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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Dispersal of gases generated near a lunar outpost

The dispersal of gases evolved by prospective lunar base operations is presently modeled analytically using continuous (mining and habitat-venting) and impulsive (primarily rocket exhaust) injections of gases. In the case of impulsive injection, the neutral atmosphere and associated ionosphere both decay on time-scales of about 20 min; in that of continuous injection, the atmosphere near the base grows and achieves a steady state after about 20 min. Both direct and diffusive transport mechanisms are considered, and it is concluded that for the injection rates and assumptions presently employed the artificial lunar atmospheres produced are not significantly detrimental to astronomical observations and high-vacuum materials processing operations.

Burns, Jack O.↗
NASA NTRS1991

Submillimeter heterodyne remote sensing of upper atmospheric gases

Technology now becoming available for submillimeter heterodyne remote sensing of upper atmospheric gases is discussed. The general features of microwave limb sounding are reviewed, and the UARS Microwave Limb Sounder, a NASA mission dedicated to the comprehensive and integrated study of earth's upper atmosphere, is briefly described. The EOS Microwave Limb Sounder is briefly examined, showing its expected measurement capability for various gases.

Waters, Joe W.↗
NASA NTRS1990

The strange gases of Jupiter and Saturn

The various gases found in the atmospheres of Jupiter and Saturn are discussed. A history of scientific investigation of these planets is outlined and results of these discoveries are considered. The molecular species found in these two planets are classified into several groups. The first group consists of H2, He, CH4, NH3, and H2O while the second group contains gases formed as the chemical byproducts of solar radiation, including simple hydrocarbons such as C2H2 and C2H6 and charged particles such as H3(+). The last group contains compounds which are chemically unstable in parts of Jupiter's atmosphere that have been probed and include Ge and As; two elements usually found in minerals on earth. An investigation of origin of these elements which are currently part of the upper reaches of the atmosphere of Jupiter and Saturn has led to discoveries about much deeper and hotter parts of atmospheres that can never be observed directly. A number of hypotheses are presented to account for the presence of various unexpected compounds, such as carbon monoxide.

Noll, Keith S.↗
NASA NTRS1991

Composition of solar wind noble gases released by surface oxidation of a metal separate from the Weston meteorite

The paper reports on a set of experiments intended to test the feasibility of determining elemental and isotopic ratios of the noble gases and nitrogen in the solar wind in metal separates from gas-rich ordinary chondrites. Helium, neon, and argon show clear evidence of a solar wind signature, while no solar component could be identified for xenon and nitrogen. Helium, neon, and argon elemental isotopic ratios appear to depend on depth within the metal grains. The ratios derived indicate that the Weston meteorite did not acquire its solar wind gases from a recent exposure to solar wind, but more probably at a time in the past similar to or even earlier than the exposure time of Apollo 17 breccias. The Ar-36/Ar-38 ratio, in tandem with other recent determinations of this value, indicates that the solar and terrestrial values can no longer be assumed to be equivalent.

Becker, R. H.↗
NASA NTRS1991

Theoretical computation of trace gases retrieval random error from measurements of high spectral resolution infrared sounder

The purpose of this paper is to demonstrate the trace gas profiling capabilities of future passive high spectral resolution (1 cm(exp -1) or better) infrared (600 to 2700 cm(exp -1)) satellite tropospheric sounders. These sounders, such as the grating spectrometer, Atmospheric InfRared Sounders (AIRS) (Chahine et al., 1990) and the interferometer, GOES High Resolution Interferometer Sounder (GHIS), (Smith et al., 1991) can provide these unique infrared spectra which enable us to conduct this analysis. In this calculation only the total random retrieval error component is presented. The systematic error components contributed by the forward and inverse model error are not considered (subject of further studies). The total random errors, which are composed of null space error (vertical resolution component error) and measurement error (instrument noise component error), are computed by assuming one wavenumber spectral resolution with wavenumber span from 1100 cm(exp -1) to 2300 cm(exp -1) (the band 600 cm(exp -1) to 1100 cm(exp -1) is not used since there is no major absorption of our three gases here) and measurement noise of 0.25 degree at reference temperature of 260 degree K. Temperature, water vapor, ozone and mixing ratio profiles of nitrous oxide, carbon monoxide and methane are taken from 1976 US Standard Atmosphere conditions (a FASCODE model). Covariance matrices of the gases are 'subjectively' generated by assuming 50 percent standard deviation of gaussian perturbation with respect to their US Standard model profiles. Minimum information and maximum likelihood retrieval solutions are used.

