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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Gas chromatographic instrumentation for the analysis of aerosols and gases in Titan's atmosphere

Instrumentation presently being developed by NASA for the collection and analysis of organic gases and aerosols in Titan's atmosphere is described together with the results of the preliminary experiments. For the aerosols, stepwise pyrolysis was shown to be a suitable method for preparing complex organic material for gas chromatography (GC), and a pyrolysis-gas chromatograph was developed and successfully used to analyze a simulated Titan aerosol. Atmospheric gases will be collected by a low-pressure gas sampling system using large-volume sample loops and analyzed by GC. The results of preliminary studies using a 20 cu cm sampling system and a very sensitive metastable ionization detector showed that hydrocarbon components at the 10 ppb level can be detected. Studies are in progress on shortening the overall analysis time by improving the pyrolysis system, the gas sampling system, and the associated gas chromatograph. Further development of the gas sampling system is planned to ensure rapid collection of samples adequate for analysis by GC over the entire range of pressures to be encountered during the probe's descent.

Scattergood, T. W.↗
NASA NTRS1987

Sources of atmospheric nitrous oxide from combustion

Emissions of nitrous oxide (N2O) have been analyzed from industrial boilers and from a large experimental combustor burning natural gas, oil, or coal. Production of N2O and production of NO(x) were observed to be correlated, with an average molar ratio of 0.58:1 (N2O-N:NO). In conventional single-stage combustors, about 14 percent of fuel nitrogen is converted to N2O and 24 percent is converted to NO(x). Conversion of fuel nitrogen to N2O was much less efficient in a two-stage experimental combustor and in wood fires. A model is presented describing emissions of N2O globally, from the beginning of the industrial revolution to the present. It is expected that concentrations of N2O should rise more than 20 percent to about 367 ppb by the year 2050, based on conservative projections of world energy consumption.

Hao, W. M.↗
NASA NTRS1988

Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon boundary layer

Tropospheric mixing ratios of methane, C2-C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 micrograms/sq m per day and 5600 micrograms/sq m per day, respectively. This isoprene emission is equivalent to 2 percent of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8-13 ppb for carbon monoxide in the planetary boundary layer.

Zimmerman, P. R.↗
NASA NTRS1988

Laboratory studies of the nitric acid trihydrate - Implications for the south polar stratosphere

Vapor pressures of HNO3 and H2O have been measured over the trihydrate crystal, formed by vapor deposit on a glass surface. In the temperature range 190 to 205 K the two phase-equilibrium trihydrate/vapor was studied by adding and removing H2O. Coexistence equilibria vapor pressures of trihydrate/solid solutions of HNO3 in ice and of mono-/trihydrate were also measured. Results show that for typical mixing ratios of H2O and HNO3 found in the lower stratosphere (3 ppm H2O, 5 ppb HNO3) the trihydrate would start to form at temperatures about 7 K higher than the ice point. The pressure of atmospheric HNO3 would rapidly decrease as the atmosphere cools without large changes in partial pressures of H2O. These laboratory results provide information on the formation of polar stratospheric clouds containing H2O and HNO3.

Hanson, David↗
NASA NTRS1988

Evidence for germane in Saturn

Observations in Saturn have prompted the development of an 0.4 + or - 0.2 ppb mole fraction for germane (GeH4) on the basis of the P- and R-branch lines' spectra. The presence of germane in Saturn implies a disequilibrium of the upper atmosphere by rapid vertical convection. It is suggested that future, more realistic radiative transfer models that include the effects of scattering within a cloud layer will probably only reduce the mole fraction presently derived for germane, by increasing the effective path length in a given atmospheric layer.

