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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

High C/O Chemistry and Weak Thermal Inversion in the Extremely Irradiated Atmosphere of Exoplanet WASP-12b

The carbon-to-oxygen ratio (C/O) in a planet provides critical information about its primordial origins and subsequent evolution. A primordial C/O greater than 0.8 causes a carbide-dominated interior as opposed to the silicate-dominated composition as found on Earth; the solar C/O is 0.54. Theory, shows that high C/O leads to a diversity of carbon-rich planets that can have very different interiors and atmospheres from those in the solar system. Here we report the detection of C/O greater than or equal to 1 in a planetary atmosphere. The transiting hot Jupiter WASP-12b has a dayside atmosphere depleted in water vapour and enhanced in methane by over two orders of magnitude compared to a solar-abundance chemical equilibrium model at the expected temperatures. The observed concentrations of the prominent molecules CO, CH4, and H2O are consistent with theoretical expectations for an atmosphere with the observed C/O = 1. The C/O ratios are not known for giant planets in the solar system, although they are expected to equal the solar value. If high C/O ratios are common, then extrasolar planets are likely very different in interior composition, and formed very differently, from expectations based on solar composition, potentially explaining the large diversity in observed radii. We also find that the extremely irradiated atmosphere (greater than 2500 K) of WASP-12b lacks a prominent thermal inversion, or a stratosphere, and has very efficient day-night energy circulation. The absence of a strong thermal inversion is in stark contrast to theoretical predictions for the most highly irradiated hot-Jupiter atmospheres.

Madhusudhan, Nikku↗
NASA NTRS2003

Validation of the Measurement of Pollution in the Troposphere (MOPITT) Experiment by Ground-Based Infrared Solar Spectroscopic Measurements of Carbon Monoxide (CO) and Methane (CH4)

The goal of the MOPITT experiment is to enhance our knowledge of the lower atmosphere system and particularly how it interacts with the surface/ocean/biomass systems. The particular focus is the distribution, transport, sources and sinks of carbon monoxide and methane in the troposphere. The MOPITT instrument was launched on EOS TERRA satellite December 18, 1999. After the launch and until March 22, 2000 the MOPITT instrument was in engineering and calibration mode. Beginning March 23, 2000 through May 6, 2001 the instrument was in a science measurement mode with some calibration breaks. On May 7, 2001 a criocooler on a side B died and channels 1 - 4 became inoperational. The MOPITT resumed its scientific measurements on August 25, 2001 with channels 5 - 8. With some calibration breaks the instrument currently provides the data. The project has three elements to it: hardware, data analysis and modeling. The MOPITT instrument, on the NASA EOS Terra satellite, measures the upwelling infrared radiance. Using the technique of correlation spectroscopy, information regarding the distribution of atmospheric CO and CH4 can be extracted. By using appropriate data analysis techniques, concentration profiles of CO are currently obtained on a global basis at a reasonably high horizontal (approximately 22km) and vertical resolution (approximately 3km). Column amounts of methane will be derived over the sunlit side of the orbit. These profiles are assimilated into models to study the chemistry and dynamics of CO, CH4 and other constituents of the lower atmosphere.

Pougatchev, Nikita↗
DOE OSTI2023

Selective Formation of Acetic Acid and Methanol by Direct Methane Oxidation Using Rhodium Single-Atom Catalysts

Atomically dispersed catalysts such as single-atom catalysts have been shown to be effective in selectively oxidizing methane, promising a direct synthetic route to value-added oxygenates such as acetic acid or methanol. However, an important challenge of this approach has been that the loading of active sites by single-atom catalysts is low, leading to a low overall yield of the products. We report an approach that can address this issue. It utilizes a metal–organic framework built with porphyrin as the linker, which provides high concentrations of binding sites to support atomically dispersed rhodium. It is shown that up to 5 wt% rhodium loading can be achieved with excellent dispersity. When used for acetic acid synthesis by methane oxidation, a new benchmark performance of 23.62 mmol·gcat –1 ·h –1 was measured. Furthermore, the catalyst exhibits a unique sensitivity to light, producing acetic acid (under illumination, up to 66.4% selectivity) or methanol (in the dark, up to 65.0% selectivity) under otherwise identical reaction conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Atmospheric methane /CH4/ - Trends and seasonal cycles

