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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Balloon-borne remote sensing of stratospheric constituents

Data on species of interest in the photochemistry of the ozone layer obtained from balloon flights are presented. The flights made use of remote-sensing instruments that took measurements in the wavelength region from the ultraviolet to millimeter wavelengths. Most of the data were obtained with instruments whose readings were in the midinfrared wavelengths. Descriptions are given of the two techniques generally used in this type of research, namely solar absorption and atmospheric emission. The promise that these techniques hold for providing data on the photochemistry of the ozone layer is discussed.

Murcray, D. G.↗
NASA NTRS1984

Numerical experiments with a general circulation model concerning the distribution of ozone in the stratosphere

The distribution of ozone below 60 km altitude has been simulated in two experiments employing a nine-layer quasi-geostrophic spectral model and linear parameterization of ozone photochemistry, the first of which included thermal and orographic forcing of the planetary scale waves, while the second omitted it. The first experiment exhibited a high latitude winter ozone buildup which was due to a Brewer-Dodson circulation forced by large amplitude (planetary scale) waves in the winter lower stratosphere. Photochemistry was also found to be important down to lower altitudes (20 km) in the summer stratosphere than had previously been supposed.

Kurzeja, R. J.↗
NASA NTRS1985

Strat-trop exchange

Exchange between the stratosphere and troposphere is important to the chemical composition of both regions. The export of ozone from the stratosphere provides the troposphere with a means of initiating photochemistry. The precursor molecules originating from the planetary surface provide the stratosphere with its chemical feedstock from which the ozone-controlling HO(x), NO(x), and Cl(x) photochemistries are driven. The tropopause is defined both statistically and in a local, synoptic sense by the value P(sub theta) = .000016 K sq m/kg/s, taken from an objective analysis of 8 years of zonal, temporal mean cross sections of potential temperature, wind and potential vorticity.

Tuck, A. F.↗
NASA NTRS1986

Future directions for H sub x O sub y detection, executive summary

New methods for the measurement of OH radicals were assessed as were currently available and possible future methods for the other H sub x O sub y species, HO2 and H2O2. The workshop participants were invited from different groups: modelers of atmospheric photochemistry, experimentalists measuring H sub x O y species with laser and nonlaser methods, and chemists and physicists familiar with such experiments but not involved in atmospheric monitoring. There were three major conclusions from the workshop concerning the OH radical. First, it was felt that local measurements made by laser techniques would be ready within 2 or 3 years to furnish reliable measurements at the level of 1,000,000 cu. cm. Second, measurements at this level of sensitivity and with attainable levels of precision could indeed be used to make useful and interesting tests of the fast photochemistry of the troposphere. It is important, however, that the measurements be carefully designed, with respect to spatial and temporal averaging, if there is to be a meaningful comparison between results from two experimental methods or a measurement and a model. Third, nonlocal measurements using released reactants and tracers would also be very useful. These could be made on a regional or global basis, although they still require experimental design including choice of compounds.

Source record↗
NASA NTRS1987

The 2.5-diacyl-1,4-dimethylbenzenes: Examples of bisphotoenol equivalents

The photochemistry of 2,5-dibenzoyl(DBX)-and 2,5-diacetyl-1,4-dimethylbenzene (DAX) has been investigated. Both compounds readily undergo photoenolization similar to 0-alkylphenyl ketones. However, unlike 0-alkylphenyl ketones DAX and DBX are each capable of undergoing two tandem photoenolizations. Photoenols derived from o-alkylphenyl ketones have been successfully trapped with Diels-Alder dienophiles to provide a convenient synthesis of substituted tetralins. Similarly, Diels-Alder trapping of DBX photoenils afforded substituted tetra- and octahydro anthracenes. Further mainpulation of these photadducts provided the corresponding anthracenes in good yield. The photochemistry of DAX and DBX will be discussed, in particular their use in the synthesis of substituted anthracenes.