Noll, Keith S.↗
NASA NTRS1988

Southern Hemispheric nitrous oxide measurements obtained during 1987 airborne Antarctic ozone experiment

The chemical lifetime of N2O is about 150 years, which makes it an excellent dynamical tracer of air motion on the time scale of the ozone depletion event. For these reasons it was chosen to help test whether dynamical theories of ozone loss over Antarctica were plausible, particularly the theory that upwelling ozone-poor air from the troposphere was replacing ozone-rich stratospheric air. The N2O measurements were made with the Airborne Tunable Laser Absorption Spectrometer (ATLAS) aboard the NASA ER-2 aircraft. The detection technique involves measuring the diffential absorption of the IR laser radiation as it is rapidly scanned over an N2O absorption feature. For the AAOE mission, the instrument was capable of making measurements with a 1 ppb sensitivity, 1 second response time, over an altitude range of 10 to 20 kilometers. The AAOE mission consisted of a series of 12 flights from Punta Arenas (53S) into the polar vortex (approximately 72S) at which time a vertical profile from 65 to 45 km and back was performed. Comparison of the observed profiles inside the vortex with N2O profiles obtained by balloon flights during the austral summer showed that an overall subsidence had occurred during the winter of about 5 to 6 km. Also, over the course of the mission (mid-August to late September), no trend in the N2O vertical profile, either upward or downward, was discernible, eliminating the possibility that upwelling was the cause of the observed ozone decrease.

Podolske, J. R.↗
NASA NTRS1988

Iridium, shocked minerals, and trace elements across the Cretaceous/Tertiary boundary at Maud Rise, Wedell Sea, and Walvis Ridge, South Atlantic Ocean

Sediments spanning a 5 meter section across the Cretaceous-Tertiary boundary at ODP holes 689B and 690D, Maud Rise, Wedell Sea and hole 527, Walvis Ridge, are being analyzed for shock deformation, PGE's and other trace elements (including REE's). Mineral separates from each sample were studied with optical microscopy to determine the distribution and microstructural state of quartz and feldspar present in the sediments. Samples from Maud Rise were taken of the K/T transition and at about 50 cm intervals above and below it. These samples consist of carbonate-rich sediments, with the K/T transition marked by a change from white Maastrichtian oozes to a greenish ooze with higher concentrations of altered volcanic clay and vitric ash. The Walvis Ridge site is characterized by more clay-rich sediments with average carbonate content about 60 to 70 percent. Initial results from RNAA studies indicate that iridium is present in all the Maud Rise samples in concentrations equal to or greater than 0.01 ppb (whole-rock basis). Preliminary results from optical microscopy indicate the occurrence of shock mosaicism in quartz and feldspar in all of the samples studied. The pervasiveness of shock mosaicism and presence of planar features to 2 meters from the K/T boundary indicates that a single impact or volcanic explosion 66 ma may be ruled out as responsible for the K/T event. A similar conclusion may be drawn independently from the distribution of iridium and other trace elements. Regardless of the source of the shock waves and sediment contamination, multiple events are required over a ca.0.5 my timespan; currently we favor endogenous sources.

Huffman, Alan R.↗
NASA NTRS1989

Electron Spin Resonance (ESR) detection of active oxygen species and organic phases in Martian soils

The presence of active oxygen species (O(-), O2(-), O3(-)) and other strong oxidants (Fe2O3 and Fe3O4) was invoked in interpretations of the Viking biological experiments and a model was also suggested for Martian surface chemistry. The non-biological interpretations of the biological results gain futher support as no organic compounds were detected in the Viking pyrolysis-gas chromatography mass spectrometer (GCSM) experiments at concentrations as low as 10 ppb. Electron spin resonance (ESR) measures the absorption of microwaves by a paramagnetic and/or ferromagnetic center in the presence of an external field. In many instances, ESR has the advantage of detailed submicroscopic identification of the transient species and/or unstable reaction intermediates in their environments. Since the higly active oxygen species (O(-), O2(-), O3(-), and R-O-O(-)) are all paramagnetic in nature, they can be readily detected in native form by the ESR method. Active oxygen species likely to occur in the Martian surface samples were detected by ESR in UV-irradiated samples containing MgO. A miniaturized ESR spectrometer system can be developed for the Mars Rover Sample Return Mission. The instrument can perform the following in situ Martian samples analyses: detection of active oxygen species; characterization of Martian surface chemistry and photooxidation processes; and searching for organic compounds in the form of free radicals preserved in subsoils, and detection of microfossils with Martian carbonate sediments.

Tsay, Fun-Dow↗
NASA NTRS1989

Iridium enrichment in volcanic dust from blue ice fields, Antarctica, and possible relevance to the K/T boundary event

The analysis of samples of volcanic ash dust layers from the Lewis Cliff/Beardmore Glacier in Antarctica shows that some of the samples contain Ir concentrations up to 7.5 ppb. It is shown that the Ir is positively correlated with Se, As, Sb, and other volcanogenic elements. The results show that Ir may be present in some volcanic ash deposits, suggesting that the Ir in the K/T boundary clays is not necessarily of cosmic origin, but may have originated from mantle reservoirs tapped during extensive volcanic eruptions possibly triggered by impact events.

