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At least 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

A system for measuring methane fluxes from inland and coastal wetland environments

A CH4 measuring system with a sensitivity of 0.01 ppmv and a response time of 1 sec is described. Pulses are separable from moving and stationary readings, the device floats, and air velocity in the chamber can be controlled in the range 0-4.4 m/sec. The system is set on the water so that controlled speed air from beneath can enter an inner chamber and be pumped through a gas filter correlation system (GFC) before being returned to the chamber. The GFC mechanism yields an absorption signal in the form of a dc voltage, which a processor orders printed on a strip chart as a function of time. Detection of the CH4 amounts is through IR absorption, and the sensitivity of the instrument has been measured at .002-.051 g/sq m per day with air flows in the range 0.90-4.40 m/sec. The unit can be modified to detect CO and CO2, and further applications for low plant canopies and land surfaces are indicated.

Sebacher, D. I.↗
NASA NTRS1982

Natural and anthropogenic trace gases in the southern hemisphere

The complexity of the global environment makes it necessary that many important trace gases in the earth's atmosphere be measured on a global scale before predictions can be made regarding the effects of human activities on the environment. A description is presented of measurements of 14 atmospheric trace gases in the lower atmosphere (0-4 km) of the southern hemisphere. Concentrations are considered of CCl3F, CCl2F2, CHClF2, C2.Cl3.F3, CH3CCl3, CCl4, C2.Cl4, CH3I, CHCl3, CO, CH3Cl, CH4, N2O, and OCS. The obtained data are analyzed and interpreted to statistically quantify the possible differences of concentrations in and above the boundary layer, to model the vertical profile of CH3I, and to use the data in support of previous findings that CH4 is increasing in the atmosphere.

Rasmussen, R. A.↗
NASA NTRS1982

Radiation and chemistry in the stratosphere - Sensitivity to O2 absorption cross sections in the Herzberg continuum

It is suggested that the discrepancies between observed and modeled vertical profiles of such halocarbons as CFCl3, as well as the problem of simultaneously fitting N2O, CH4, CF2Cl2 and CFCl3 profiles with a single eddy diffusion model, are due to an overestimation of the molecular oxygen absorption cross sections in the 200-220 nm spectral region. The replacement of current O2 cross sections in this range with values that are in better agreement with results for the compounds cited leads to N2O, CF2Cl2 and CFCl3 concentration reductions of factors 0.70, 0.62 and 0.19, respectively. Profiles of CH4, H2 and CO remain unchanged, and the predicted concentration of HNO3 above 30 km is reduced by about 50% for yet another improved fit with observations. It is noted that the correction proposed produces a 30% ozone increase near the 20-25 km peak.

Froidevaux, L.↗
NASA NTRS1982

Eddy diffusion at Saturn's homopause

Measurements of Saturn's He 584 A dayglow and the CH4 density profile deduced from stellar occultation data near the homopause have been combined to infer an eddy diffusion coefficient of 8 + or - 4 x 10 to the 7th sq cm/s and a temperature of 125 + 40 or - 25 K near the homopause at Voyager 2 encounter. It appears that the eddy diffusion coefficient may have increased between the Voyager encounters. Saturn's H Ly-alpha dayglow is qualitatively compatible with this increase and the interpretation of the He 584 A dayglow and CH4 absorption measurement.

Sandel, B. R.↗
NASA NTRS1982

The prebiological paleoatmosphere - Stability and composition

In the past, it was generally assumed that the early atmosphere of the earth contained appreciable quantities of methane (CH4) and ammonia (NH3). This was the type of atmosphere believed to be the most suitable environment for chemical evolution, the nonbiological formation of complex organic molecules, the precursors of living systems. Photochemical considerations suggest that a CH4-NH3 dominated early atmosphere was probably very short-lived, if it ever existed at all. Instead, an early atmosphere of carbon dioxide (CO2) and nitrogen (N2) is favored by photochemical as well as geological and geochemical considerations. Photochemical calculations also indicate that the total oxygen column density of the prebiological paleoatmosphere did not exceed 10 to the -7th of the present atmospheric level.

Levine, J. S.↗
NASA NTRS1983

New observational constraints on the temperature inversions of Uranus and Neptune

The presence of a temperature inversion in the lower stratospheres of both Uranus and Neptune is confirmed by the 20-micron photometric data presented. It is found that the brightness temperature difference between 17.8 and 19.6 microns is 0.8 + or - 0.5 K for Uranus and 1.8 + or - 0.6 K for Neptune, implying that the temperature inversions of both planets are weaker than previously thought. Comparisons with model atmospheres suggested by Appleby (1980) imply that these temperature inversions may be understood as a consequence of heating through CH4 and aerosol absorption of sunlight. The stratospheric CH4 mixing ratio of Neptune must, however, be higher than that at the temperature minimum.

Tokunaga, A. T.↗
NASA NTRS1983

Electron impact excitation of methane

A crossed molecular beam-electron beam apparatus was employed to examine the excitation cross-sections of CH4. Attention was given to 20, 30, and 200 eV impact energies at angles from 8-130 deg. Spectra were obtained in the elastic and inelastic realms as well as in the ionization continuum in the 12.99-15.0 eV energy-loss range. Differential cross-sections were also determined. The results are useful for modeling the behavior of CH4 in planetary atmospheres.

