and a suite of environmental variables in both regions were analyzed with multivariate statistics. Canonical correspondence analysis (CCA) showed that hydrology (water table position) explains most of the variability in bryophyte distribution, with chemistry (pore-water pH, Ca, Mg) as the second most important factor. The relative importance of the variables is reversed for vascular species in the Clay Belt; variables correlating with bryophyte and vascular species distribution are more similar in the Labrador Trough. Hydrology and chemistry are independent variables in both regions. CH$ sb4$ flux correlated strongly with hydrology in both regions, but not with chemistry. Because of the strong correlation between bryophytes and CH$ sb4$ flux in the CCA analyses, a predictive model was developed using weighted averaging (WA) calibration. Optimum CH$ sb4$ flux values are highest for carpet/pool species and lowest for hummock species. No overlap in WA tolerances occurs between hummock and pool species, suggesting species at either end of the moisture gradient are the best predictors of CH$ sb4$ flux. Although the model works best within and not among regions, it has potential application in remote sensing of bryophytes for regional CH$ sb4$ budgets, paleoenvironmental reconstructions of CH$ sb4$ flux, and biological monitoring of future changes in CH$ sb4$ flux from climate-induced changes in peatland hydrology.

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Chen, Yu-Han 1973. "Estimation of methane and carbon dioxide surface fluxes using a 3-D global atmospheric chemical transport model." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/18068.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004. Includes bibliographical references (p. 172-180). Methane (CH₄) and carbon dioxide (CO₂) are the two most radiatively important greenhouse gases attributable to human activity. Large uncertainties in their source and sink magnitudes currently exist. We estimate global methane surface emissions between 1996 and 2001, using a top-down approach that combines observed and simulated atmospheric CH₄ concentrations. As a secondary study, we describe our participation in a CO₂ inverse-modeling intercomparison. The available methane time-series data used in this work include observations from 13 high-frequency stations (in-situ) and 74 low-frequency sites (flask). We also construct an annually-repeating reference emissions field from pre-existing datasets of individual methane processes. For our forward simulations, we use the 3-D global chemical transport model MATCH driven by NCEP meteorology. A prescribed, annually-repeating OH field scaled to fit methyl chloroform observations is used as the methane sink. A total methane source of approximately 600 Tg yr⁻¹ best reproduces the methane growth rate between 1993-2001. Using the reference emissions, MATCH can reproduce the observed methane variations at many sites. Interannual variations in transport, including those associated with ENSO and the NAO, are found to be important at certain locations. We adapt the Kalman Filter to estimate methane flux magnitudes and uncertainties between 1996 and 2001. Seven seasonal processes (3 wetland, rice, and 3 biomass burning) are optimized at each month, while three aseasonal processes (animals/waste, coal, and gas) are optimized as constant emissions. These optimized emissions represent adjustments to the reference emissions. For the entire period, the inversion reduces coal and gas emissions, and (cont.) increases rice and biomass burning emissions. The optimized seasonal emission has a strong peak in July, largely due to increased emissions from rice producing regions. The inversion also attributes the large 1998 increase in atmospheric CH₄ to global wetland emissions, consistent with a bottom-up study based on a wetland process model. The current observational network can significantly constrain northern emitting regions, but is less effective at constraining tropical emitting regions due to limited observations. We further assessed the inversion sensitivity to different observing sites and model sampling strategies. Better estimates of global OH fluctuations are also necessary to fully describe the interannual behavior of methane observations. Carbon dioxide inversions were conducted as part of the Transcom 3 (Level 1) modeling intercomparison. We further explored the sensitivity of our CO₂ inversion results to different parameters. by Yu-Han Chen. Ph.D.

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Marais, Eloise Ann. "Non-methane volatile organic compounds in Africa: a vew from space." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11313.

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Isoprene emissions affect human health, air quality, and the oxidative capacity of the atmosphere. Globally anthropogenic non-methane volatile organic compounds (NMVOC) emissions are lower than that of isoprene, but local hotspots are hazardous to human health and air quality. In Africa the tropics are a large source of isoprene, while Nigeria appears as a large contributor to regional anthropogenic NMVOC emissions. I make extensive use of space-based formaldehyde (HCHO) observations from the Ozone Monitoring Instrument (OMI) and the chemical transport model (CTM) GEOS-Chem to estimate and examine seasonality of isoprene emissions across Africa, and identify sources and air quality consequences of anthropogenic NMVOC emissions in Nigeria. Earth and Planetary Sciences

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Liu, Yuexin. "Modeling the emissions of nitrous oxide (N₂O) and methane (CH₄) from the terrestrial biosphere to the atmosphere." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/59869.