Koeberl, Christian↗
NASA NTRS1989

Trace element abundance determinations by Synchrotron X Ray Fluorescence (SXRF) on returned comet nucleus mineral grains

Trace element analyses were performed on bulk cosmic dust particles by Proton Induced X Ray Emission (PIXE) and Synchrotron X Ray Fluorescence (SXRF). When present at or near chondritic abundances the trace elements K, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Se, and Br are presently detectable by SXRF in particles of 20 micron diameter. Improvements to the SXRF analysis facility at the National Synchrotron Light Source presently underway should increase the range of detectable elements and permit the analysis of smaller samples. In addition the Advanced Photon Source will be commissioned at Argonne National Laboratory in 1995. This 7 to 8 GeV positron storage ring, specifically designed for high-energy undulator and wiggler insertion devices, will be an ideal source for an x ray microprobe with one micron spatial resolution and better than 100 ppb elemental sensitivity for most elements. Thus trace element analysis of individual micron-sized grains should be possible by the time of the comet nucleus sample return mission.

Flynn, G. J.↗
NASA NTRS1990

System development and early biological tests in NASA's biomass production chamber

The Biomass Production Chamber at Kennedy Space Center was constructed to conduct large scale plant growth studies for NASA's CELSS program. Over the past four years, physical systems and computer control software have been continually upgraded and the degree of atmospheric leakage from the chamber has decreased from about 40 to 5 percent of the total volume per day. Early tests conducted with a limited degree of closure showed that total crop (wheat) growth from the best trays was within 80 percent of reported optimal yields for similar light levels. Yields from subsequent tests under more tightly closed conditions have not been as good--up to only 65 percent of optimal yields. Yields appear to have decreased with increasing closure, yet potential problems exist in cultural techniques and further studies are warranted. With the ability to tightly seal the chamber, quantitative data were gathered on CO2 and water exchange rates. Results showed that stand photosynthesis and transpiration reached a peak near 25 days after planting, soon after full vegetative ground cover was established. In the final phase of testing when atmospheric closure was the highest, ethylene gas levels in the chamber rose from about 10 to nearly 120 ppb. Evidence suggests that the ethylene originated from the wheat plants themselves and may have caused an epinastic rolling of the leaves, but no apparent detrimental effects on whole plant function.

Wheeler, R. M.↗
NASA NTRS1989

Atmospheric methane measurement instrument using a Zeeman-split He-Ne laser

The construction of an atmospheric methane measurement instrument based on a Zeeman-split IR He-Ne laser is reported. The laser has a tranverse magnetic field over about 2/3 of its gain length and can oscillate at an (unsplit) frequency (2947.91/cm) centered on a methane absorption line, or on either of two frequencies split by + or - 0.055/cm from the center, with low CH4 absorption. The laser is tuned to dwell sequentially at each frequency, giving two differential absorption measurements in each 46-ms tuning cycle. Atmospheric measurements are made using two multiple pass absorption cells, one with fast (0.75-s) and one with slow (5-s) flow response times. Fluctuations in ambient CH4 of about 20-ppb (rms, 1-s averaging) are detected, with interference fringe effects the dominant noise source. The instrument has operated in a field experiment (NASA GTE/ABLE-3A) in Alaska.

Mcmanus, J. Barry↗
NASA NTRS1990

The abundance of AsH3 in Jupiter

Both ground-based and airborne observations of the AsH3 Q-branch at 2126/cm, in conjunction with newly-analyzed laboratory comparison spectra at AsH3, are employed in the derivation of a new estimate of Jovian As abundance. The mole fraction on AsH3 in the Jovian atmosphere is 0.22 + or - 0.11 ppb; this is merely 0.5 times the solar abundance, and a factor-of-9 less than the mole fraction found in Saturn, duplicating the pattern noted in the relative abundance of P in these two planets and furnishing a useful constraint for models of heavy element incorporation in the outer planets' gaseous envelopes.

