Engineering topics

Augustsson, T. R.

Publications and source records attributed to Augustsson, T. R..

At least 19 records

NASA NTRS1986

The young sun, the early earth and the photochemistry of oxygen, ozone and formaldehyde in the early atmosphere

Recent work on the evolution of the solar nebula and the subsequent formation of planets is reviewed, and the stages of star formation thought to lead to a protosun and an accompanying solar nebula are considered. Photochemical results suggest that concentrations of O2, O3, and H2CO, and the ratio of CO/CO2 in the prebiological paleoatmosphere are very sensitive to atmospheric levels of H2O and CO2 and to the flux of incident solar ultraviolet. For enhanced levels of CO2 and solar UV, surface levels of O2 may have approached the parts per billion level in the prebiological paleoatmosphere. It is suggested that 10 percent or more of the enhanced H2CO production could have been rained out of the atmosphere into the early oceans where synthesis into more complex organic molecules could have taken place. CO/CO2 values of greater than unity could have been possible for enhanced levels of solar UV flux.

Canuto, V. M.↗

NASA NTRS1985

The photochemistry of biogenic gases in the early and present atmosphere

The distribution of gases in the prebiologial paleoatmosphere is investigated using photochemical models. A chart of the photochemical and chemical reactions and reaction rates for CH4, NH3, H2S, N2O, and CO atmospheric gases is given. Mixing ratios and surface mixing ratios for CH4, NH3, CO, and N2O are obtained using thermodynamic equilibrium calculations; an increase in CH4 and N2O is observed. The reactions, which explain the photochemistry of the gases studied, are presented. The sources of these gases and their concentration with regards to altitude are examined. Graphs of the vertical distribution of CH4, NH3, H2S, CO, O2, and N2O in prebiological paleoatmosphere are provided. The data reveals the presence of only N2, CO2, and N2O in the early atmosphere; with the evolution of life, sources of atmospheric gases increased and their influence on the photochemistry of the troposphere and stratosphere increased.

Levine, J. S.↗

NASA NTRS1984

Tropospheric sources of NO(x) - Lightning and biology

Laboratory tests were performed to quantify the expected NO(x) production by lightning and biological processes. Attention was focused on energy deposition by lightning and the oxygen partial pressure of soil, and one-dimensional photochemical models were defined for the tropospheric distributions of NO and HNO3 for various NO source strengths. The Lightning Facility data were compared with air samples of N2O production gathered during over 2 yr of flights through storms. Soil NO(x) productions were studied in terms of nitrification processes involving Nitrosomonas europaea and Alcaligenes faecalis bacteria, which change ammonium to nitrite and release NO and N2O as byproducts. The results indicate that atmospheric NO(x) is generated at two tropospheric levels, with lightning and soil bacteria being significant contributors.

Levine, J. S.↗

NASA NTRS1984

The oxidation of isoprene in the troposphere - Mechanism and model calculations

Calculations have been performed for 15 deg N and 45 deg N latitude continental conditions using a one-dimensional, steady state photochemical model that incorporates a chemical mechanism describing the oxidation of isoprene by OH and O3 in the troposphere. At the higher latitude, anthropogenic hydrocarbon emission effects on NO(x) vertical profiles, as well as those of HNO3, overshadow isoprene emissions effects; at the lower latitude, reduced anthropogenic emissions and increased isoprene emissions respectively yield 26 and 4 percent increases in NO(x) and HNO3 column contents. It is suggested that a significant quantity of isoprene goes to the formation of longer carbon chain oxygenated organic species.

Brewer, D. A.↗

NASA NTRS1984

Tropospheric sources of NOx: lightning and biology

Laboratory experiments to quantify the global production of NOx (NO + NO2) in the troposphere due to atmospheric lightning and biogenic activity in soil are presented. These laboratory experiments, as well as other studies, suggest that the global production of NOx by lightning probably ranges between 2 and 20 MT(N)y-1 of NO and is strongly dependent on the total energy deposited by lightning, a quantity not well-known. In our laboratory experiments, nitrifying micro-organisms is soil were found to be a significant source of both NO and nitrous oxide (N2O). The measured production ratio of NO to N2O averaged 2-3 for oxygen partial pressures of 0.5-10%. Extrapolating these laboratory measurements to the global scale, which is somewhat risky, suggests that nitrifying micro-organisms in soil may account for as much as 10 MT(N) y-1 of NO. Additional experiments with denitrifying micro-organisms gave an NO to N2O production ratio ranging from 2 to 4 for an oxygen partial pressure of 0.5% and a ratio of less than unity for oxygen partial pressures ranging from 1 to 20%. The production of NO and N2O, normalized with respect to micro-organism number indicates that the production of both NO and N2O by denitrifying micro-organisms is at least an order of magnitude less than production by nitrifying micro-organisms for the micro-organisms studied.

