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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Photochemistry of SO2 in Venus' upper cloud layers

The photochemical and transport processes that occur in the Venusian atmosphere in and above the upper cloud region are characterized with attention to the correlation with the Pioneer Venus spectrometer results for the cloud top SO2 distribution. The model uses upward-flowing SO2 and H2O to replace the sulfur and hydrogen lost through the lower boundary by the settling of sulfuric acid aerosols. Oxygen for the oxidation of SO2 to SO3 prior to hydration to H2SO4 is supplied by the photolysis of CO2. A model with SO2 as the major sulfur-bearing gas is consistent with the Pioneer data.

Winick, J. R.↗
NASA NTRS1980

The clouds of Venus - A synthesis report

The results presented represent a synthesis of data from those Pioneer Venus experiments directed toward studying cloud problems. These orbiter and multiprobe experiments show the cloud system to consist of three altitude regions populated by cloud particles and smaller haze particles which extend above and below as well as coexist with the cloud particles. The optical properties derived are only consistent with the largest particles, having platelike morphology. The smallest particles are shown to require changes in chemical composition to explain observed behavior. The medium-sized H2SO4 droplets of 2 micrometers diameter appear to be the least volatile and are the best understood. The role of the cloud particles in precipitation dynamical processes, lightning, and radiation are all discussed.

Knollenberg, R.↗
NASA NTRS1980

Cloud and haze properties from Pioneer Venus polarimetry

Linear polarization measurements made by the Pioneer Venus orbiter cloud photopolarimeter determined that the low and midlatitude visible clouds mainly contain small H2SO4 droplets with an extensive haze of submicron particles above the cloud group. The polarization of the bright areas poleward of the 55 deg latitude results from the haze which exhibits large spatial and temporal variations. Significant diurnal differences are observed at low latitudes, with more haze close to the morning terminator than near the noon meridian.

Kawabata, K.↗
NASA NTRS1982

Infrared absorption of sulfur bearing compounds

The sulfur bearing molecules of most interest in studies of planetary atmospheres are the simple, stable hydrides and oxides, H2S, H2SO4, SO2, and SO3, and the carbon containing species OCS and CO2. For interpreting spectroscopic observations, the properties that must be known are: transition frequencies, transition intensities, transition assignments in terms of quantum number assignments and lower state energy levels, and pressure broadening constants (including their temperature dependence).

Maki, A.↗
NASA NTRS1982

Thermochemical generation of hydrogen

The direct fluid contact heat exchange with H2SO4 at about 330 C prior to high temperature decomposition at about 830 C in the oxygen release step of several thermochemical cycles for splitting water into hydrogen and oxygen provides higher heat transfer rates, savings in energy and permits use of cast vessels rather than expensive forged alloy indirect heat exchangers. Among several candidate perfluorocarbon liquids tested, only perfluoropropylene oxide polymers having a degree of polymerization from about 10 to 60 were chemically stable, had low miscibility and vapor pressure when tested with sulfuric acid at temperatures from 300 C to 400 C.

Lawson, D. D.↗
NASA NTRS1982

Temperature dependence of the formation of sulfate aerosols in the stratosphere

Classical nucleation theory is used in calculations of the temperature dependence of the characteristics and nucleation rates of sulfate aerosols in the binary H2SO4-H2O vapor mixture, in order to assess the influence of temperature on the formation of sulfate aerosols in the stratosphere, and to explore the possibility of new particle formation through homogeneous nucleation processes at regions where temperature is as low as -75 C, rather than the often-assumed -50 or -55 C. Calculation results indicate that the number of particles formed at a lower temperature is larger by several orders of magnitude than at higher temperatures, when water and sulfuric acid vapor concentrations are kept constant, and that large quantities of ultrafine particles which cannot be detected by conventional methods may exist at low-temperature stratospheric regions.

Yue, G. K.↗
NASA NTRS1982

Photochemistry of the stratosphere of Venus - Implications for atmospheric evolution

The photochemistry of the Venus stratosphere is modeled using an updated and expanded chemical scheme along with the results of recent observations and laboratory studies. Three models, with H2 mixing ratio equal to 2 x 10 to the -5th, 5 x 10 to the -7th, and 1 x 10 to the -13th, respectively, are examined. All three models are found to satisfactorily account for the observations of CO, O2, O2(1Delta), and SO2 in the stratosphere, but only the last one may be able to account for the diurnal behavior of mesospheric CO and the UV albedo. Oxygen, derived from CO2 photolysis, is mainly consumed by CO2 recombination and oxidation of SO2 to H2SO4. The photolysis of HCl in the upper stratosphere provides a major source of odd hydrogen and free chlorine radicals, essential for the catalytic oxidation of CO. Oxidation of SO2 by O occurs in the lower stratosphere. The modeling reveals a number of interesting similarities, previously unsuspected between the chemistry of the stratosphere of Venus and that of the earth; photochemistry may have played a major role in the evolution of the atmosphere.

