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At least 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Evidence for weather on Neptune. I

Between April 1975 and March 1976 the reflectance of Neptune between 1 and 4 microns increased substantially. A spectrum taken at these wavelengths near the period of peak observed brightness showed a low-intensity continuum with weak superposed absorptions caused by CH4 and H2. Photographic spectra of the planet measured during the same period showed no differences from older published data. The gas abundances derived from the infrared spectrum, 5 plus or minus 2 km-amagat of H2 at a base density of 0.26 plus or minus 0.08 am and no more than about 1 m-am of CH4, appear to refer to an effective reflecting level high in the atmosphere of Neptune.

Joyce, R. R.↗
NASA NTRS1977

Investigation of the formation of gaseous sodium sulfate in a doped methane-oxygen flame

Na2SO4(g) formation was measured at atmospheric pressure in CH4-O2 flames, with high pressure, free-jet expansion, mass spectrometric sampling used to identify and measure reaction products. Measured composition profiles of reaction products for a doped 9.5 mole ratio O2/CH4 flame are presented. Weight percentages of reactants were 4.7 CH4, 89.0 O2, 3.5 H2O, 2.0 SO2 and 0.35 NaCl.

Stearns, C. A.↗
NASA NTRS1977

Sources and sinks for atmospheric H2 - A current analysis with projections for the influence of anthropogenic activity

Oxidation of CH4 provides the major source for atmospheric H2, which is removed mainly by reaction with OH. Biological activity at earth's surface appears to represent at most a minor sink for H2. Anthropogenic activity is a significant source for both H2 and CO in the present atmosphere and may be expected to exert a growing influence in the future. Models are presented which suggest a rise in the mixing ratio of H2 from its present value of 5.6 ten-millionths to about 1.8 millionths by the year 2100. The mixing ratio of CO should grow from 9.7 hundred-millionths to 2.3 ten-millionths over the same time period, and there should be a rise in CH4 by about a factor of 1.5 associated with anthropogenically induced reductions in tropospheric OH.

Penner, J. E.↗
NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO was determined by the flash-photolysis resonance fluorescence method to be 7.5 plus or minus 0.9 (2 sigma) times 10 to the minus 11th power cu cm/molecule sec at 298 K and to have a negligible temperature dependence. This rate which is more than 2000 times faster than the rate of Cl + CH4 indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratosphere ozone than previously believed. Ambient stratospheric ozone will depend less on the ambient chlorine amount and the predicted response to chlorine perturbations will be lessened. One-dimensional eddy-diffusion photochemical model calculations indicate a factor of 1.1 less sensitivity to chlorine than recently reported. For a steady-state CFM release at 1975 rates (750,000 tons/year) the eventual ozone depletion is now calculated to be 14%.

Stief, L. J.↗
NASA NTRS1978

Limb brightening on Uranus - An interpretation of the lambda 7300 A methane band

Measurements of limb brightening on the Uranus disk within the lambda 7300 A CH4 band are interpreted using an elementary inhomogeneous radiative transfer model to describe the atmosphere. A two layer model which consists of a finite, optically thin, region of conservatively scattering particles overlying a semi-infinite clear H2-CH4 atmosphere satisfactorily explains the observations. The maximum optical thickness of the upper layer appears to lie in the range 0.1 to 0.2. The CH4/H2 mixing ratio in the lower layer is larger than the corresponding solar value by a factor on the order of three or greater. The results are discussed briefly in terms of current models of the Uranus atmosphere.

Price, M. J.↗
NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO has been determined by the flash-photolysis-resonance fluorescence method to be + or - 0.9 (2 sigma) x 10 to the -11th power cu cm/molecule per sec at 298 K and to have a negligible temperature dependence. This rate, which at stratospheric temperatures is more than 2000 times faster than the rate of Cl + CH4 and more than a factor of 2 faster than Cl + HO2, indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) and HO2 for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratospheric ozone than previously believed. One-dimensional eddy-diffusion photochemical model calculations indicate that the eventual ozone depletion for a steady-state chlorfluoromethane release at 1975 rates (750,000 tons/year) will be lowered from 20% to 18.5% by the inclusion of this reaction.