Atmosphere/chemistry↗

NASA NTRS1983

The young sun and the atmosphere and photochemistry of the early earth

The origin and evolution of the earth's early atmosphere depend crucially on the dissipation time of the primitive solar nebula (SN). Using different theories of turbulence, the dissipation time of an SN of 0.1 solar mass is estimated as 2.5-8.3 Myr. Because accretion times are usually much longer, it is concluded that most planetary accretion must have occurred in a gas-free environment. Using new IUE data, a wavelength-dependent UV flux is constructed for the young sun which is then used to study the photochemistry and concentrations of O, O2, O3, OH, H, HCO and formaldehyde H2CO in the earth's early prebiological atmosphere.

Canuto, V. M.↗

NASA NTRS1983

The photochemistry of anthropogenic nonmethane hydrocarbons in the troposphere

A lumped, nonmethane hydrocarbon (NMHC) chemical mechanism is presently applied to a one-dimensional photochemical model of the troposphere. The profiles of OH, HO2, NO(x), and HNO3, showed only slight changes when NMHC chemistry was added. The integrated column of peroxyacetylnitrate (PAN), when NMHC chemistry was included, comprised 17 percent of the odd nitrogen budget. Advection is noted as an important possible mechanism for the removal of PAN at midlatitudes. The inclusion of such intermediate lifetime species as aldehydes and olefins has both provided additional sources of short-lived NMHC radicals, such as the peroxyacetyl radical that is the radical precursor of PAN, and offered a more detailed description of the concentrations of short-lived species and the overall NMHC chemistry.

Brewer, D. A.↗

NASA NTRS1983

Oxygen and ozone in the early earth's atmosphere

The precise amount of O2 and O3 in the earth's prebiological paleoatmosphere has been a topic of considerable discussion in the past. Since the photolysis of H2O and CO2, the prebiological mechanisms to produce O2, depends on the ultraviolet flux from the Sun, a reliable quantification of the problem requires detailed knowledge of such flux. Using the most recent astronomical observation of young stars from the International Ultraviolet Explorer, as well as a detailed photochemical model of the paleoatmosphere, it is found that the amount of O2 in the prebiological paleoatmosphere may have been as much as a million times greater than previously estimated. Some of the implications of this new value are discussed.

Canuto, V. M.↗

NASA NTRS1982

The prebiological paleoatmosphere - Stability and composition

In the past, it was generally assumed that the early atmosphere of the earth contained appreciable quantities of methane (CH4) and ammonia (NH3). This was the type of atmosphere believed to be the most suitable environment for chemical evolution, the nonbiological formation of complex organic molecules, the precursors of living systems. Photochemical considerations suggest that a CH4-NH3 dominated early atmosphere was probably very short-lived, if it ever existed at all. Instead, an early atmosphere of carbon dioxide (CO2) and nitrogen (N2) is favored by photochemical as well as geological and geochemical considerations. Photochemical calculations also indicate that the total oxygen column density of the prebiological paleoatmosphere did not exceed 10 to the -7th of the present atmospheric level.

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 NTRS1981

Effects of multiple scattering and surface albedo on the photochemistry of the troposphere

The effect of treatment of incoming solar radiation on the photochemistry of the troposphere is discussed. A one dimensional photochemical model of the troposphere containing the species of the nitrogen, oxygen, carbon, hydrogen, and sulfur families was developed. The vertical flux is simulated by use of the parameterized eddy diffusion coefficients. The photochemical model is coupled to a radiative transfer model that calculates the radiation field due to the incoming solar radiation which initiates much of the photochemistry of the troposphere. Vertical profiles of tropospheric species were compared with the Leighton approximation, radiative transfer, matrix inversion model. The radiative transfer code includes the effects of multiple scattering due to molecules and aerosols, pure absorption, and surface albedo on the transfer of incoming solar radiation. It is indicated that significant differences exist for several key photolysis frequencies and species number density profiles between the Leighton approximation and the profiles generated with, radiative transfer, matrix inversion technique. Most species show enhanced vertical profiles when the more realistic treatment of the incoming solar radiation field is included

Augustsson, T. R.↗

NASA NTRS1981

The sulfur budget of the troposphere

A one dimensional photochemical tropospheric model was used to calculate the vertical profiles of tropospheric species. Particular attention is focused on the recent inclusion of the chemistry of the sulfur group, which consists of 13 species involving a total of 45 chemical reactions. It is found that the chemistry of the sulfur species, because it is largely anthropogenic, plays an increasingly important role in the distribution of tropospheric gases. The calculated vertical profiles were compared to available measurements and generally found to be in good agreement.

Tiwari, S. N.↗

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.↗