Noll, Keith S.↗
NASA NTRS1989

Photocatalytic post-treatment in waste water reclamation systems

A photocatalytic water purification process is described which effectively oxidizes organic impurities common to reclaimed waste waters and humidity condensates to carbon dioxide at ambient temperatures. With this process, total organic carbon concentrations below 500 ppb are readily achieved. The temperature dependence of the process is well described by the Arrhenius equation and an activation energy barrier of 3.5 Kcal/mole. The posttreatment approach for waste water reclamation described here shows potential for integration with closed-loop life support systems.

Cooper, Gerald↗
NASA NTRS1990

On the determination of iridium in diverse geological samples employing HPGe-coincidence/NaI(Tl)-anticoincidence spectrometry

This paper reports the Ir content of a variety of geological samples determined by the high-purity Ge-coincidence/NaI(Tl)-anticoincidence gamma-ray spectrometry (henceforth referred to as coincidence/anticoincidence technique) and by the conventional INAA. The advantages of this technique are: (1) the Ir content of the samples is obtained (ppm to a fraction of ppb ranges) not only by the 468.1 keV peak as in the conventional INAA but also by the 784.6 keV and 920.9 keV sum peaks, which gives more confidence in the values obtained; and (2) it is well suited for the samples with high Compton background for which it is difficult to measure the Ir content by the conventional INAA technique. The practical sensitivity of this technique depends on the sample matrix. Under present experimental conditions, it varied from 0.1 ng for Mn nodules and 0.004 ng for Libyan Desert Glass. Iridium values obtained on small (about 1 microg) olivine grains demonstrate the potential application of this new technique to microsamples. The principle and methodology of this new technique as well as its advantages and disadvantages over the conventional INAA are discussed.

Murali, A. V.↗
NASA NTRS1990

Hydrogen constituents of the mesosphere inferred from positive ions - H2O, CH4, H2CO, H2O2, and HCN

The concentrations in the mesosphere of H2O, CH4, H2CO, H2O2, and HCN were inferred from data on positive ion compositions, obtained from one mid-latitude and four high-latitude rocket flights. The inferred concentrations were found to agree only partially with the ground-based microwave measurements and/or model prediction by Garcia and Solomon (1985). The CH4 concentration was found to vary between 70 and 4 ppb in daytime and 900 and 100 ppbv at night, respectively. Unexpectedly high H2CO concentrations were obtained, with H2CO/H2O ratios between 0.0006 and 0.1, and a mean HCN volume mixing ratio of 6 x 10 to the -10th was inferred.

Kopp, E.↗
NASA NTRS1990

Simultaneous, in situ measurements of OH, HO2, O3, and H2O - A test of modeled stratospheric HO(x) chemistry

Simultaneous, in situ measurements of OH, HO2, H2O, and O3 from 37-23 km are reported. The partitioning between OH and HO2 and the total HO(x) concentration are compared with expected steady-state values. The ratio of HO2 to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HO(x) production and loss rates. The measured HO(x) mixing ratio is consistent with production dominated by the reaction of O(1D) with H2O, and loss controlled by NOy below 28 km and HO(x) above 30 km. The steady-state concentration of H2O2 is inferred from the measured HO2 concentration and calculated photolysis rate. The maximum H2O2 mixing ratio (at 33 km) is predicted to be less than 0.2 ppb.

Wennberg, P. O.↗
NASA NTRS1991

A 200 MHz surface acoustic wave resonator mass microbalance

The development of a 200 MHz SAW instrument based on an SAW resonator instead of a conventional delay line is reported. The instrument is small, compact, and uses two separate 200 MHz resonataor crystals which operate in the dual difference mode. The difference frequency stability is better than 5 x 10 to the -9th (+ or - 1 Hz) which is comparable to a 10 MHz bulk crystal and at least an order of magnitude better than other commercially available SAW delay lines that operate at comparable frequencies. The mass sensitivity is about 9 x 10 to the 10th Hz sq cm/g. Response to temperature change is found to be about 20 Hz/C from -30 C to 30 C. Response to pressure is found to be linear from 760 to 415 Torr at 3 Hz/Torr. Detection limits for HCl vapors were determined to be in the low ppb range using an SAW resonator coated with triethanolamine.

Bowers, W. D.↗