Vuskovic, L.↗
NASA NTRS1983

Sources, sinks, and seasonal cycles of atmospheric methane

It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.

Khalil, M. A. K.↗
NASA NTRS1983

NASA Global Tropospheric Experiment

The rationale and program design for the NASA Global Tropospheric Experiment (GTE) are described. The GTE is intended to characterize the global tropospheric chemistry and its interaction with the stratosphere, the land, and the ocean. The program emphasis is laid on the potential global impact of human activities, particularly those which release CH4, N2O, and chlorofluorocarbons into the atmosphere. Specific tasks defined thus far include characterizing the tropospheric gas-phase chemistry of OH, NO, and NO2, determining concentrations and distributions of CO, CH4, O3, and N2O, as well as halogens, trace metals, and reduced sulfur species. Techniques are needed for measuring the chemical fluxes between earth surface sources and sinks, the boundary layer, the free troposphere, and the stratosphere. The first phase of the GTE will be to test and develop techniques and assay the detection limits for OH, NO, and NO2 and assess the reliability of laboratory calibrations. Improvements in modelling global-scale tropospheric processes will also be pursued.

Mcneal, R. J.↗
NASA NTRS1984

Constraints on bulk composition, seasonal variation, and global dynamics of Pluto's atmosphere

The potential seasonal variation of Pluto's atmosphere is investigated by considering the behavior of the candidate atmospheric constituents Ne, N2, CO, O2, and Ar when individually mixed with CH4. The effects of diurnal and latitudinal variation of insolation and eclipses on the atmosphere are also studied. Seasonal effects are shown to dominate. It is shown that the atmospheric bulk may not be a minimum near aphelion but rather at intermediate distances from the sun during summer/winter where inadequate ice deposits may allow the atmosphere to collapse by freezing out over winter latitudes. The likely global circulation regimes for each model atmosphere are investigated as a function of temperature, and it is concluded that if CH4, O2, or CO dominates the atmosphere, Pluto will exhibit cyclic variations between an axially symmetric circulation system at perihelion and a baroclinic wave regime at aphelion. If N2 dominates the wave regime should hold continuously.

Stern, S. A.↗
NASA NTRS1984

Laser measurements of the effects of vibrational energy on the reactions of CN

Pulsed laser photolysis of C2N2 at 193 nm has been used as a source of CN radicals in both the v-double-prime = 0 and v-double-prime = 1 levels. Individual rovibronic levels of these radicals were measured as a function of time with a tunable dye laser. From these measurements the rate constants for the reaction of each of these vibrational levels with H2, O2, CO, CO2, N2, HCN, C2N2, and CH4 have been determined. Some enhancement in the rate constant with vibrational energy which could not be ascribed to quenching was observed for O2, CH4, and H2. Only vibrational quenching was observed for HCN, N2, CO2, CO and C2N2. In the CO case the vibrational quenching rate appears to be significantly enhanced by complex formation during the quenching process.

Sayah, N.↗
NASA NTRS1984

Aeronomy

From the known composition (H2, CH4, C2H2(?) at Uranus, and H2, CH4, C2H6 at Neptune) and the inversion and photolysis region temperatures, reasonable theoretical models for the upper atmospheric distribution of the neutral and ionospheric species are constructed on the basis of the expected physical and chemical processes. The models indicate that C2H2 would condense over an extensive height range of Uranus. The extent of the haze is expected to be smaller and deeper in the polar region. Some ethane is also expected to condense, mostly in the vicinity of the temperature inversion. The behavior of the acetylene condensation with latitude and time appears to be consistent with its apparent abundance variation (detected by IUE), and the brightening of Uranus observed in ground based imaging. Neptune's polar region, on the other hand is expected to be more hazy or cloudy than the equatorial region.

Atreya, S. K.↗
NASA NTRS1985

Interaction of the Magnetospheric Ions with the Surfaces of the Icy Satellites of Saturn

The extraordinary connection between the compositions of the surfaces of the satellites and ring particles and the composition of the magnetospheric plasmas in which they are embedded is examined. What may be even more exciting is this connection is being developed and understood via a combination of laboratory and satellite measurements. This interaction has stimulated new research on radiation effects in materials which will be technologically useful. Laboratory measurements have begun to characterize the changes induced in ice by ion and electron bombardment. Most attention was paid to measurements of the atoms and molecules ejected via ion bombardment, but work was initiated on changes in the spectral character of the ice. Recent results on CH4 and mixtures of HZO and CH4 indicate that a considerable amount of chemistry is induced in such ices via bombardment.