On the basis of 22 months of almost continuous automated, GC/FID measurements of atmospheric CH4 and Cape Meares (45 deg N), it is shown that the concentration of CH4 is increasing at about 2% per yr (+ or - 0.5%/yr). The data also revealed stable seasonal cycles with peak concentrations in October and minimum concentrations in July. The magnitude of the seasonal variations during these months is about + or - 20 ppby from the average (+ or - 1.2%). If the current trend continues, the increased CH4 concentration may result in a 0.2 K to 0.4 K average increase in earth's surface temperature over the next 40 years or so (based on calculations of Wang et al. (1976)). The coupling of CH4 to tropospheric and stratospheric chemical processes is discussed.

Rasmussen, R. A.↗
NASA NTRS1992

Photochemical model for NH3 in an early Martian atmosphere

A warm and wet climate scenario for early Mars has been explained by invoking a 5-bar CO2 atmosphere; however, Kasting has shown that CO2 will condense in the Martian atmosphere at these pressures. The formation of CO2 clouds will reduce the convection lapse rate and reduce the magnitude of the greenhouse effect. It is possible that additional greenhouse gases such as methane and ammonia were present in the early Mars atmosphere. We are using a one dimensional photochemical model to estimate the magnitude of the ammonia source required to maintain a given ammonia concentration in a dense CO2 atmosphere. Because CO2 is 2.5 times more efficient at Rayleigh scattering than Earth's N2 atmosphere, we anticipate increased scattering opacities and decreased photolytic destruction rates of ammonia on early Mars. The reduced gravity on Mars means that a 1 bar atmosphere will be approximately 3 times as thick as on Earth. It is possible that ammonia could have been shielded from photolysis by hydrocarbon aerosols which form as a product of methane photolysis.

Brown, L. L.↗
DOE OSTI2021

On the Viability of Video Imaging in Leak Rate Quantification: A Theoretical Error Analysis

Optical gas imaging through multispectral cameras is a promising technique for mitigation of methane emissions through localization and quantification of emissions sources. While more advanced cameras developed in recent years have led to lower uncertainties in measuring gas concentrations, a systematic analysis of the uncertainties associated with leak rate estimation have been overlooked. We present a systematic categorization of the involved uncertainties with a focus on a theoretical analysis of projection uncertainties that are inherent to this technique. The projection uncertainties are then quantified using Large Eddy Simulation experiments of a point source release into the atmosphere. Our results show that while projection uncertainties are typically about 5% of the emission rate, low acquisition times and observation of the gas plume at small distances from the emission source (<10 m) can amount to errors of about 20%. Further, we found that acquisition times on the order of tens of seconds are sufficient to significantly reduce (>50%) the projection uncertainties. These findings suggest robust procedures on how to reduce projection uncertainties, however, a balance between other sources of uncertainty due to operational conditions and the employed instrumentation are required to outline more practical guidelines.

47 OTHER INSTRUMENTATION↗
NASA NTRS1991

Global biomass burning - Atmospheric, climatic, and biospheric implications

On a global scale, the total biomass consumed by annual burning is about 8680 million tons of dry material; the estimated total biomass consumed by the burning of savanna grasslands, at 3690 million tons/year, exceeds all other biomass burning (BMB) components. These components encompass agricultural wastes burning, forest burning, and fuel wood burning. BMB is not restricted to the tropics, and is largely anthropogenic. Satellite measurements indicate significantly increased tropospheric concentrations of CO and ozone associated with BMB. BMB significantly enhances the microbial production and emission of NO(x) from soils, and of methane from wetlands.

