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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Injection of dust into the Martian atmosphere - Evidence from the Viking Gas Exchange experiment

The hypothesis that predawn midlatitude storms are triggered by a soil humidification process is examined. A freeze/thaw model of the process is evaluated in the Viking Gas Exchange experiments conducted on Mars. The humidification-driven desorption and desiccation state of Martian soil samples are analyzed. The periodic humidification of equatorial regolith soil is studied in terms of pore space pressure during desorption events and soil diffusivity; the thermal properties of the regolith surface layer are modeled using the program of Clifford (1984). Consideration is given to the diurnal and seasonal cycles of the humidification process, the permanent, low-albedo features in the midlatitudes, and the production of H2SO4 and HCl aerosols.

Huguenin, R. L.↗
NASA NTRS1986

Space opportunities for tropospheric chemistry research

The use of the Space Shuttle to measure tropospheric trace species is examined. Factors which affect the measurement of tropospheric trace species are discussed. The Academy of Sciences 1985 report categorized the trace species into levels: first-level gases include water vapor, O3, CO, and CH4, and the second-level gases are N2O, NO2, NH3, SO2, chlorofluoromethanes, and HCl. The effects of first-level gases on the earth's climate, the photochemistry/chemistry of the troposphere, and the photochemical/chemical production and destruction of the hydroxyl radical are studied; the distribution and magnitude of the hydroxyl radical in the troposphere are analyzed in terms of water vapor, O3, CO, and CH4.

Levine, Joel S.↗
NASA NTRS1986

Meteoric material and the behavior of upper stratospheric polar zone

Ozone mixing ratios as a function of pressure level and time are presented based on data obtained with the Nimbus-7 SBUV instrument between 1979 and 1984, and implications of this data for the explanations of the spring Antarctic ozone depletion are considered. It is suggested that meteoric atoms react with the atmosphere to bond to OH, and subsequently react with HCl to form salts, resulting in the accumulation of chlorine during polar winter. The sudden release of this chlorine from photodissociation of these salts during spring could account for the loss of ozone in the upper atmosphere.

Aikin, A. C.↗
NASA NTRS1987

Rare earth patterns in shergottite phosphates and residues

Leaching experiments with 1M HCl on ALHA 77005 powder show that rare earth elements (REE) are concentrated in accessory phosphate phases (whitlockite, apatite) that govern the REE patterns of bulk shergottites. The REE patterns of whitlockite are typically light REE-depleted with a negative Eu anomaly and show a hump at the heavy REE side, while the REE pattern of apatite (in Shergotty) is light REE-enriched. Parent magmas are calculated from the modal compositions of residues of ALHA 77005, Shergotty, and EETA 79001. The parent magmas lack a Eu anomaly, indicating that plagioclase was a late-stage crystallizing phase and that it probably crystallized before the phosphates. The parent magmas of ALHA 77005 and Shergotty have similar REE patterns, with a subchondritic Nd/Sm ratio. However, the Sm/Nd isotopoics require a light REE-depleted source for ALHA 77005 (if the crystallization age is less than 600 Myr) and a light REE-enriched source for Shergotty. Distant Nd and Sr isotopic signatures may suggest different source regions for shergottites.

Laul, J. C.↗
NASA NTRS1987

The use of atmospheric measurements to constrain model predictions of ozone change from chlorine perturbations

Atmospheric photochemistry models have been used to predict the sensitivity of the ozone layer to various perturbations. These same models also predict concentrations of chemical species in the present day atmosphere which can be compared to observations. Model results for both present day values and sensitivity to perturbation depend upon input data for reaction rates, photodissociation rates, and boundary conditions. A method of combining the results of a Monte Carlo uncertainty analysis with the existing set of present atmospheric species measurements is developed. The method is used to examine the range of values for the sensitivity of ozone to chlorine perturbations that is possible within the currently accepted ranges for input data. It is found that model runs which predict ozone column losses much greater than 10 percent as a result of present fluorocarbon fluxes produce concentrations and column amounts in the present atmosphere which are inconsistent with the measurements for ClO, HCl, NO, NO2, and HNO3.