Huang, Hung-Lung↗
NASA NTRS1991

Laminar flames in premixed gases

Numerical simulation of laminar flames in premixed gases is addressed. Various efforts to solve the laminar flame problem are briefly described, and basic equations to be modeled in a comprehensive description of laminar flames are discussed along with the physical and chemical processes represented by these equations and the numerical requirements to model them. Two flame methods are discussed in some detail: a numerical model for studying transient phenomena and its 2D counterpart method. The various input parameters needed for the models are addressed, and the use of the models is illustrated in several studies of laminar flames in premixed gases. Flammability limits and multidimensional flame propagation are also examined.

Kailasanath, K.↗
NASA NTRS1989

Photochemistry of biogenic gases

The relationship between the biosphere and the atmosphere is examined, emphasizing the composition and photochemistry and chemistry of the troposphere and stratosphere. The reactions of oxygen, ozone, and hydroxyl are reviewed and the fate of the biogenic gases ammonia, methane, reduced sulfur species, reduced halogen species, carbon monoxide, nitric oxide, nitrous oxide, nitrogen, and carbon dioxide are described. A list is given of the concentration and sources of the various gases.

Levine, Joel S.↗
NASA NTRS1992

Possible cometary origin of heavy noble gases in the atmospheres of Venus, earth, and Mars

Due consideration of the probable history of the Martian atmosphere, as well as noble-gas data from the Mars-derived SNC meteorites and from laboratory tests on the trapping of noble gases in ice, are the bases of the presently hypothesized domination of noble gases in the atmospheres of all terrestrial planets by a mixture of internal components and a contribution from comets. If verified, this hypothesis would underscore the significance of impacts for these planets' volatile inventories. The sizes of the hypothesized comets are of the order of 120 km for Venus and only 80 km for that which struck the earth.

Owen, Tobias↗
NASA NTRS1992

Soluble species in the Arctic summer troposphere - Acidic gases, aerosols, and precipitation

The large-scale spatial distribution from 0.15-to 6 km altitude in the North American Arctic troposphere of several soluble acidic gases and major aerosol species during the summertime is reported. The distribution is found to be compositionally consistent on a large spatial scale. The summertime troposphere is an acidic environment, with HCOOH and CH3COOH the principal acidic gases while acidic sulfate aerosols dominate the particulate phase. There appears to be a surface source of NH3 over the pack ice which may originate from decay of dead marine organisms on the ice surface, evolution from surface ocean waters in open ice leads, or release from rotting sea ice. At low altitude over the pack ice this NH34 appears to partially neutralize aerosol acidity. Over sub-Arctic tundra in southeastern Alaska, inputs of marine biogenic sulfur from the Bering Sea appear to be an important source of boundary layer aerosol SO4(2-). The rainwater acidity over the tundra is typical of remote regions.

Talbot, R. W.↗
NASA NTRS1993

Rotational level-dependent collisional broadening and line shift of the A2Sigma(+)-X2Pi (1,0) band of OH in hydrogen-air combustion gases

Measurements of the collisional broadening and line shift of the (1,0) band of the A2Sigma(+)-X2Pi system of OH are reported in atmospheric pressure hydrogen-air combustion gases. The measurements were made using a single-mode, narrow linewidth, frequency-doubled ring dye laser operating near 283 nm. The OH was generated in the combustion gases of a flat flame H2-air burner. Collisional broadening parameters for equilibrium mixtures of H2, O2, H2O, and N2 were obtained spanning a range of fuel/air equivalence ratios from 0.6 to 1.6 and temperatures from 1500 to 2050 K. Measurements were obtained spanning rotational quantum numbers from 4.5 to 16.5. The collision induced frequency shift was determined to be 0.1 that of the collisional broadening.

Kessler, W. J.↗
NASA NTRS1992

Trapping of noble gases in proton-irradiated silicate smokes

We have measured Ne, Ar, Kr, and Xe in Si2O3 'smokes' that were condensed on Al substrates, vapor-deposited with various mixtures of CH4, NH3, H2O3 and noble gases at 10 K and subsequently irradiated with 1 MeV protons to simulate conditions during grain mantle formation in interstellar clouds. Neither Ne nor Ar is retained by the samples upon warming to room temperature, but Xe is very efficiently trapped and retained. Kr is somewhat less effectively retained, typically depleted by factors of about 10-20 relative to Xe. Isotopic fractionation favoring the heavy isotopes of Xe and Kr of about 5-10-percent/amu is observed. Correlations between the specific chemistry of the vapor deposition and heavy noble gas retention are most likely the result of competition by the various species for irradiation-produced trapping sites. The concentration of Xe retained by some of these smokes exceeds that observed in phase Q of meteorites and, like phase Q, they do not seem to be carriers of the light noble gases.

