Engineering topics

Levine, J. S.

Publications and source records attributed to Levine, J. S..

At least 55 records · Page 3

NASA NTRS1982

Production of nitric oxide by lightning on Venus

The first measurements of the production of nitric oxide (NO) by a laboratory discharge in a simulated Venus atmosphere are presented. The average NO yield over a range of energies was found to be 3.7 + or - 0.7 x 10 to the 15th molecules/joule. Simultaneous measurements of carbon monoxide (CO) resulting from the lightning-induced dissociation of carbon dioxide (CO2) indicated a CO yield of about 4 x 10 to the 17th molecules/joule. These measurements suggest that at and below cloud level, a region where solar ultraviolet radiation cannot penetrate, the dissociation of CO2 by lightning may be a significant source of oxygen atoms. Depending on the assumed value for the total energy dissipated by lightning on Venus, the production of NO by lightning may be a significant sink of atmospheric nitrogen over the history of Venus.

Levine, J. S.↗

NASA NTRS1982

The photochemistry of the paleoatmosphere

Recent progress in the understanding of the chemistry and photochemistry of the paleoatmosphere is reviewed with emphasis on the application of photochemical models to the investigation of the evolution of the atmosphere. Photochemical calculations are presented which show that a primordial highly reducing atmosphere composed of methane and ammonia, if it formed at all, would be short-lived in the presence of solar ultraviolet radiation, giving way rapidly to a more mildly reducing atmosphere of carbon dioxide and nitrogen. Estimations of O2 produced from the photolysis of water vapor prior to the emergence of photosynthesis range from less than 10 to the -14th to 0.1 times the present atmospheric level, indicating the need for further research. A series of photochemical models of increasing complexity has been developed to study the evolution of atmospheric ozone taking into account reactions with O atoms, hydrogen oxides, nitrogen oxides, and chlorine as well as vertical transport, temperature and tropospheric chemistry so that the total content and vertical distribution of O3 may be determined for a specified level of paleoatmospheric O2.

Levine, J. S.↗

NASA NTRS1982

Ammonia and the NOx budget of the troposphere

Liu et al. (1980) suggested that NOx transported from the stratosphere, as opposed to the anthropogenic source of NOx, may be the dominant source that controls the distribution of NOx in the global troposphere. These ideas require a reinvestigation, and, in particular, an assessment of the role of the oxidation of ammonia as a source of NOx. Attention is given to the results of an ammonia measurement program, in which the vertical distribution of ammonia in the troposphere and lower stratosphere could be studied with the aid of the Infrared Heterodyne Radiometer (IHR), a solar-viewing remote sensor. A one-dimensional photochemical model of the troposphere reported by Levine et al. (1980) was employed to study the chemical and physical processes that control the loss of ammonia in the troposphere. The results of the considered investigation suggest that the oxidation of ammonia may indeed be a significant source of NOx in the troposphere.

Levine, J. S.↗

NASA NTRS1982

PAN and the NOx budget of the troposphere

The present investigation has the objective to examine the interaction of NOx with the nonmethane hydrocarbons (NMHCs) photochemistry. Attention is given to the influence of temperature, transport, and hydrocarbon radical reactions on the profiles of peroxyacylnitrates (PANs) and NO2. A lumped NMHC chemical reaction scheme was used in a one-dimensional photochemical model of the global troposphere. Model calculations were performed with various temperature profiles and the corresponding solar zenith angles to examine seasonal variations in the profiles of PAN and NOx. A study of the effects of changing temperature and solar zenith angle on the profiles of PAN and NOx showed that the amount of NO2 tied up in PAN increased as temperature decreased.