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Zubas, Laimonas. "Modelling of methane emissions utilising a Lagrangian atmospheric dispersion model in combination with Earth observation data." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/31998.

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Space-borne methane observations provide increased spatial coverage and complement the precise, but sparse network of in-situ measurement sites. In this study, a method has been developed to investigate regional-scale methane budgets using space-borne methane observations, utilising the UK Met Office Numerical Atmospheric Modelling Environment (NAME). Lagrangian atmospheric dispersion models, such as NAME, allow us to investigate fluxes at a lesser computational cost and potentially, a higher spatial resolution. An inversion algorithm was created and tested on synthetic ground measurement data. The NAME based inversion algorithm was then developed to utilise column CH4 concentrations, with an intention of applying it to Greenhouse Gases Observing SATellite (GOSAT) observations. A study utilising synthetic GOSAT-like observations was carried out, as well as synthetic inversions quantifying the performance of future methane sensing space-borne missions (CarbonSat and Sentinel-5 Precursor), when used to study fluxes over the British Isles. The results were obtained for 2 months, January and July, 2011. Sentinel-5 Precursor can reduce the flux uncertainty over England by 30% over England and Wales in July, with the remaining regions (Scotland, Republic of Ireland, Northern Ireland and northern France) achieving a reduction of 8-14%. In contrast, CarbonSat error reduction values are expected to range from 3% to 18%. Finally, we used the forward model to relate bottom-up inventories to satellite observations of atmospheric XCH4 from GOSAT. For selected regions, we have inferred patterns in atmospheric XCH4 from the spatial distribution of the surface emissions, factoring in the atmospheric transport using an atmospheric dispersion model. The forward model was found to perform poorly over Western Europe (r=0.43) and North America (r=0.48). The agreement between the observations and simulations of r=0.72 were calculated over South America, r=0.60 over South East Asia and r=0.60 over Australasia.

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Bostrom, Gregory A. "Development of a Portable Cavity Ring-Down Spectroscopic Technique for Measuring Stable Isotopes in Atmospheric Methane." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/51.

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Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.

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Sithole, Alec. "Feedbacks of Methane and Nitrous Oxide Emissions from Rice Agriculture." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/43.

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The effect of global warming on methane (CH₄) and nitrous oxide (N₂O) emissions from agriculture was investigated and simulated from a soil warming experiment. Experiments were designed and installed in a temperature controlled greenhouse. The relationships between elevated temperatures and CH₄ and N₂O emissions were determined and calculated as the Q₁₀s of production, emission and oxidation. A study of the populations of methanogens and methanotrophs at a range of soil temperatures was performed based on soil molecular DNA analysis. This study showed that global warming would increase CH₄ emissions from rice agriculture and that the resultant emissions will be potentially large enough to cause changes in the present atmospheric concentrations. This research also showed that this increase was most evident for soil temperatures below 30⁰C, above which emissions decreased with increasing temperature. The seasonal average Q₁₀s of CH₄ emission, production, oxidation, methanogen and methanotroph populations were found to be 1.7, 2.6 and 2.2, 2.6 and 3.8, respectively, over a temperature of 20-32⁰C. Considering that the processes of CH₄ production and emission are similar to those in natural wetlands, which is the largest source of atmospheric CH₄, the contribution of this feedback is likely to cause a significant increase to the present CH₄ atmospheric budget if the current global warming trend persists over the next century. The Q₁₀s of N₂O emissions and production were 0.5-3.3 and 0.4-2.9, respectively. The low Q₁₀ values found for N₂O suggest that although global warming will have a direct impact on the production and emission rates. Nevertheless, the magnitude of the impact of global on both CH₄ and N₂O emissions from agriculture is likely to vary from one region to another due to the spatial variations in agricultural soil temperatures and the likely changes in the global regional distribution of water resources (water tables, rainfall patterns), water management practices and the responses of terrestrial CH₄ and N₂O sources such as natural wetlands and plants.