Stief, L. J.↗
NASA NTRS1978

The effect of anthropogenic carbon monoxide on the methane budget of the troposphere

Photochemical model calculations indicate that significant perturbations in tropospheric OH, CH4, and related compounds may occur in the coming decades due to increased anthropogenic emissions of CO and NO(x). The magnitude and direction of the perturbation depends on future emission rates of CO and NO(x) and also on the efficiency with which urban NO(x) is transported to the ambient atmosphere. If CO and NO(x) emissions increase at comparable rates, the CO effect on OH will dominate and OH will decrease while CH4 increases. The effects of a variation in tropospheric OH, halocarbons, and other compounds include a perturbation to stratospheric ozone and the atmosphere's thermal equilibrium.

Chameides, W. L.↗
NASA NTRS1978

A gas filter correlation analyzer for methane

A fast-response instrument for monitoring CH4 was designed and tested using a modified nondispersive infrared technique. An analysis of the single-beam rotating-cell system is presented along with the signal processing circuit. A calibration of the instrument shows that the technique can be used to measure CH4 concentrations as small as 5 ppm-m and the effects of interfering gases are analyzed.

Sebacher, D. I.↗
NASA NTRS1979

Experimental and theoretical examples of the value and limitations of transition state theory

Value and limitations of transition-state theory (TST) are reviewed. TST analyses of the temperature dependence of the 'direct' reactions CH3 + CH3CHO yields CH4 + CH3CO(1) and O + CH4 yields OH + CH3(2) are presented in detail, and other examples of TST usefulness are recalled. Limitations are discussed for bimolecular processes in terms of 'complex' vs. 'direct' mechanisms. The reaction OH + CO yields CO2 + H is discussed in this context. Limitations for unimolecular processes seem to arise only for simple bond fission processes, and recent advances are noted.

Golden, D. M.↗
NASA NTRS1979

Uranus - Narrow-waveband disk profiles in the spectral region 6000 to 8500 Angstroms

New narrow-band (100 A) photoelectric slit scan photometry of Uranus has been obtained in the spectral region 6000 to 8500 A. Coarse radial intensity profiles in seven wavebands are presented. Results of the investigation confirm earlier studies of limb brightening on the Uranus disk, but not all strong CH4 absorption bands are found to exhibit limb brightening. Specifically, the CH4 bands at 8000 and 8500 A show pronounced apparent limb darkening. Polar brightening may be responsible for the phenomenon. If so, an aerosol haze with a local optical thickness of approximately 0.5 or greater would be required. Visibility of the dense cloud layer located deep in the atmosphere might also cause apparent limb darkening. If so, the maximum permitted CH4/H2 mixing ratio in the visible atmosphere would correspond to 3 times the solar value.

Price, M. J.↗
NASA NTRS1979

Jupiter's atmospheric composition and cloud structure deduced from absorption bands in reflected sunlight

The spectrum of sunlight reflected by Jupiter is analyzed by comparing observations of Woodman (1979) with multiple-scattering computations. The analysis yields information on the vertical cloud structure at several latitudes and on the abundance of CH4 and NH3 in the atmosphere of Jupiter. The abundances of CH4 and NH3 suggest that all ices and rocks are overabundant on Jupiter by a factor of 2 or more, providing an important constraint on models for the formation of Jupiter from the primitive solar nebula. The pressure level of the clouds, the gaseous NH3 abundance, the mean temperature profile, and the Clausius-Clapeyron relation suggest that these clouds are predominantly ammonia crystals with the cloud bottom at 600-700 mb. A diffuse distribution of aerosols exists between 150 and 500 mb, and the spectral variation of albedo reflects a changing bulk absorption coefficient of the material composing the aerosols and is diagnostic of the aerosol composition.

Sato, M.↗
NASA NTRS1979

Evaluation of atmospheric trace constituent sensors operating from remote space and airborne platforms

A laboratory gas analysis system was developed specifically to make trace level measurements of carbon monoxide. To assure that the data collected with this system are correctly aligned with other established methods for making these measurements, an intercalibration study was conducted. The calibration gas was analyzed by the various participating laboratories and found to contain 1.28 ppm CO. Samples were collected at 25 deg, 35 deg, and 45 deg N for profile data to study the variation in concentrations of CO and CH4 as a function of altitude and latitude in continental air over the eastern seaboard of the United States. The experiment was repeated several months later to determine if there were seasonally dependent variations in the CO and CH4 concentrations.