Douglass, Anne R.↗
NASA NTRS1987

Infrared observations of circumstellar molecules

A current listing of IR observations of circumstellar molecules is presented. These observations were performed using Fabry-Perot, Fourier transform, and laser heterodyne spectroscopy. The most abundant species were CO, SiO, and HCN, while trace species included NH3, CH4, SiH4, and CS. Among the undetected species were H2, HCl, and CH2.

Betz, Albert↗
NASA NTRS1987

Heavy carbon in individual oxide grains from the Murchison meteorite

The carbon isotopic composition of individual oxide grains from Murchison HF-HCl acid residue CFOc has been measured in the ion microprobe. Many grains contain carbon with large C-13 excesses ranging to 7000 per mil. In most cases the carbon is present as micron-sized subgrains. The association of silicon with the anomalous carbon points towards SiC as carrier. If this tentative identification is correct, then the SIC grains most likely originated in the circumstellar atmospheres of red giants. Oxide grains in which the O-18/O-16 ratio has also been measured show variable O-16 excesses which are not correlated with the C-13 excesses. This indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated.

Zinner, Ernst↗
NASA NTRS1987

Glass properties in the yttria-alumina-silica system

The glass formation region in the yttria-alumina-silica system was investigated. Properties of glasses containing 25 to 55 wt pct yttria were measured and the effect of the composition was determined. The density, refractive index, thermal-expansion coefficient, and microhardness increased with increasing yttria content. The dissolution rate in 1N HCl increased with increasing yttria content and temperature. These glasses were also found to have high electrical resistivity.

Hyatt, M. J.↗
NASA NTRS1987

Reaction of chlorine nitrate with hydrogen chloride and water at Antarctic stratospheric temperatures

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO2) with H2O and HCl on surfacers that simulate polar stratospheric clouds are studied at temperatures relevant to the Antarctic stratosphere. The gaseous products of the resulting reactions, HOCl, Cl2O, and Cl2, could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the additional formation of condensed-phase HNO3 could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.

Tolbert, Margaret A.↗
NASA NTRS1988

Simultaneous measurement of minor stratospheric constituents with emission far-infrared spectroscopy

The vertical mixing ratio profiles of H2O, HDO, O3, heavy ozone, HF, HCl, HCN, and OH in the stratosphere are retrieved from high-resolution far-infrared emission spectra. These spectra were obtained with a balloon-borne Fourier transform spectrometer in the spring of 1979 at 32 deg N. The nonlinear least squares fit method is used in the analysis. The results are obtained relative to the O2 mixing ratio, whose emission features can be found in the same spectra. The retrieval of OH together with other species should be particularly significant for the study of upper stratospheric photochemistry, although the errors are relatively large: 28 percent for OH and 16-19 percent for other species.

Carli, Bruno↗
NASA NTRS1988

Infrared measurements of column abundances of several trace gases in the Antarctic atmosphere

Atmospheric emission measurements were made in 1978 from an LC 130 aircraft from Point Mugu, CA, to McMurdo Station, Antarctica, and from McMurdo over the Antarctic continent on several different flights. These included a number of flights over the South Pole. In December 1980, infrared solar spectra were obtained from the ground at South Pole Station. Infrared solar spectra were also obtained from South Pole during late November and early December of 1986. These latter measurements were extended to cover additional spectral regions to obtain column densities of a number of additional constituents. The results obtained from these measurement series are reviewed and, where measurements were made during both periods, compared. Spectral absorption or emission features due to HNO3, NO, NO2, HCl, (H-16)2O, (H-18)2O, HDO, CH4, and N2O were used to obtain data on the total column abundances for these compounds.