Levine, Joel S.↗
DOE OSTI2020

Production of liquids and reduced sulfur gaseous products from sour natural gas

Aspects of the invention are associated with the discovery of approaches for the conversion of sour natural gas streams, by conversion to liquid hydrocarbons. Particular processes and their associated apparatuses advantageously combine (i) dehydroaromatization (DHA) of methane in a gaseous feedstock, to produce aromatic hydrocarbons such as benzene, with (ii) the reaction of H2S and methane in this feedstock, to produce organic sulfur compounds such as carbon disulfide (CS2) and thiophene (C4H4S). A gaseous product having a reduced concentration of H2S is thereby generated. The aromatic hydrocarbons and organic sulfur compounds may be recovered in a liquid product. Both the gaseous and liquid products may be easily amenable to further upgrading. Other advantages of the disclosed processes and apparatuses reside in their simplicity, whereby the associated streams, including a potential gaseous recycle, generally avoid high partial pressures of H2S.

03 NATURAL GAS↗
NASA NTRS1980

Response of the global climate to changes in atmospheric chemical composition due to fossil fuel burning

Tropospheric ozone and methane might increase in the future as the result of increasing anthropogenic emissions of CO, NOx and CH4 due to fossil fuel burning. Since O3 and CH4 are both greenhouse gases, increases in their concentrations could augment global warming due to larger future amounts of atmospheric CO2. To test this possible climatic impact, a zonal energy-balance climate model has been combined with a vertically-averaged tropospheric chemical model. The latter model includes all relevant chemical reactions which affect species derived from H2O, O2, CH4 and NOx. The climate model correspondingly incorporates changes in the infrared heating of the surface-troposphere system resulting from chemically induced changes in tropospheric ozone and methane. This coupled climate-chemical model indicates that global climate is sensitive to changes in emissions of CO, NOx and CH4, and that future increases in these emissions could enhance global warming due to increasing atmospheric CO2.

Cess, R. D.↗
DOE OSTI2022

Olefin methylation over iron zeolites and the methanol to hydrocarbons reaction

The effect of olefin addition to a stream of dimethyl ether on the methanol homologation reaction is investigated using iron-substituted zeolites Fe-beta and Fe-ZSM-5. The reaction was investigated using plug-flow microreactors in the temperature range of 240–400 °C, at a total pressure of 0.239 MPa and a WHSV of 6.12 (g DME/ gcat -hr). For Fe-beta (Si/Fe= 9.2) catalysts, isobutene co-feeding almost doubles dimethyl ether (DME) consumption rate and shifts selectivity towards larger olefins with carbon numbers from 5 to 7. Addition of isobutene above 6.3%, however, resulted in a reduction of DME consumption rates, an effect assigned to the replacement of surface methoxy groups for adsorbed olefins in the zeolite pores. Below a temperature of 340 °C hydride-transfer rates are negligible; reaction rates are stable for over 5.5 h and the products consist almost exclusively of olefins and a small amount of methane. Above 360 °C the onset of catalytic hydride transfer processes is observed leading to fast catalyst deactivation rates and an increase in the concentration of aromatic species. Iron ZSM-5 (Si/Fe = 21.4) catalysts under similar reaction conditions consumes methanol faster than Fe-beta at approximately three times the TOF (on a per iron basis). The Fe-ZSM-5 catalyst was selective to a distribution of products (C5 to C8) as compared to Fe-beta which was selective to primarily C5 and C7. Co-feeding larger olefins (2-methyl-2-butene, 2,3-dimethyl-2-butene, 2,3,3-trimethyl-1-butene, and 2,4,4-trimethyl-2-pentene) at a 3.9% olefin concentration over Fe-beta changed selectivity towards cracking products (C4 compounds such as isobutene). As the size of the olefin increases, a reduction of DME consumption rate is also observed. Here these results show that co-feeding olefins with DME over Fe-zeolites is a promising route to increase methylation rates at relatively low temperatures producing larger branched olefins and that the product distribution is highly dependent on the zeolite pore size and structure of the olefin.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Improved sampling technique to collect natural gas from hydrate-bearing pressure cores