Condon, E.↗
NASA NTRS1979

Infrared methane spectra between 1120 per cm and 1800 per cm - A new atlas

A new atlas of CH4 lines in the 1120-1800-per cm region has been generated, based on laboratory spectra taken with a Nicolet interferometer at 0.06-per cm resolution with 635-cm path length at pressures of 0.98 torr, 4.86 torr, and 19.97 torr. A compilation of line positions and line intensities includes 1339 CH4 lines, several hundred of which have not been previously observed.

Blatherwick, R. D.↗
NASA NTRS1979

Triton - A satellite with an atmosphere

A low-resolution infrared spectrum of Triton in the region 1.4-2.6 microns shows a broad absorption at 2.3 microns which is attributed to gaseous methane. The computed surface partial pressure of CH4, based on a random band model extrapolation of new laboratory spectra, is (1 + or - 0.5) times 10 to the -4th bars, a value consistent with the calculated vapor pressure of methane gas above methane ice at the expected temperature of Triton. There is, however, no compelling evidence for the presence of solid CH4 on the satellite's surface.

Cruikshank, D. P.↗
NASA NTRS1979

On seasonal phenomena in Saturn's atmosphere - New observations of Saturn's 3nu3 methane band

Saturn's 3nu3 CH4 band has been reobserved during April-June 1976, using the same telescope and spectrographic set-up used to study this band during the 1970 apparition. Direct comparison of the ratio spectra Saturn/moon reveals greater absorption in the manifold cores during 1976, but the increase is not as pronounced as that for the stronger CH4 bands. The rotational temperature and effective pressure of this band did not change significantly. These results are interpreted in terms of a possibly seasonal settling of the upper boundary of Saturn's atmospheric haze layer.

Trafton, L.↗
NASA NTRS1979

Organic chemistry on Titan

Features taken from various models of Titan's atmosphere are combined in a working composite model that provides environmental constraints within which different pathways for organic chemical synthesis are determined. Experimental results and theoretical modeling suggest that the organic chemistry of the satellite is dominated by two processes: photochemistry and energetic particle bombardment. Photochemical reactions of CH4 in the upper atmosphere can account for the presence of C2 hydrocarbons. Reactions initiated at various levels of the atmosphere by cosmic rays, Saturn 'wind', and solar wind particle bombardment of a CH4-N2 atmospheric mixture can account for the UV-visible absorbing stratospheric haze, the reddish appearance of the satellite, and some of the C2 hydrocarbons. In the lower atmosphere photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3 to exist. It is concluded that the surface of Titan may contain ancient or recent organic matter (or both) produced in the atmosphere.

Chang, S.↗
NASA NTRS1980

The D/H ratio in the atmosphere of Uranus - Detection of the R sub 5 /1/ line of HD

Observations of Uranus during the 1975, 1976, and 1978 apparitions reveal a weak absorption at the wavelength of the R5(1) line of HD with equivalent width 1.0 + or - 0.4 mA. The D/H ratio in Uranus' atmosphere implied by this line and other published spectra is (0.000048 + or - 0.000015), and may not be significantly different from that in the atmospheres of Jupiter and Saturn. In addition, the spectra exhibit two weak absorptions at 6044.76 + or - 0.02 and 6045.54 + or 0.02 A which were not identifiable. No trace of absorption is visible near these wavelengths or near the HD wavelength in a laboratory spectrum of 4.92 km-am CH4 which was obtained in an attempt to identify these absorption features and to verify that the HD feature does not arise from CH4.

Trafton, L.↗
NASA NTRS1980

Application of methane band-model parameters to the visible and near-infrared spectrum of Uranus

Laboratory band-model absorption coefficients of CH4 were used to calculate the Uranus spectrum from 5400 to 10,400 A. A good fit for both strong and weak bands for the Uranus spectrum over the entire wavelength interval was achieved; three atmospheric models were employed: (1) a reflecting layer model; (2) a homogeneous scattering layer model; and (3) a clear atmosphere sandwiched between two scattering layers. The spectrum for the reflecting layer model shows serious discrepancies but indicates that large amounts of CH4 are necessary to reproduce the Uranus spectrum. Both scattering models gave reasonably good fits; the homogeneous model requires a particle scattering albedo of at least 0.998 and an abundance per scattering mean free path of about 1 km-am. For the sandwich model, a continuum single scattering albedo of 0.995 was derived for the upper scattering layer, and the scattering optical depth variable wavelength was consistent with Rayleigh scattering.

Benner, D. C.↗