Yung, Y. L.↗
NASA NTRS1982

A simple method to compute the change in earth-atmosphere radiative balance due to a stratospheric aerosol layer

A computer code was developed in terms of a three-layer model for the earth-atmosphere system, using a two-stream approximation for the troposphere and stratosphere. The analysis was limited to variable atmosphere loading by solar radiation over an unperturbed section of the atmosphere. The scattering atmosphere above a Lambertian ground layer was considered in order to derive the planar albedo and the spherical albedo. Attention was given to the influence of the aerosol optical thickness in the stratosphere, the single scattering albedo and asymmetry factor, and the sublayer albedo. Calculations were performed of the zonal albedo and the planetary radiation balance, taking into account a stratospheric aerosol layer containing H2SO4 droplets and volcanic ash. The resulting ground temperature disturbance was computed using a Budyko (1969) climate model. Local decreases in the albedo in the summer were observed in high latitudes, implying a heating effect of the aerosol. An accompanying energy loss of 23-27 W/sq m was projected, which translates to surface temperature decreases of either 1.1 and 0.45 C, respectively, for background and volcanic aerosols.

Lenoble, J.↗
NASA NTRS1982

Climatic influence of background and volcanic stratosphere aerosol models

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H2SO4 particles and of volcanic ash.

Deschamps, P. Y.↗
NASA NTRS1983

Unusual behavior in the condensation nuclei concentration at 30 km

The result obtained with an improved balloon-borne condensation nuclei (CN) counter that is capable of operating to altitudes of at least 30 km are presented. Of major interest is the appearance of a quasiannual variation near 30 km which could be described by a sudden concentration increase of unusually small particles occurring in the winter or spring followed by a 1- to 3-month decay period to background levels. The magnitude of the variation has increased dramatically following the recent generally high levels of volcanic activity affecting the lower stratosphere. Several potential explanations for the event are considered, but none appear entirely satisfactory or complete at the present time. The explanation with the fewest drawbacks would attribute the production of growth of the new cn to a highly supersaturated H2SO4 vapor layer generated by any one of several proposed processes in the upper high latitude stratosphere.

Rosen, J. M.↗
NASA NTRS1983

Retrieval of stratospheric aerosol size distribution from atmospheric extinction of solar radiation at two wavelengths

A parametric study is presented of the effects of the size distribution and composition of stratospheric aerosols on the value R, the ratio of the extinction of solar radiation at wavelength 0.45 micron to the extinction at wavelength 1.0 micron. The aerosol size distributions under study comprise nine analytical expressions, including most of the stratospheric aerosol models used by investigators. The aerosol compositions considered are the supercooled sulfuric-acid droplets, with different weight percentages of H2SO4 in the aerosol. It is found that whereas R is not very sensitive to either the composition or the radii limits of the stratospheric aerosols under consideration, it is quite sensitive to the value of the variable parameter governing the mode radius of the size distribution of aerosol particles. The results of the parametric study underlie the method proposed here of retrieving the size distribution of aerosol particles in the stratosphere from the experimental results of the extinction of solar radiation at two wavelengths.

Yue, G. K.↗
NASA NTRS1983

The clouds are hazes of Venus

Pioneer Venus and Venera probe data for the clouds of Venus are considered. These clouds consist of a main cloud deck at 45-70 km altitude, with thinner hazes above and below, although the microphysical properties of the main cloud are further subdivided into upper, middle and lower cloud levels. Much of the cloud exhibits a multimodal particle size distribution, with the mode most visible from the earth being H2SO4 droplets having 2-3 micron diameters. Despite variations, the vertical structure of the clouds indicates persistent features at sites separated by years and by great distances. The clouds are more strongly affected by radiation than by latent heat release, and the small particle size and weak convective activity observed are incompatible with lightning of cloud origin.

Esposito, L. W.↗
NASA NTRS1984

Synthesis of polyamides from diamines of the fluorene series

Aromatic polyamides were prepared by polycondensation of isophthaloyl chloride and 2,7-diaminofluorene, 2,7-dimainofluorenone, or 2,5-diaminofluorenone in AcNMe2 or N-methyl-2-pyrrolidinone at 20 deg - 30 deg for 1.5-2 hr. Isophthaloyl chloride-2,5-diaminofluorenone copolymer 39609-29-51 was sol. in AcNMe2, N-methyl-2-pyrrolidinone, DMF, and hexamethylphosphoramide, whereas isophthaloyl chloride-2,7-diamino-fluorene copolymer 39609-30-3 and isophthaloyl chloride-2,7-diamino-fluorenone copolymer 39609-31-0 were not sol. in the solvents cited. The aromatic polyamides revealed thixotropic properties in 0.5% solutions in H2SO4.