High quality gas compositional data are an important factor in interpreting the genetic source of natural gas hosted in hydrate-bearing sediments and other subsurface systems. In order to accurately characterize the composition of gas samples degassed from hydrate-bearing pressure cores, one must use a reproducible sampling technique that minimizes artifacts of the sampling process. Herein, we review sediment core degassing techniques and compare data obtained from a commonly used degassing approach, which we term the standard quantitative degassing (SQD) technique, to our newly developed modified quantitative degassing (MQD) method designed to minimize atmospheric contamination and gas-water interactions. The SQD method allows sample gas to interact with water in a bubbling chamber, which we hypothesize could alter the gas composition following mixing with water or dissolved gases in the bubbling chamber. Whereas, the MQD method allows for the collection of sample gas prior to the bubbling chamber. To compare the SQD and MQD methods, we performed a side-by-side comparison of noble (He, Ne, Ar, Kr, and Xe), major (H 2 , N 2 , O 2 , and CO 2 ), and hydrocarbon (CH 4 , C 2 H 6 , C 3 H 8 , i-C 4 H 10 , C 4 H 10 , i-C 5 H 12 , C 5 H 12 ) gas concentrations and select isotopic compositions obtained using both sample collection techniques. Gas samples were collected from hydrate-bearing pressure cores recovered and maintained under hydrate stable conditions from the northern Gulf of Mexico during the UT-GOM 2 -1 Expedition. The MQD method displayed significantly lower concentrations of atmospheric gases, higher proportions of hydrocarbon gases, lower ratios of C 1 /C 2 + , and heavier stable carbon and hydrogen isotopes of methane than the SQD method. These results demonstrate that the MQD method reduced air contamination and minimized alteration of the hydrocarbon gases. Finally, we conclude this method may be important for future work that seeks to determine the composition of natural gas from pressure cores using quantitative degassing experiments, especially those seeking to measure major (e.g., N 2 ) and noble gases.

58 GEOSCIENCES↗
NASA NTRS2010

Seven Years of Observations of Mid-Tropospheric CO2 from the Atmospheric Infrared Sounder

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002. AIRS acquires hyperspectral infrared radiances in the 3.7-15.4 um spectral region with spectral resolution of better than 1200. The AIRS was designed to measure temperature and water vapor profiles and cloud properties for improvement in weather forecast and improved parameterization of climate processes. Currently the AIRS Level 1B Radiance Products are assimilated by NWP centers and have shown considerable forecast improvement. Scientists have also demonstrated accurate retrievals of minor gases from AIRS including Carbon Monoxide, Methane, and Ozone. The excellent sensitivity and stability of the AIRS instrument has recently allowed the AIRS team to successfully retrieve Carbon Dioxide (CO2) concentrations in the mid-troposphere (8-10 km) with a horizontal resolution of 100 km and accuracy of 1-2 ppm. The AIRS retrieves over 15,000 measurements per day and can achieve full global coverage in 30 days. The AIRS CO2 accuracy has been validated against a variety of aircraft measurements in the mid-troposphere and upward looking interferometers. Findings from the AIRS data include higher than expected variability in the mid-troposphere, the presence of a belt of CO2 in the southern hemisphere, and numerous observations of atmospheric circulation including the effects of El Nino/La Nina on the CO2 concentrations in the mid-troposphere. The full mid-tropospheric AIRS CO2 data set is now available at the NASA GES/DISC for almost eight years since AIRS has been operational.

carbon dioxide↗
DOE OSTI2022

Observed Relationships Between Cloud Droplet Effective Radius and Biogenic Gas Concentrations in Summertime Marine Stratocumulus Over the Eastern North Atlantic