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Dove, Alice E. "Methane dynamics of a northern boreal beaver pond." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23883.

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Most global and regional "greenhouse gas" budgets have neglected beaver ponds, but they have been found to be relatively high emitters of methane (CH$ sb4$) (Roulet et. al., 1992). Static chambers, bubble traps, benthic chambers. piezometers, and water column and sediment profiles were used to determine the dynamics of CH$ sb4$ production, oxidation, storage, and emissions from a northern boreal beaver pond, as part of the Boreal Forest Ecosystem-Atmosphere Study (BOREAS) from May 1 to September 15, 1994. Samples were analysed by gas chromatography, and isotopic analyses were performed by mass spectrometry. The mean flux of CH$ sb4$ from the beaver pond (155 and 320 mg CH$ sb4$ m$ sp{-2}$ d$ sp{-1}$ for vegetated and open water sites, respectively) was greater than the flux from most other northern boreal wetlands (Bubier et. al., 1995). CH$ sb4$ availability was primarily controlled by sediment temperature, and CH$ sb4$ transport was controlled by windspeed (diffusion) and atmospheric pressure (bubbles). Bubbles comprised 20 to 52% of the net annual flux comprising the remainder. A large difference in bubble flux was observed between open water (15.7 g CH$ sb4$ m$ sp{-2}$ yr$ sp{-1}$) and vegetated sites (2.9 g CH$ sb4$ m$ sp{-2}$ yr$ sp{-1}$), and isotopic analyses indicate that this difference is due, in part, to a difference in CH$ sb4$ production pathways between sites. Greater oxidation also reduced the CH$ sb4$ flux from shallow, vegetated sites. A preliminary CH$ sb4$ budget for the BOREAS northern study area indicates that beaver ponds contribute significantly (6% to 30%) to the regional CH$ sb4$ flux. The areal extent of beaver ponds needs to be determined for inclusion in regional and global CH$ sb4$ budgets.

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Gasore, Jimmy. "Quantifying emissions of carbon dioxide and methane in central and eastern Africa through high frequency measurements and inverse modeling." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115771.

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Thesis: Ph. D. in Atmospheric Sciences, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. Cataloged from PDF version of thesis. Includes bibliographical references (pages 182-189). Carbon dioxide (CO2) and methane (CH 4) are the main greenhouse gases, contributing about 81% of the total human induced radiative forcing. Sufficient observations exist to quantify the global budget of carbon dioxide and methane which is necessary for calculating the resulting radiative forcing. Still, more observations are needed to constrain their time evolution and regional budgets which are needed for climate change mitigation policies. Atmospheric observations are particularly scarce on the African continent, despite Africa's significant CO2 emissions from agriculture, biomass burning and land use changes, as well as methane emissions from wetlands. there are very few low frequency flask measurements due to limited logistics and there is no land based station at all in equatorial Africa. Satellite observations can only provide an incomplete record due to frequent clouds and aerosol in the equatorial belt. We have set up a high-frequency in-situ greenhouse gases monitoring station in North West Rwanda at Mount Mugogo. The station is intended to be a long-term station, hence, filling the gap of current lack of measurements in Equatorial Africa. The station is part of the Advanced Global Atmospheric Gases Experiment (AGAGE) and follow its calibration protocols and operational standards, therefore, providing data of internationally recognaized quality standards. We have found that massive regional scale biomass burning largely drives the bi-model seasonal cycle of carbon dioxide, carbon monoxide and black carbon with the burning following the shift of the inter-tropical convergence zone. The seasonal cycle of methane is largely driven by the inter-hemispheric gradient, where methane-rich northern hemisphere air masses are advected to the station during the northern winter. We have used the Reversible Jump Markov Chain Monte Carlo methods to estimated optimized methane and carbon dioxide emissions in the Central and East African region. We have found that the region emitted about 25 Tg of CH4 and 139 Tg of C02 in 2016. by Jimmy Gasore. Ph. D. in Atmospheric Sciences

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Ball, Tom. "Seasonal transitions in fluxes of carbon dioxide and methane from an ombrotrophic peatland, Frontenac Bog, southern Quebec." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27274.