Meador, Michael A.↗
NASA NTRS1987

Transport and photochemical modeling. Studies of atmospheric species

A program of research studies related to the photochemistry, radiative transfer, and dynamics of the stratosphere is described. Investigations were conducted in two broad areas: (1) studies of the stratospheric processes and their response to external perturbations, and (2) analysis of satellite measurements in conjunction with theoretical models. Contemporary one dimensional photochemical, radiative-convective model was used to assess the impact of perturbations such as solar flux variability, increases in atmospheric carbon dioxide, chlorofluoromethanes and other greenhouse gases. Data from satellite experiments such as LIMS and SBUV, were used along with theoretical models to develop a climatology of trace species in the stratosphere. The consistency of contemporary ozone photochemistry was examined in the light of LIMS data. Research work also includes analysis of stratospheric nitrogen dioxide distributions from different satellite experiments, investigation of the wintertime latitudinal gradients in NO2, estimation of the stratospheric odd nitrogen level and its variability, and studies related to the changes in ozone in the Antarctic, and mid latitude Southern Hemisphere.

Natarajan, M.↗
NASA NTRS1987

Net ozone photochemical production over the eastern and central North Pacific as inferred from GTE/CITE 1 observations during fall 1983

The role of photochemistry in the budget of tropospheric ozone is studied. Measurements of O3, NO, CO, H2O vapor, and temperature obtained during the fall of 1983 during the GTE/CITE project over the eastern and central North Pacific Ocean are analyzed. The effect of altitude on the measurements is discussed. The analysis reveals a correlation between ozone and NO levels; both increase in concentration and variability with altitude. It is observed that an additional source of secondary importance associated wih CO-rich air parcels exists. A photochemical model is utilized to calculate the net rate of ozone production by photochemical reactions. A net photochemical source of ozone in the free troposphere and a net sink in the boundary layer are detected. The relation between the ozone source in the free troposphere and NO is examined. It is estimated that photochemistry provides a net ozone source to the free troposphere overlying the eastern and central North Pacific Ocean of about 5 x 10 to the 10th molecules/sq cm sec and a net sink of ozone to the boundary layer overlying this region of about 3 x 10 to the 10th molecules/sq cm sec.

Chameides, W. L.↗
NASA NTRS1988

Ground-based column abundance measurements of atmospheric hydroxyl

The preliminary results of ground-based OH column abundance measurements from Truk, Federated States of Micronesia, are contained. These are the first OH column measurements from the tropics, and constitute a signficcant contribution to the OH data base. Comparisons of tropical OH behavior with the extensive mid-latitude observations serve as a critical test of the current understanding of the HO (sub x) photochemistry and its relationship to the other major chemical families. The quasi-biennial oscillation (QBO) in tropical stratospheric winds exerts a major influence on the Hadley cell vertical transport. Related QBOs in total O3 and in stratospheric H2O were identified, but QBO effects on other stratospheric species are still unknown. The solar tide in the tropics produces a diurnal surface pressure variation of 2 to 3 mb; its effect on OH photochemistry in the stratosphere may be significant.

Burnett, Clyde R.↗
NASA NTRS1988

The role of molecular hydrogen and methane oxidation in the water vapour budget of the stratosphere

The detailed photochemistry of methane oxidation has been studied in a coupled chemical/dynamical model of the middle atmosphere. The photochemistry of formaldehyde plays an important role in determining the production of water vapor from methane oxidation. At high latitudes, the production and transport of molecular hydrogen is particularly important in determining the water vapor distribution. It is shown that the ratio of the methane vertical gradient to the water vapor vertical gradient at any particular latitude should not be expected to be precisely 2, due both to photochemical and dynamical effects. Modeled H2O profiles are compared with measurements from the Limb Infrared Monitor of the Stratosphere (LIMS) experiment at various latitudes. Molecular hydrogen is shown to be responsible for the formation of a secondary maximum displayed by the model water vapor profiles in high latitude summer, a feature also found in the LIMS data.

Le Texier, H.↗
NASA NTRS1988

Global impact of the Antarctic ozone hole: Simulations with a 3-D chemical transport model

A study of the Antarctic ozone hole was made with a 3-D chemical transport model using linearized photochemistry for ozone based on observed distribution. The tracer model uses the winds and convection from the GISS general circulation model (8 deg x 10 deg x 23 layers). A 3-year control run of the ozone distribution is compared with the observed climatology. In two experiments, a hypothetical Antarctic ozone hole is induced on October 1 and on November 1; the tracer model is integrated for 1 year with the standard linearized chemistry. The initial depletion, 90 percent of the O sub 3 poleward of 70 S between 25 and 180 mbar, amounts to about 5 percent of the total O sub 3 in the Southerm Hemisphere. As the vortex breaks down and the hole is dispersed, significant depletions to column ozone, of order 10 D.U., occur as far north as 36 S during Austral summer. One year later, about 25 percent of the original depletion remains, mostly below 100 mbar and poleward of 30 S. Details of the calculations are shown, along with a budget analysis showing the fraction of the hole filled in by photochemistry versus that transported into the troposhere.