Murcray, F. J.↗
NASA NTRS1988

Isotopic anomalies of Ne, Xe, and C in meteorites. I - Separation of carriers by density and chemical resistance

The carriers of presolar noble gases were studied by isotopically analyzing 19 separates from the Murray and Murchison C2 chondrites for Ne, Xe, C, and N. It is found that the carriers of Ne-E(H) and Xe-S are resistant to HCl, HF, boiling HClO4, and CrO3-H2SO4, and thus must be either diamond or some resistant carbide or oxide. The carrier of Ne-E(L) may be some form of amorphous carbon with delta C13 of about +340 percent. A new carbon component, C theta, found as 0.2-2-micron inclusions in Murchison spinel, is amorphous and contains little or no noble gas. A new heavy nitrogen component is found which has an abundance of about 1 ppm in the bulk meteorite, combusts at 450-500 C, and may be associated wtih isotopically normal carbon or with C-alpha.

Ming, Tang↗
NASA NTRS1988

Formation of polar stratospheric clouds simulated in a two dimensional model of the atmosphere

A microphysics code has been implemented in a two dimensional model of the atmosphere to study formation of polar stratospheric clouds containing HCl or HNO3. The model range is from pole to pole in latitude and from the ground to about 20 km in altitude. Resolution in latitude is 10 deg and about 0.8 km in altitude. This is an Eulerian model with prescribed eddy diffusion coefficients and the circulation obtained from observations. The chemistry of the model follows the family approach for NO(x), Cl(x) and HO(x) while the ozone is fixed and changed seasonally. The aerosol code is based on an assigned population of condensation, coagulation and sedimentation. Aerosol growth is simulated in nine different size bins ranging between 0.01u and 2.56u. The model has been built to study aerosol layers formation in the upper troposphere and lower stratosphere and has been validated for sulfate aerosol resulting from a rather complex sulfur chemistry.

Visconti, Guido↗
NASA NTRS1988

Laboratory studies of sticking coefficients and heterogeneous reactions important in the stratosphere

The discovery of ozone depletion during spring in the Antarctic stratosphere has received wide spread attention. Both meteorological and chemical mechanisms have been used in attempts to explain this observation. The chemical theory focused on the chlorofluoromethanes released into the atmosphere. However, gas-phase, homogeneous reactions alone in the model can not adequately explain such a depletion. Heterogeneous reactions on ice surfaces could be important in the Antarctic stratosphere. These reactions are thought to convert ClONO2 and N2O5 into HNO3 in the solid phase while Cl2, HOCl, and ClNO2 are released into the stratosphere as gas-phase products. The photolysis of Cl2, HOCl, and ClNO2, then produces active chlorine which subsequently removes ozone through several catalytic cycles, including the Cl2O2 mechanism. The polar stratospheric clouds are thought to consist of mixtures of water ice, nitric acid, and sulfuric acid. Condensation of HCl onto the PSC's could provide active surfaces for heterogeneous reactions.

Leu, Ming-Taun↗
NASA NTRS1988

Photochemical modeling of the Antarctic stratosphere: Observational constraints from the airborne Antarctic ozone experiment and implications for ozone behavior