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A climate controlled, dynamic chamber was used to measure carbon dioxide (CO$ sb2$) and methane (CH$ sb4$) exchange on an ombrotrophic peatland. The study periods were July to early November 1995, and early May to July 1996. Five sample sites, showing ecological and hydrological contrast, were investigated. Measurements of Net Ecosystem Exchange showed peak photosynthetic capacity (GP$ sb{ max})$ ranging from 0.52 $ pm$ 0.04 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to 0.03 $ pm$ 0.02 mg C m$ sp{-2}$ s$ sp{-1}$ (early November 1995). Dark respiration measurements ranged from $-$0.21 $ pm$.02 mg C m$ sp{-2}$ s$ sp{-1}$ (June 1996) to $-$0.02 $ pm$.01 mg C m$ sp{-2}$ s$ sp{-1}$ (late May 1996), and showed significant relationships to soil temperature at all sites. Site average methane measurements ranged from 29-72 mg m$ sp{-2}$ d$ sp{-1}$, and showed a strong relationship to water table on a seasonal basis, but a poor correlation to simultaneous NEE. Modelled Net Ecosystem Productivity (NEP) among sites ranged from 17.1 to 115 gC over the entire study period. The CO$ sb2$ exchanges in late spring and early fall made a large contribution to the figure due to the imbalance in the photosynthetic and dark respiration components of the carbon budget. No discernible relationship was found between seasonal NEP and methane release. The results suggest a large importance of the extreme ends of the growing season in an analysis of the carbon budget of peatlands, periods hitherto little investigated. They also suggest that NEP/methane connections may be restricted in their significance to mainly flooded mires.

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Letts, Matthew Guy. "Modelling peatland soil climate and methane flux using the Canadian Land Surface Scheme." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21590.

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A soil climate parameterization is designed for peatland environments in the Canadian Land Surface Scheme (CLASS). Three wetland soil classes account for the variation in the hydraulic characteristics of organic soils. Saturated hydraulic conductivity varies from a median of 1.0 x 10-7 m/s in deeply humidified sapric peat to 2.8 x 10-4 m/s in relatively undecomposed fibric peat. Average pore volume fraction ranges from 0.83 to 0.93. Parameters are derived for the soil moisture characteristic curves of fibric, hemic and sapric peat, using the Campbell (1974) equation employed in CLASS, and the van Genuchten (1980) formulation. Validation of modelled water table depth and peat temperature is performed for a fen in northern Quebec and a bog in north-central Minnesota. The new parameterization results in more realistic simulation than the previous version of CLASS, which was constrained to using mineral soil properties to approximate those of organic soils. Two approaches are used to model methane emissions from northern peatlands using the new soil climate parameterization in CLASS. In the first module, the multiple regression equation of Dise et al. (1993) is used to simulate daily methane emissions from water table depth and peat temperature. In the process-based module, methane flux is divided into its component parts: plant transport, diffusion and ebullition. Each of these transport mechanisms is determined by methane concentrations, which are calculated from a series of processes related to peat temperature, water table level and rooting depth. The daily methane emissions predicted by the two models are similar and correlate reasonably with observations from a bog in north-central Minnesota.

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Trudeau, M. E. "Stable isotopic analysis and firn air reconstruction of the atmospheric history of methane and delta-carbon-13." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3165813.

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Anselmo, Christophe. "Atmospheric greenhouse gases detection by optical similitude absorption spectroscopy." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1131/document.