Nichols, R. H., Jr.↗
NASA NTRS1993

The relative roles of sulfate aerosols and greenhouse gases in climate forcing

Calculations of the effects of both natural and anthropogenic tropospheric sulfate aerosols indicate that the aerosol climate forcing is sufficiently large in a number of regions of the Northern Hemisphere to reduce significantly the positive forcing from increased greenhouse gases. Summer sulfate aerosol forcing in the Northern Hemisphere completely offsets the greenhouse forcing over the eastern United States and central Europe. Anthropogenic sulfate aerosols contribute a globally averaged annual forcing of -0.3 watt per square meter as compared with +2.1 watts per square meter for greenhouse gases. Sources of the difference in magnitude with the previous estimate of Charlson et al. (1992) are discussed.

Kiehl, J. T.↗
NASA NTRS1992

Origin of noble gases in the terrestrial planets

Current models of the origin of noble gases in the terrestrial planets are reviewed. Primary solar system volatile sources and processes are examined along with the current data base on noble gases and its applications to evolutionary processing. Models of atmospheric evolution by hydrodynamic escape are addressed.

Pepin, Robert O.↗
NASA NTRS1991

Biomass burning and the production of greenhouse gases

The present discussion of related aspects of biomass burning describes a technique for estimating the instantaneous emission of trace gases generated by such fires on the basis of satellite imagery, and notes that burning results in significantly enhanced biogenic emissions of N2O, NO, and CH4. Biomass burning therefore has both immediate and long-term impacts on the trace-gas content of the atmosphere. The effects of Kuwait's oil fires, which encompass both combustion gases and particulates, are compared with those of the more general problem.

Levine, Joel S.↗
NASA NTRS1935

Relation of Hydrogen and Methane to Carbon Monoxide in Exhaust Gases from Internal-Combustion Engines

The relation of hydrogen and methane to carbon monoxide in the exhaust gases from internal-combustion engines operating on standard-grade aviation gasoline, fighting-grade aviation gasoline, hydrogenated safety fuel, laboratory diesel fuel, and auto diesel fuel was determined by analysis of the exhaust gases. Two liquid-cooled single-cylinder spark-ignition, one 9-cylinder radial air-cooled spark-ignition, and two liquid-cooled single-cylinder compression-ignition engines were used.

Gerrish, Harold C↗
NASA NTRS1951

The Flow of Gases in Narrow Channels

Measurements were made of the flow of gases through various narrow channels a few microns wide at average pressures from 0.00003 to 40 cm. Hg. The flow rate, defined as the product of pressure and volume rate of flow at unit pressure difference, first decreased linearly with decrease in mean pressure in the channel, in agreement with laminar-flow theory, reached a minimum when the mean path length was approximately equal to the channel width, and then increased to a constant value. The product of flow rate and square root of molecular number was approximately the same function of mean path length for all gases for a given channel.

FLOW, LAMINAR↗
NASA NTRS1992

Emissions of sulfur gases from wetlands

Data on the emissions of sulfur gases from marine and freshwater wetlands are summarized with respect to wetland vegetation type and possible formation mechanisms. The current data base is largest for salt marshes inhabited by Spartina alterniflora. Both dimethyl sulfide (DMS) and hydrogen sulfide (H2S) dominate emissions from salt marshes, with lesser quantities of methyl mercaptan (MeSH), carbonyl sulfide (COS), carbon disulfide (CS2) and dimethyl disulfide (DMDS) being emitted. High emission rates of DMS are associated with vegetation that produces the DMS precursor dimethylsulfonionpropionate (DMSP). Although large quantities of H2S are produced in marshes, only a small percentage escapes to the atmosphere. High latitude marshes emit less sulfur gases than temperate ones, but DMS still dominates. Mangrove-inhabited wetlands also emit less sulfur than temperate S. alterniflora marshes. Few data are available on sulfur gas emissions from freshwater wetlands. In most instances, sulfur emissions from temperate freshwater sites are low. However, some temperate and subtropical freshwater sites are similar in magnitude to those from marine wetlands which do not contain vegetation that produces DMSP. Emissions are low in Alaskan tundra but may be considerably higher in some bogs and fens.

Hines, Mark E.↗