Prather, Michael J.↗
NASA NTRS1988

Experimental simulations of oxidizing conditions and organic decomposition on the surface of Mars

One important scientific objective of a Mars Rover Sample Return mission would be to look for traces of living and extinct life on Mars. An instrument to search for organic carbon may be the simplest instrument that could screen samples which are interesting from a biological point of view. An experimental program is described which would help to understand the nature of the oxidizing soil on Mars and the mechanism responsible for organic degradation on the Martian surface. This is approached by lab simulations of the actual conditions that occur on Mars, particularly the oxidant production by atmospheric photochemistry, and the combined effects of UV light and oxidants in decomposing organic compounds. The results will be used to formulate models of the photochemistry of the atmospheric, the atmosphere-soil interaction, and the diffusion of reactive compounds into the soils. This information will provide insights and constraints on the design of a sampling strategy to search for organic compounds on Mars.

Stoker, C. R.↗
NASA NTRS1989

An overview of MAP/GLOBUS NO(x)

GLOBUS NO(x) is a combined observation of nitrogen compounds by more than 20 experiments, from satellites, remote and in situ instruments on board balloons and ground observatories, within a short time period. Held in September 1985 above Southern France, the field campaign has been a technical success. Most of the observations were achieved as anticipated. NO, NO2 and relevant species and physical parameters involved in their photochemistry, were measured between 5 and 40 km at several periods of the day. A first step of data interpretation which consists of instrumental intercomparisons, is now achieved. Several systematic biases between data of various origins which have appeared in the past, are now understood and reduced. A second step which deals with atmospheric photochemistry issues like diurnal cycles and budget, is now on its way. It will be the object of a close exchange between experimenters involved in the campaign and modelers.

Pommereau, J. P.↗
NASA NTRS1991

The formation of peroxonitrites and oxygen on Mars

When Martian regolith samples are moistened with water, a strong oxidant and oxygen gas are released. The many possible oxidants which have been suggested as present, including superoxide (O2(-)) hydrogen peroxide (H2O2(-)), and manganese (IV) oxide (MnO2), as well as peroxonitrite (ONOO(-)), can be distinguished by their ability to account for the numerous observations of the Viking Labelled Release (LR) and Gas Exchange (GEX) experiments. The magnitudes, kinetics, and heat labilities of the LR experiments and the magnitudes and heat labilities of the GEX experiments have been quantitatively replicated with peroxonitrites. Further, it is to be expected from information about the photochemistry of nitrogen in the atmosphere, the calculated fluxes of the NO(x) to the surface, the known reactions of NO(x) with carbonates to produce nitrates and photolysis studies of nitrates, that peroxonitrites are present on Mars. However, considerable uncertainty has existed about the form in which oxygen is stored in photolyzed nitrate crystals. Models have ranged from micropores of O2 to chemically bound oxygen as peroxonitrite (O2NOO(-)), as well as peroxonitrite. Studies of the solution chemistry and solid state photochemistry were completed, which show that much of the oxygen evolved on wetting comes from thermal breakdown of peroxonitrite after it is dissolved. A chemical model is developed for the photochemical processes occurring during UV irradiation of solid nitrates which resolves the several contradictory models discussed in the literature in recent years.

Plumb, Robert C.↗
NASA NTRS1992

Tropospheric ozone and aerosol observations - The Alaskan Arctic

This paper discusses in situ measurements of O3, aerosol number density, and aerosol size obtained during NASA Arctic Boundary Layer Expedition aircraft flights over the Alaskan Arctic region. The major source of summer O3 for the troposphere in the intrusion of stratospheric air and subsequent transport to lower altitudes. Photochemistry of mixed layer emissions and O3 transported from high northern latitude urban/industrialized areas do not appear to play major roles as sources of O3 for the Alaska region. O3 gradients reflect the loss at the surface and supply from the stratosphere. Free tropospheric O3 averaged 74 ppbv compared to 32 ppbv for the mixed layer. O3 loss mechanisms are a combination of the destruction via photochemistry, chemical reaction with surface emissions, and direct loss through deposition to the surface. The boreal forest in the most efficient of the O3 sinks and has the largest increase in aerosol number density relative to the free troposphere.