The rapid decrease in O3 column densities observed during Antarctic spring has been attributed to several chemical mechanisms involving nitrogen, bromine, or chlorine species, to dynamical mechanisms, or to a combination of the above. Chlorine-related theories, in particular, predict greatly elevated concentrations of ClO and OClO and suppressed abundances of NO2 below 22 km. The heterogeneous reactions and phase transitions proposed by these theories could also impact the concentrations of HCl, ClNO3 and HNO3 in this region. Observations of the above species have been carried out from the ground by the National Ozone Expedition (NOZE-I, 1986, and NOZE-II, 1987), and from aircrafts by the Airborne Antarctic Ozone Experiment (AAOE) during the austral spring of 1987. Observations of aerosol concentrations, size distribution and backscattering ratio from AAOE, and of aerosol extinction coefficients from the SAM-II satellite can also be used to deduce the altitude and temporal behavior of surfaces which catalyze heterogeneous mechanisms. All these observations provide important constraints on the photochemical processes suggested for the spring Antarctic stratosphere. Results are presented for the concentrations and time development of key trace gases in the Antarctic stratosphere, utilizing the AER photochemical model. This model includes complete gas-phase photochemistry, as well as heterogeneous reactions. Heterogeneous chemistry is parameterized in terms of surface concentrations of aerosols, collision frequencies between gas molecules and aerosol surfaces, concentrations of HCl/H2O in the frozen particles, and probability of reaction per collision (gamma). Values of gamma are taken from the latest laboratory measurements. The heterogeneous chemistry and phase transitions are assumed to occur between 12 and 22 km. The behavior of trace species at higher altitudes is calculated by the AER 2-D model without heterogeneous chemistry. Calculations are performed for solar illumination conditions typical of 60, 70, and 80 S, from July 15 to October 31.

Rodriguez, Jose M.↗
NASA NTRS1988

Chemistry of chlorinated species in the Antarctic stratosphere

The chemistry of Cl sub 2 O sub 2, the chlorine monoxide dimer, has been further investigated in order to better asses its potential role in catalytic ozone destruction cycles. The dimer has been generated in a flow system, in the 200 to 250 K temperature range, by using ozone and chlorine atoms as ClO precursors. The Cl-atoms are produced by a microwave discharge of either Cl sub 2, or of F sub 2 with subsequent addition of HCl. With this later scheme the dimer can be generated in the absence of Cl sub 2. The Fourier transform infrared spectra of the products clearly indicates the presence of two isomers, in agreement with earlier results (J. Phys. Shen., 91, 433, 1987). None of the observed IR bands can be attributed to a ClO-OClO adduct, since they all appear in the absence of any detectable amount of OCl. It is likely that the particles in the polar stratospheric clouds will have a relatively dilute nitric acid outer layer, even if the core is the nitric acid monohydrate, since the particles are in equilibrium with the ambient water vapor, which is present at levels of a few parts per million.

Molina, Mario J.↗
NASA NTRS1988

Modelling the Antarctic lower stratosphere

Results form modeling studies of the Antarctic lower stratosphere which have attempted to simulate the large springtime ozone losses and corresponding changes in other trace constituents are given. These studies were carried out in a photochemical box model, a one-dimensional model without transport and in a two-dimensional photochemical-dynamical-radiation model. The photochemical studies have investigated inter alia the sensitivity of ozone to inclusion in the model of heterogeneous chemistry, and to the inclusion of the ClO dimer. When both of these are incorporated in the model, ozone depletions resembling whose found in Halley Bay in 1987 (J.C. Farman, Nature, 329, 1987) can be reproduced. The temporal variations (both diurnal and during the August to October period) of a number of important tracers including HCl, ClONO2, OClO and BrO are discussed. The two-dimensional study concentrated on the difficulty of establishing in the model the dynamical preconditioning of the lower polar stratosphere - low temperatures, low N2O, etc., high ClOx. Calculations are presented to show: (1) the depletion of ozone during the springtime season, (2) the effect of large ozone losses on lower latitudes, and (3) the longer term (multi-year) variations of ozone in Antarctica, assuming realistic increases in the atmospheric halogen burden.

Chipperfield, M. P.↗
NASA NTRS1988

Modelling the Antarctic ozone hole

Researchers performed model calculations of the ozone depletions taking place in the Antarctic lower stratosphere. Making the assumption that odd nitrogen is frozen out on stratospheric haze particles, an analysis is given of how much homogeneous reactions can contribute to ozone loss during September-October. Comparisons with observations indicate the potential importance of reactions with HCl in the polar stratospheric cloud particles.

Crutzen, P. J.↗