Johnson, R. E.↗
NASA NTRS1984

The spark discharge synthesis of amino acids from various hydrocarbons

The spark discharge synthesis of amino acids using an atmosphere of CH4+N2+H2O+NH3 has been investigated with variable pNH3. The amino acids produced using higher hydrocarbons (ethane, ethylene, acetylene, propane, butane, and isobutane) instead of CH4 were also investigated. There was considerable range in the absolute yields of amino acids, but the yields relative to glycine (or alpha-amino-n-butyric acid) were more uniform. The relative yields of the C3 to C6 aliphatic alpha-amino acids are nearly the same (with a few exceptions) with all the hydrocarbons. The glycine yields are more variable. The precursors to the C3-C6 aliphatic amino acids seem to be produced in the same process, which is separate from the synthesis of glycine precursors. It may be possible to use these relative yields as a signature for a spark discharge synthesis provided corrections can be made for subsequent decomposition events (e.g. in the Murchison meteorite).

Ring, D.↗
NASA NTRS1985

Compatibility of grain-stabilized platinum with candidate propellants for resistojets

Resistojets are candidates for space station auxiliary propulsion, and should be characterized by both long life and multipropellant operations, requirements limited by available materials. Grain stabilized platinum is examined for use as a resistojet thruster material. Use of platinum in other applications indicates it can be used at moderately high temperatures for extended periods of time. Past results indicate that grain-stabilized platinum should be sufficiently inert in candidate propellant environments. Therefore, compatibility of platinum-yttria (P/Y2O3) and platinum-zirconia (Pt/ZrO2) with carbon dioxide, methane, hydrogen and ammonia is examined. A series of 1000 hr tests in CO2, H2, and NH3 is conducted at 1400 C and a series of 1000 hr tests in CH4 is conducted at about 500 C. Scanning electron microscopy, Auger electron spectroscopy and depth profiling analysis are then used to determine the effects of propellants on the material surface, to evaluate possible material contamination and to evaluate grain growth. The results indicate that there is carbon deposition on the surface of the Pt/Y2O3 and Pt/ZrO2 in both the CO2 and CH4 environments. In the H2 environment, the Pt/Y2O3 and Pt/ZrO2 specimen surfaces are roughened. After exposure to the NH3 environment, the Pt/Y2O3 and Pt/ZrO2 are roughened and pitted over the entire heated area with some pitted areas along the grain boundaries. SEM photos show grain growth in cross-sectional views of all the Pt/Y2O3 samples and the Pt/ZrO2 samples, except that tested in methane. Mass loss measurements indicate that Pt/Y2O3 and Pt/ZrO2 would last in excess of 200,000 hr in each propellant environment. However, in NH3 both Pt/Y2O3 and Pt/ZrO2 are severely pitted, with voids up to 50 percent into the material. Pt/Y2O3 and Pt/ZrO2 are not recommended for high temperature service in NH3.

Whalen, M. V.↗
NASA NTRS1986

Isotopic characterisation of prebiotic synthesis of organic material

Many primitive meteorites contain an insoluble organic material, much like terrestrial kerogen, whose mode of origin is currently unknown. When sujbected to stepwise decomposition, this material, unlike its terrestrial counterpart, reveals characteristic release patterns for the stable isotopes of carbon, hydrogen and nitrogen as a function of fractional release of each element. The purpose of this study is to try to match those release patterns using organic matter synthesised in the laboratory under controlled conditions. If successful, such a study would shed light on the origin of kerogen-like organic matter in the early solar system and, by extension, on prebiotic organic synthesis in general. The range of possible syntheses, starting materials and reaction conditions to be investigated is considerable. Samples analysed to date include: a heavy oil produced by Fischer-Tropsch-type catalysis of CO + H2; a solid residue generated by a plasma discharge in CO + H2 + N2; a solid deposited on the electrodes of a Miller-Urey synthesis operating on CH4 + H2O + N2; and a solid residue formed by polymerization of light hydrocarbons procured by a Miller-Urey discharge acting on CH4. Significant structure is observed in the release patterns for the carbon and hydrogen isotopes from the synthetic samples, though there is little evidence for isotopic fractionation during the analysis itself.

Kerridge, J. F.↗
NASA NTRS1985

Physical state of volatiles on the surface of triton

Several possible configurations for volatiles on Triton are assessed. It is concluded that the simplest volatile configuration which best satisfies the constraints with the least number of ad hoc assumptions is N2 and CH4 both in solid forms, perhaps partly as a microscopic mixture, but more probably as a disequilibrium assemblage, nonuniformly distributed. Thermodynamic equilibrium is then limited by seasonal transport and the finite diffusion time of CH4 in crystalline N2. Although a nitrogen ocean cannot be excluded, it requires very restrictive assumptions.

Lunine, J. I.↗
NASA NTRS1985

Long-term changes in Saturn's troposphere

Attention is given to the results of a long term monitoring study of Saturn's H2 quadrupole and CH4 band absorptions outside the equatorial zone, over an interval of half a Saturn year that covers most of the perihelion half of Saturn's elliptical orbit (which is approximately bounded by the equinoxes). Marked long term changes are noted in the CH4 absorption, accompanied by weakly opposite changes in the H2 absorption. Seasonal changes are inferred on the basis of temporal variations in absorption. Spatial measurements have also been made in the 6450 A NH3 band since the 1980 equinox.

Trafton, L.↗