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Cette thèse porte sur le développement théorique et expérimental d’une nouvelle méthodologie de détection des gaz à effet de serre basée sur la spectroscopie optique d’absorption. La question posée était : est-il possible d’évaluer de manière univoque la concentration d’un gaz à partir d’une mesure par spectroscopie d’absorption différentielle, dans laquelle l’étendue spectrale de la source lumineuse est plus large que celle d’une ou de plusieurs raies d'absorption de la molécule considérée et que, de plus la détection n’est pas résolue spectralement ? La réponse à cette question permettra d’entrevoir à terme le développer d’un instrument de télédétection de terrain robuste sans contrainte opto-mécanique majeure aussi bien sur la source laser que sur la chaîne de détection.Ces travaux ont donné lieu au développement d’une nouvelle méthodologie que l’on dénomme « Optical Similitude Absorption Spectroscopy » (OSAS) ou spectroscopie d’absorption optique de similitude. Cette méthodologie permet donc de déterminer de manière quantitative une concentration d’un gaz à partir de mesures d’absorption différentielle non résolue spectralement sans procédure de calibration en concentration. Ceci demande alors une connaissance précise de la densité spectrale de la source lumineuse et du système de détection. Ces travaux publiés ont permis de démontrer que cette nouvelle méthodologie est dans le domaine spectral du proche infrarouge peu sensible aux conditions thermodynamiques du gaz observé. D’autre part, ces travaux ont permis de mettre en exergue l’inversion de la Loi de Beer-Lambert non résolue spectralement ce qui donne lieu à la résolution d’un système analytique non linéaire. À cette fin le développement d’un nouvel algorithme d’inversion de ce type de mesures a pu être vérifié expérimentalement en laboratoire sur le méthane, en exploitant aussi bien des sources à large bande spectrale cohérente et non cohérente. La détection de cette molécule dans l’atmosphère a pu être réalisée dans le cadre de ces travaux en couplant judicieusement la méthodologie OSAS et la technique Lidar. Ces travaux ouvrent de nombreuses perspectives sur la détection de gaz à effet de serre dans le domaine spectral infrarouge ainsi que la possibilité de détecter plusieurs molécules d’intérêt atmosphérique simultanément This thesis concerns the theoretical and experimental development of a new methodology for greenhouse gases detection based on the optical absorption. The problem relies on the unambiguous retrieval of a gas concentration from differential absorption measurements, in which the spectral width of the light source is wider than one or several absorption lines of the considered target gas given that the detection is not spectrally resolved. This problem could lead to the development of a robust remote sensing instrument dedicated to greenhouse gas observation, without strong technology limitations on the laser source as well as on the detection system. Solving this problem, we could propose a new methodology named: "Optical Similitude Absorption Spectroscopy" (OSAS).This methodology thus allows to determine a quantitative target gas concentration from non-resolved differential absorption measurements avoiding the use of a gas concentration calibration procedure. Thereby, a precise knowledge of the emitted power spectral density of the light source and the efficiency of the detection system are needed.This work that has been recently published could demonstrate that this new methodology applied on the NIR remains accurate even in the presence of strong atmospheric pressure and temperature gradients. Moreover, we show that inverting spectrally integrated measurements which follow the Beer-Lambert law leads to solve a nonlinear system. For this, a new inversion algorithm has been developed. It was experimentally verified in laboratory on methane by using coherent and non-coherent broadband light sources. The detection of methane in the atmosphere could be also realized by coupling the OSAS methodology and the Lidar technique. Outlooks are proposed and especially on the detection of greenhouse gases in the infrared spectral domain as well as the ability to simultaneously detect several atmospheric molecules of interest

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Lysyshyn, Kathleen E. "Carbon dioxide and methane fluxes and organic carbon accumulation in old field and northern temperate forest plantation soils." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31263.

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Carbon dioxide (CO2) and methane (CH4) fluxes from the soil surface, and concentrations within the soil profile, were measured between June 1998 and Sept. 1999 at four adjacent forest plantations and an old field in Nepean, Ontario. The objectives of this study were to quantify seasonal CO2 and CH4 fluxes from the soil surface and within the soil profile to determine the effect of soil moisture and temperature, and forest age and species on the exchange, and establish a chronosequence of organic carbon accumulation in the forest plantations and the old field soils. Dynamic and static chamber techniques were used to measure surface fluxes of CO2 and CH4, respectively, and soil gas concentrations were sampled with probes. In the old field and forest plantations, surface soil CO2 flux ranged from 2.9 to 27 g CO2 m-2 d-1 and 2.0 to 39 g CO2 m -2 d-1 respectively. Significant differences due to age and species of plantation were observed. Seasonal variations in CO2 efflux from the soil surface and within the soil profile were related to variation in soil temperature and moisture. Uptake of CH4 was observed at all sites and there was no significant differences in flux due to vegetation type or age. Maximum rate of CH4 consumption was 6.3 mg CH4 m-2 d-1. Methane uptake was positively related to soil moisture conditions. The carbon content of the soil increased in all sites following the establishment of vegetation on sandy parent material. Carbon content was greatest in the upper soil profile. Rates of carbon accumulation ranged from 109 to 426 g m-2 y-1. Soil carbon increased with increasing age of plantation during the first 30 years following the establishment of vegetation on parent material, but declined as the forest plantation matured.

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Dissertations / Theses on the topic 'Atmospheric methane'

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