Abstract Biogenic gases are a prominent component of the summertime marine boundary layer (MBL) over the Eastern North Atlantic. One of these gases, dimethyl sulfide (DMS), can produce sulfate cloud condensation nuclei (CCN) that, in theory, can brighten clouds through photolysis, and produces a reaction product, methane sulfonic acid (MSA). It is also possible that DMS can interact with sea‐salt or other marine aerosols changing their CCN activation spectrum, which could also modify cloud microphysical structure. Data collected aboard the G1 aircraft during the Aerosol Cloud Experiment Eastern North Atlantic (ACE‐ENA) in well‐mixed and decoupled marine boundary layers (MBLs) were used to examine relationships between the cloud droplet effective radii, , and the concentrations of DMS and MSA in constant cloud liquid water content (LWC) bins. A weak but statistically significant negative correlation was observed between CCN concentration and in most LWC bins, regardless of the source of the CCN, while a weak but statistically significant positive correlation between and DMS was observed. No correlation between the cloud droplet number concentration and DMS was found. The presence of MSA indicated that DMS‐to‐sulfate photolysis was likely occurring, but data sparsity prevented a statistically significant conclusion regarding the relationship between MSA and . Data sparsity in decoupled conditions also prevented statistically significant conclusions. To properly address biogenic gas impacts on cloud microphysics, it is recommended that aircraft data be supplemented by long‐term biogenic gas measurements at the surface in marine locations with appropriate remote and in‐situ cloud sensing capabilities, and the analysis limited to well‐mixed MBL's.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

SPRUCE Sphagnum Phytobiome Responses to Whole Ecosystem Warming and Elevated Atmospheric CO2 in July, 2017-2021

This dataset reports the carbon (C) and nitrogen (N) isotopic composition of Sphagnum moss tissue collected from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site within the Marcell Experimental Forest in northern Minnesota, USA. Tissues were collected inside the SPRUCE experimental study plot, where air and peat warming are combined in whole-ecosystem warming treatments, from 2019-2021. Additionally, rates of nitrogen fixation and methane oxidation measured for Sphagnum from 2017, 2019, and 2021. Sphagnum tissue % water content was measured at all timepoints. This dataset was used to conduct analyses within Petro et al (2023). Sphagnum C and N concentrations and 13C and 15N isotopic natural abundance were determined for three replicate Sphagnum tissue samples collected from inside the SPRUCE enclosures in July 2019-2021. Elemental and isotope analyses were conducted at the University of Georgia – Center for Applied Isotope Studies (CAIS; https://cais.uga.edu/). Plant elemental analysis was performed by the micro-Dumas method, while isotopic natural abundance was measured by isotope ratio mass spectrometry. 13C natural abundance is expressed as the per mille (‰) deviation from the Pee Dee Belemnite standard (PDB) 13C:12C ratio (δ13C), while 15N natural abundance is expressed as the ‰ deviation from the N2 atmospheric 15N:14N ratio (δ15N). Rates of nitrogen fixation and methane oxidation were measured using serum bottle incubations performed with Sphagnum collected inside the SPRUCE enclosures in July 2017, 2019, and 2021. Rates were calculated according to the amount of 15N-N2 or 13C-CH4 (methane) incorporated into the Sphagnum tissue or incubation headspace over the 48-hour intion period. In 2017, incubations were performed in growth chambers set to the temperature of the experimental plots during Sphagnum sampling. In 2019 and 2021, the incubations were performed directly inside the experimental plots. The 13C and 15N isotopic natural abundance data and rate measurements presented in this dataset provide insight into the impacts of whole-ecosystem warming and elevated atmospheric carbon dioxide (CO2) on N and C cycling within the Sphagnum phytobiome. This dataset contains two data files in comma-separate values (*.csv) format. Additional metadata are provided: two data dictionaries and a file-level metadata file in comma-separate values (.csv) format and a user guide in PDF (*.pdf) format. Additional datasets on NH4-N availability, porewater concentrations of CH4 and CO2, and Sphagnum groundcover within the SPRUCE experimental plots are available. These are outlined in the Related Datasets section in the user guide.