Brewer, D. A.↗

NASA NTRS1982

The chlorine budget of the troposphere

It has been hypothesized that chlorine compounds in the stratosphere could photodissociate and release atomic chlorine which catalytically destroys ozone. For an accurate assessment of the possibility of stratospheric ozone depletion, it will be necessary to know the chlorine budget of the entire atmosphere, including the troposphere and the stratosphere. Most chlorine species in the atmosphere are emitted at the surface and diffuse upward. Measurements involving chlorine are reviewed and photochemical calculations are discussed. It is found that between 0.1-1.0 ppbv of inorganic chlorine is present at the surface and about 0.02 ppbv (parts per billion by volume) at the tropopause. Most of the inorganic chlorine is believed to be in the form of HCl, and thus natural in origin. For organic chlorine the corresponding numbers are 1.9 ppbv and 1.7 ppbv, respectively. At the surface approximately 32% of the organic chlorine is natural and 68% anthropogenic.

Augustsson, T. R.↗

NASA NTRS1982

UV radiation from the young sun and oxygen and ozone levels in the prebiological palaeoatmosphere

UV measurements of young T-Tauri stars, resembling the sun at an age of a few million years, have recently been made with the International Ultraviolet Explorer. They indicate that young stars emit up to 10,000 times more UV than the present sun. The implications for the origin and evolution of O2 and O3 in the prebiological palaeoatmosphere are presented here. The results of photochemical calculations indicate that the O2 surface mixing ratio was a factor 10,000-1,000,000 times greater than the standard value of 10 to the -15. This new value reconciles the simultaneous existence of oxidized iron and reduced uranium.

Canuto, V. M.↗

NASA NTRS1982

The relevance of the IUE results on young stars for Earth's paleoatmosphere

Using the latest IUE results for seven T Tauri stars, which are believed to represent the young Sun and a detailed photochemical chemical model of the paleoatmosphere, the vertical distribution of Oxygen and Ozone in the early atmosphere was calculated. The calculations indicate that the surface Oxygen mixing ratio is as much as six orders of magnitude larger than previously estimated, but appears low enough for the formation of amino acids via the Urey-Miller type of experiments. It is believed that the quantification of the oxygen level in the Earth's paleoatmosphere presented can reconcile the demands of both biological and geological considerations.

Canuto, V. M.↗

NASA NTRS1982

The effects of isotropic multiple scattering and surface albedo on the photochemistry of the troposphere

The present study is believed to be the first investigation which combines a detailed tropospheric photochemical model with a radiative code that realistically considers the important physical processes in the cloudless troposphere which control the transfer of incoming solar radiation. It is found in most cases that the inclusion of the multiple scattering code significantly alters the photolytic reaction frequencies. This in turn alters the vertical distribution of some key tropospheric species. In the case of ozone a decrease was found, while O(1D) and OH showed increased concentrations. The increases are especially evident for the species which are highly dependent on photolysis processes that occur shortward of about 320 nm. The photolysis frequencies for ozone photolysis calculated with the Anderson-Meier model are in general in excellent agreement with recent measurements

Augustsson, T. R.↗

NASA NTRS1982

The global troposphere - Biogeochemical cycles, chemistry, and remote sensing

The chemical composition of the troposphere is controlled by various biogeochemical cycles that couple the atmosphere with the oceans, the solid earth and the biosphere, and by atmospheric photochemical/chemical reactions. These cycles and reactions are discussed and a number of key questions concerning tropospheric composition and chemistry for the carbon, nitrogen, oxygen and sulfur species are identified. Next, various remote sensing techniques and instruments capable of measuring and monitoring tropospheric species from the ground, aircraft and space to address some of these key questions are reviewed. Future thrusts in remote sensing of the troposphere are also considered.