Gregory, Gerald L.↗
NASA NTRS1992

Direct detection of C4H2 photochemical products - Possible routes to complex hydrocarbons in planetary atmospheres

The photochemistry of diacetylene (C4H2), the largest hydrocarbon to be unambiguously identified in planetary atmospheres, is of considerable importance to understanding the mechanisms by which complex molecules are formed in the solar system. In this work, the primary products of C4H2's ultraviolet photochemistry were determined in a two-laser pump-probe scheme in which the products of C4H2 photoexcitation are detected by vacuum ultraviolet photoionization in a time-of-flight mass spectrometer. Three larger hydrocarbon primary products were observed with good yield in the C4H2 + C4H2 reaction: C6H2, C8H2, and C8H3. Neither C6H2 or C8H3 is anticipated by current photochemical models of the atmospheres of Titan, Uranus, Neptune, Pluto, and Triton. The free hydrogen atoms that are released during the formation of the C8H3 and C8H2 products also may partially offset the role of C4H2 in catalyzing the recombination of free hydrogen atoms in the planetary atmospheres.

Bandy, Ralph E.↗
NASA NTRS1993

Global normal-mode Rossby waves observed in stratospheric ozone data

Westward-propagating Rossby normal-mode planetary waves are documented in stratospheric ozone data using Solar Backscatter Ultraviolet (SBUV) satellite measurements. These modes are evidenced by enhanced spectral power and near-global coherence for westward-traveling zonal wave 1 oscillations with periods of 5-10 days. The ozone waves have maxima in high latitudes of the middle stratosphere (due to transport) and over midlatitudes in the upper stratosphere (due to photochemistry). These modes are nearly continuous throughout the eight years of SBUV observations, with maximum global coherence during the equinoxes. The upper-stratospheric waves are symmetric (in phase) between hemispheres, even for modes previously identified as antisymmetric in geopotential height. This behavior is due to differing wave vertical structure in each hemisphere; the planetary temperature waves are nearly in phase in the upper stratosphere, even though the height waves are out of phase. The observed ozone waves are furthermore compared to calculations based on linear wave transport and photochemistry, incorporating derived wind and temperature fields. Good agreement is found, showing that normal modes provide an idealized context to study the linear wave behavior of trace constituents in the real atmosphere.

Randel, William J.↗
NASA NTRS1994

Quantitative understanding of the cycles of oxidized and reduced sulfur on Venus

The evolution of the Venus atmosphere is determined by the supply of gases from the interior of the planet and outer space, and by the loss of particles to space over time. In particular, questions pertaining to the initial inventory of water and the current and past rates of outgassing can be addressed by studying the loss rates of H, D, He3 and He4. The photochemistry of the H2SO4 clouds may also have played an important role in regulating the amount of water above the cloud tops, and hence limit the rate of escape of hydrogen from the planet. Thus the problems of evolution and chemistry are intimately related. In our proposal the principal tasks we undertook to advance our understanding of the origin and evolution of water on Venus included: (1) escape of light atoms from Venus and (2) develop a photochemical model of sulfate formation. In the last two years we have made progress on Task 1 regarding how light atoms can escape from the exosphere of Venus with the development of a Monte Carlo program and in Task 2 have developed a thorough update on the SO2 photochemistry that had been previously carried out.

Yung, Yuk L.↗
NASA NTRS1994

In situ measurements of the NO2/NO ratio for testing atmospheric photochemical models

Simultaneous in situ measurements of NO2, NO, O3, ClO, pressure and temperature have been made for the first time, presenting a unique opportunity to test our current understanding of the photochemistry of the lower stratospere. Data were collected from several flights of the ER-2 aircraft at mid-latitudes in May 1993 during NASA's Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE). The daytime ratio of NO2/NO remains fairly constant at 19 km with a typical value of 0.68 and standard deviation of +/- 17. The ratio observations are compared with simple steady-state calculations based on laboratory-measured reaction rates and modeled NO2 photolysis rates. At each measurement point the daytime NO2/NO with its measurements uncertainty overlap the results of steady-state caculations and associated uncertainty. Possible sources of error are examined in both model and measurements. It is shown that more accurate laboratory determinations of the NO + 03 reaction rate and of the NO2 cross-sections in the 200-220 K temperature range characteristic of the lower stratosphere would allow for a more robust test of our knowledge of NO(X) phtochemistry by reducing significant sources if uncertainties in the interpretation of statospheric measurements.

Jaegle, L.↗