Fedotova, O. Y.↗
NASA NTRS1983

Spectroscopic measurements of the 8- to 13-micrometer transmission of the upper atmosphere following the El Chichon eruptions

Infrared transmission spectra of the atmosphere above 11-km altitude were obtained at latitudes from 2 deg S to 50 deg N in December 1982. A circular variable-interference filter spectrometer mounted in a Convair 990 (the Galileo II) aircraft was used to obtain spectra of the sun through different air masses. Comparisons of spectra through different air masses provide atmospheric transmission measurements that show not only normal absorption features, such as those from CO2 and O3, but also additional absorption near 8.5 microns consistent with H2SO4 aerosols. The average fractional absorption from latitude 10 deg N to 41 deg N at 8.5 microns was 0.02/air mass, half of which was attributable to aerosols.

Witteborn, F. C.↗
NASA NTRS1983

Measurements of stratospheric SO2 after the EL Chichon eruptions

Samples of stratospheric trace gases were obtained on eight flights of NASA high-altitude aircraft from April 16 through December 13, 1982. The sampling occurred at altitudes from 15 to 22 km, latitudes from 23 to 52 deg N, and longitudes from 108 to 130 deg W. The cryogenically concentrated samples were analyzed by gas chromatography for SO2, a primary precursor of the gas-to-particle conversion process. The measured mixing ratio of SO2 varied between 8 and 132 pptv. Evidence from aerosol measurements indicates that a few of our early samples may have been collected in the fringes of the volcanic cloud from El Chichon. Samples obtained on some later flights may have been from the eruption cloud but were taken at times when most of the volcanically injected SO2 should have been converted to H2SO4.

Vedder, J. F.↗
NASA NTRS1984

Large, solid particles in the clouds of Venus - Do they exist?

The evidence for solid mode 3 particles in the clouds of Venus is reexamined. The sampling characteristics of the cloud particle size spectrometer (LCPS) are reviewed, and reasons are pointed out for believing that relatively small differences in interpreting the measurements of this instrument could produce systematic errors. It is shown that all of the Pioneer Venus and Venera measurements can be understood if it is assumed that the large particles observed by the LCPS form the tail of the mode 2, H2SO4 size distribution.

Toon, O. B.↗
NASA NTRS1984

Room-temperature luminescence from kaolin induced by organic amines

Several new, room-temperature luminescent phenomena, resulting from the interaction of kaolin and various amino compounds, have been observed. The emission of light from kaolin pastes (treated with quinoline, pyridine, hydrazine, monoethanolamine, n-butylamine, and piperidine) was shown to decay monotonically over a period of hours to days. More light was released by a given amino compound after it was dried and purified. Hydrazine, in addition to the monotonically decaying photon release, produces delayed pulses of light with peak emission wavelength of 365 nm which last between several hours and several days. These photon bursts are acutely sensitive to the initial dryness of the hydrazine, both in the number of bursts and the integrated photon output. The amount of light and the capacity of the kaolin to produce the delayed burst appeared to be strongly dependent on preliminary heating and on gamma-irradiation, analogous to the dehydration-induced light pulse previously reported from the Ames Research Center. A small, delayed burst of photons occurred when piperidine and n-butylamine were removed by evaporation into an H2SO4 reservoir.

Coyne, L. M.↗
NASA NTRS1983

Electrode kinetics of oxygen reduction - A theoretical and experimental analysis of the rotating ring-disc electrode method

In order to calculate most of the rate constants for the intermediate formation of H2O2 in the electroreduction of O2 to H2O, the theoretical treatments of the rotating ring-disc electrode method by Damjanovic et al. (1966, 1967), Bagotskii et al. (1968, 1969), and Wroblowa et al. (1976) are modified. Rotating ring-disc electrode experimental data obtained for O2 reduction in Pt in 0.55 M H2SO4 are used to illustrate the calculations of rate constants according to the above theoretical treatments. A simple reaction model as proposed by the first author is consistent with the experimental data. The results indicate that O2 (97 percent) reduces to H2O in a direct four-electron transfer reaction. The adsorption of O2 is probably the rate-determining step in the potential region more negative than 0.5 V vs. reversible hydrogen electrode.

Hsueh, K.-L.↗