Levine, J. S.↗

NASA NTRS1981

Photochemistry in planetary atmospheres

Widely varying paths of evolutionary history, atmospheric processes, solar fluxes, and temperatures have produced vastly different planetary atmospheres. The similarities and differences between the earth atmosphere and those of the terrestrial planets (Venus and Mars) and of the Jovian planets are discussed in detail; consideration is also given to the photochemistry of Saturn, Uranus, Pluto, Neptune, Titan, and Triton. Changes in the earth's ancient atmosphere are described, and problems of interest in the earth's present troposphere are discussed, including the down wind effect, plume interactions, aerosol nucleation and growth, acid rain, and the fate of terpenes. Temperature fluctuations in the four principal layers of the earth's atmosphere, predicted decreases in the ozone concentration as a function of time, and spectra of particles in the earth's upper atmosphere are also presented. Finally, the vertical structure of the Venus cloud system and the thermal structure of the Jovian planets are shown graphically.

Levine, J. S.↗

NASA NTRS1981

Simultaneous measurements of NO/x/, NO, and O3 production in a laboratory discharge - Atmospheric implications

Simultaneous measurements of NO(x) (NO + NO2), NO, and O3 production in a laboratory discharge show that within the uncertainties of the experiment, all of the NO(x) produced was NO, and no detectable enhancement of O3 after the discharge was observed. The laboratory experiments described gave an NO production rate of 5 + or - 2 x 10 to the 16th molecules/joule mole for a 100,000-1,000,000 joules/m spark. Assuming that the global dissipation of lightning energy is about 10 to the -8th joules/sq cm per sec (Dawson, 1980; and Hill et al., 1980), the NO production rate results in a global source of NO due to lightning of about 1.8 Mt(N)/yr, which is considerably lower than earlier estimates. This lower value for NO(x) production by lightning suggests that NO(x) emissions from anthropogenic sources, estimated to be at least 20 MT(N)/yr, may be the dominant source of NO(x) to the global troposphere. Furthermore, since most of the anthropogenic sources of NO(x) are located in the Northern Hemisphere, this new interpretation of the relative source strengths of this species favors a highly skewed asymmetric distribution of NO(x).

Levine, J. S.↗

NASA NTRS1981

Atmospheric ammonia - Measurements and modeling

Ammonia possesses a unique position in the terrestrial atmosphere in that it is the only gaseous basic constituent. Ammonia readily forms aerosols, and by virtue of its high solubility controls the pH of cloud droplets and precipitation. Over the past year a ground-based solar viewing Infrared Heterodyne Radiometer has been used at Langley Research Center to infer the vertical distribution of ammonia. Ground level in situ measurements of ammonia have also been obtained to supplement the profile data. The ammonia profiles have been analyzed and interpreted with a one-dimensional photochemical model of the troposphere to assess the sources and sinks of NH3.

Hoell, J. M., Jr.↗

NASA NTRS1981

Comets and the photochemistry of the paleoatmosphere

Ozone (O3) is a key atmospheric gas in considerations of the photochemistry/chemistry of the paleoatmosphere, chemical evolution, and the origin and evolution of life. The photochemistry/chemistry of atmospheric O3 in the paleoatmosphere is investigated using a one-dimensional photochemical model that includes the chemistry of oxygen, nitrogen, hydrogen, carbon, and chlorine gases. The role of cometary influx of H2O on the photochemistry of the paleoatmosphere is also examined. Recently, it has been suggested that the planet received a significant portion of the volatiles presently in the atmospheric/oceanic/biospheric system from cometary volatile influx. Several consequences of a cometary H2O influx on the photochemistry and structure of the paleoatmosphere are presented.

Levine, J. S.↗

NASA NTRS1980

Surface solar ultraviolet radiation for paleoatmospheric levels of oxygen and ozone

Many investigators have concluded that the level of solar ultraviolet radiation (200-300 nm) reaching the surface was a key parameter in the origin and evolution of life on earth. The level of solar ultraviolet radiation between 200 and 300 nm is controlled primarily by molecular absorption by ozone, whose presence is strongly coupled to the level of molecular oxygen. In this paper, a series of calculations is presented of the solar ultraviolet radiation reaching the surface for oxygen levels ranging from 0.0001 the present atmospheric level to the present level. The solar spectrum between 200 and 300 nm has been divided into 34 spectral intervals. For each spectral interval, the solar ultraviolet radiation reaching the earth's surface has been calculated by considering the attenuation of the incoming beam due to ozone and oxygen absorption. A one-dimensional photochemical model of the atmosphere was used for these calculations.