delta 13 carbon↗
NASA NTRS1977

Possible variations in atmospheric methane

A model coupling photochemistry and vertical transport in the troposphere has been used to investigate the magnitude of possible future perturbations to atmospheric CH4. The response of atmospheric CH4 to an increase in the concentration of CO or to a variation in stratospheric O3 is studied. Both of the above mechanisms, which could be caused by man's activities, arise because a change in the concentration of tropospheric OH will lead to a change in the CH4 abundance. The calculations imply that a perturbation of about 30-40% in atmospheric CH4 could occur if stratospheric O3 were perturbed by 10% or if man-made CO continued to increase. The possible consequences of a CH4 perturbation may entail a perturbation in stratospheric photochemistry or in the thermal balance of the atmosphere.

Chameides, W. L.↗
DOE OSTI2021

Surface characterization and methane activation on SnO x /Cu 2 O/Cu(111) inverse oxide/metal catalysts

To activate methane at low or medium temperatures is a difficult task and a pre-requisite for the conversion of this light alkane into high value chemicals. In this work, we report the preparation and characterizations of novel SnO x /Cu 2 O/Cu(111) interfaces that enable low-temperature methane activation. Scanning tunneling microscopy identified small, well-dispersed SnO x nanoclusters on the Cu 2 O/Cu(111) substrate with an average size of 8 Å, and such morphology was sustained up to 450 K in UHV annealing. Ambient pressure X-ray photoelectron spectroscopy showed that hydrocarbon species (CH x groups), the product of methane activation, were formed on SnO x /Cu 2 O/Cu(111) at a temperature as low as 300 K. An essential role of the SnO x –Cu 2 O interface was evinced by the SnO x coverage dependence. Systems with a small amount of tin oxide, 0.1–0.2 ML coverage, produced the highest concentration of adsorbed CH x groups. Calculations based on density functional theory showed a drastic reduction in the activation barrier for C–H bond cleavage when going from Cu 2 O/Cu(111) to SnO x /Cu 2 O/Cu(111). On the supported SnO x , the dissociation of methane was highly exothermic (ΔE ~ –35 kcal mol –1 ) and the calculated barrier for activation (~20 kcal mol –1 ) could be overcome at 300–500 K, target temperatures for the conversion of methane to high value chemicals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Understanding the Impact of Hydrogen Activation by SrCe 0.8 Zr 0.2 O 3-δ Perovskite Membrane Material on Direct Non-Oxidative Methane Conversion

Direct non-oxidative methane conversion (DNMC) converts methane (CH 4 ) in one step to olefin and aromatic hydrocarbons and hydrogen (H 2 ) co-product. Membrane reactors comprising methane activation catalysts and H 2 -permeable membranes can enhance methane conversion by in situ H 2 removal via Le Chatelier's principle. Rigorous description of H 2 kinetic effects on both membrane and catalyst materials in the membrane reactor, however, has been rarely studied. In this work, we report the impact of hydrogen activation by hydrogen-permeable SrCe 0.8 Zr 0.2 O 3-δ (SCZO) perovskite oxide material on DNMC over an iron/silica catalyst. The SCZO oxide has mixed ionic and electronic conductivity and is capable of H 2 activation into protons and electrons for H 2 permeation. In the fixed-bed reactor packed with a mixture of SCZO oxide and iron/silica catalyst, stable and high methane conversion and low coke selectivity in DNMC was achieved by co-feeding of H 2 in methane stream. The characterizations show that SCZO activates H 2 to favor “soft coke” formation on the catalyst. The SCZO could absorb H 2 in situ to lower its local concentration to mitigate the reverse reaction of DNMC in the tested conditions. The co-existence of H 2 co-feed, SCZO oxide, and DNMC catalyst in the present study mimics the conditions of DNMC in the H 2 -permeable SCZO membrane reactor. The findings in this work offer the mechanistic understanding of and guidance for the design of H 2 -permeable membrane reactors for DNMC and other alkane dehydrogenation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