Levine, J. S.↗

NASA NTRS1980

Plasma double-layers produced by ponderomotive force

Non-linear rectification of the RF electric fields excited in a convectively amplifying electron beam-plasma interaction results in a dc electric field, and a corresponding ponderomotive force acting on the charged particles to produce a space-charge separation, i.e. a type of plasma double-layer. This paper analyses the effect, taking into account plasma electron temperature and electron-neutral collisions. To measure such double-layers, an electron beam probe constitutes a convenient non-perturbing diagnostic technique, but great care is required in its calibration. An analysis is presented taking into account significant non-linear effects which had been neglected in previous work. The paper concludes with some preliminary experimental results illustrating the use of the technique in a beam-plasma interaction for which a weak double-layer electric field is predicted.

Levine, J. S.↗

NASA NTRS1980

Langmuir probe measurements of double-layers in a pulsed discharge

Langmuir probe measurements have been carried out which confirm the occurrence of double-layers in an argon positive column. Pulsing the discharge current permitted probe measurements to be performed in the presence of the double-layer. Supplementary evidence, obtained from dc and pulsed discharges, indicated that the double-layers formed in the two modes of operation were similar. The double-layers observed were weak and stable; their relation to other classes of double-layers is discussed, and directions for future work are suggested.

Levine, J. S.↗

NASA NTRS1980

Ozone, ultraviolet flux and temperature of the paleoatmosphere

The development of surface and atmospheric levels of paleoatmospheric ozone is calculated by means of a detailed photochemical model and used to determine the levels of ultraviolet flux to the surface and the surface and atmospheric temperatures of the primitive earth. The model takes into account the chemistry of oxygen, nitrogen and hydrogen species and the effects of vertical transport in an atmosphere originally composed of as much N2, H2O and CO2 as the present atmosphere to which O2 is added to calculate the vertical profiles of O3 and nitrogen oxides as a function of O2 content. Calculations show that as oxygen content increases from 0.0001 to 1 times its present value, the height of the ozone peak moves from 5 to 25 km, and that maximum ozone densities are achieved for an O2 level of 0.1 times the present. Calculations of solar UV absorption by atmospheric species indicate the presence of a UV window between 200 and 220 nm that closed only when O2 reached 0.01 times its present level. Finally, calculations made using a radiative-convective model reveal that O3 levels corresponding to an O2 level of 0.1 times the present result in a globally averaged surface temperature increase of about 4.5 K for the present solar constant.

Levine, J. S.↗

NASA NTRS1980

The vertical distribution of tropospheric ammonia

A one-dimensional tropospheric photochemical model is used to simulate measured profiles of NH3 obtained with the Infrared Heterodyne Radiometer. The relative roles of homogeneous loss, heterogeneous loss, and vertical eddy transport are discussed in terms of selecting parameters which best fit the measurements. The best fit was obtained for a vertical eddy diffusion coefficient of 200,000/sq cm per sec or greater (corresponding to a characteristic vertical transport time in excess of about 35 days), and a characteristic heterogeneous loss time in excess of 10 days. The characteristic homogeneous chemical loss time was found to be about 40 days at the surface and decreased to about 180 days at 10 km, and not very sensitive to model chemical perturbations. Increased ground-level concentrations of NH3 to about 10 ppb, compared to background surface concentrations of about 1 ppb, were measured several weeks after application of ammonium nitrate fertilizer. This suggests that the volatilization of ammonium nitrate fertilizer is rapid, and an important source of NH3. Because of the characteristic times for the loss mechanisms, synoptic time-scale phenomena may play an important role in determining the tropospheric distribution of NH3 concentrations.

Levine, J. S.↗