Photochemical effects in the production of cometary radicals and ions.
Photochemical production of cometary molecular radicals and ions, comparing observed densities with calculations based on photodissociation and photoionization
Donn, B.↗
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Photophysical and photochemical properties of sterically hindered aryldiazonium salts
Sterically hindered aryldiazonium salts absorption spectra and quantum yield data interpretation, considering photochemical properties
Bushnell, P.↗
Photochemical rearrangement of NN- dimethylphenylethynylamine into alpha- phenylisobutyronitrile
Photochemical molecular rearrangement of NN- dimethylphenylethynylamine into alpha- phenylisobutyronitrile by irradiation at 254 nm
Boyer, J. H.↗
Problem of photochemical equilibrium of ozone in planetary atmospheres: Ozone distribution in the lower atmosphere of Mars
The inherent errors of applying terrestrial atmospheric ozone distribution studies to the atmosphere of other planets are discussed. Limitations associated with some of the earlier treatments of photochemical equilibrium distributions of ozone in planetary atmospheres are described. A technique having more universal application is presented. Ozone concentration profiles for the Martian atmosphere based on the results of the Mariner 4 radio occultation experiment and the more recent results with Mariner 6 and Mariner 7 have been calculated using this approach.
Grams, G. W.↗
Photochemical synthesis of simple organic free radicals on simulated planetary surfaces - An ESR study
Electron spin resonance (ESR) spectroscopy provided evidence for formation of hydroxyl radicals during ultraviolet photolysis (254 nm) at -170 C of H2O adsorbed on silica gel or of silica gel alone. The carboxyl radical was observed when CO or CO2 or a mixture of CO and CO2 adsorbed on silica gel at -170 C was irradiated. The ESR signals of these radicals slowly disappeared when the irradiated samples were warmed to room temperature. However, reirradiation of CO or CO2, or the mixture CO and CO2 on silica gel at room temperature then produced a new species, the carbon dioxide anion radical, which slowly decayed and was identical with that produced by direct photolysis of formic acid adsorbed on silica gel. The primary photochemical process may involve formation of hydrogen and hydroxyl radicals. Subsequent reactions of these radicals with adsorbed CO or CO2 or both yield carboxyl radicals, CO2H, the precursors of formic acid. These results confirm the formation of formic acid under simulated Martian conditions and provide a mechanistic basis for gauging the potential importance of gas-solid photochemistry for chemical evolution on other extraterrestrial bodies, on the primitive earth, and on dust grains in the interstellar medium.
Tseng, S.-S.↗
Formation of fatty acids in photochemical conversions of saturated hydrocarbons
Abiogenic synthesis of fatty acids was studied in photochemical conversions of saturated hydrocarbons. It was shown that, in a hydrocarbon water CaCO3 suspension, the action of 254 nm UV rays caused the formation of fatty acids with a maximum number of carbon atoms in the chain not exceeding that in the initial hydrocarbon. Synthesis of acetic, propionic, butyric, valeric, caproic, enanthic and caprylic (in the case of octane) acids occurs in heptane water CaCO3 and octane water CaCO3 systems.
Telegina, T. A.↗
The distribution of ammonia and its photochemical products on Jupiter
Altitude profiles of ammonia and its photochemical products are generated in the light of measurements of the Jovian temperature structure, eddy transport coefficient, improved chemical scheme, and rate constants. Realistic limits are placed on the concentration of hydrazine which may participate in the recycling of ammonia on Jupiter. The maximum hydrazine-ice production rate is calculated to be about 1.3 mg/sq m per Jovian day. The distribution of nitrogen gas is presented with and without supersaturation of hydrazine. The nitrogen mixing ratio near the ammonia cloud top is estimated to be in the range between 10 to the -9th and 10 to the -11th power. An appreciable latitudinal variation in the ammonia concentration is expected.
Atreya, S. K.↗
Photochemical-radiative damping and instability in the stratosphere
At the stratopause, when opacity effects are included, the photochemical acceleration of the thermal relaxation rate is substantially reduced and large vertical scale temperature disturbances relax at approximately the Newtonian cooling rate. Large vertical scale ozone density and temperature perturbations may grow in amplitude due to opacity changes in the O3 dissociation and heating rates.
Strobel, D. F.↗
The photochemical role of tropospheric nitrogen oxides
The role of nitrogen oxides in the tropospheric photochemical system is re-evaluated in the light of recent measurements of the rate constants for two key reactions. A model for nitrogen oxides is discussed which yields surface NO(x) (NO+NO2) levels approaching 1 ppb in NO(x) source regions but less than 0.1 ppb outside source regions. Applying the new rate coefficients implies increased radical concentrations and a more intense O3 and CO photochemistry. Even for densities of 0.1 ppb or less, NO(x) still leads to significant local O3 production and conversion of HO2 to OH. Unrealistic O3 profiles are obtained with the new rate coefficients for surface NO(x) densities of about 1 ppb, while reasonable agreement with observation is obtained with lower NO(x) densities. Feedback processes between CO, NO(x), OH, and CH4 are also discussed.
Chameides, W. L.↗
A coupled radiative-convective-photochemical model of the stratosphere
A one-dimensional atmospheric model is described. The neutral photochemical processes of the troposphere and stratosphere are presented by a reaction set of 87 kinetic processes and 28 photolytic reactions, with vertical transport being taken into account by an eddy diffusion parameter. The vertical temperature profiles are coupled with the chemical calculations by means of a radiative-convective code. The model has the capability of including effects of multiple scattering and diurnal variations in species concentrations. The numerical solution methodology is described in detail, and current input data are given along with results obtained in a sample calculation.
Boughner, R. E.↗
Chemical kinetic and photochemical data for use in stratospheric modelling
An evaluated set of rate constants and photochemical cross sections were compiled for use in modelling stratospheric processes. The data are primarily relevant to the ozone layer, and its possible perturbation by anthropogenic activities. The evaluation is current to, approximately, January, 1979.
Demore, W. B.↗
Abundance of organic compounds photochemically produced in the atmospheres of the Outer Planets
Organic photochemical syntheses in the Jovian atmosphere was simulated by irradiating, at 147 nm, gaseous mixtures of methane and ammonia with varying amounts of hydrogen. Some results relevant to the photochemistry of the Jupiter atmosphere at several tens of kilometers above the clouds were obtained: (1) a favorable effect of the pressure of high amounts of H2 on the yield of hydrocarbon synthesis when NH3 is mixed with CH4; (2) a very low yield of synthesis of unsaturated hydrocarbons in such conditions; and (3) the possibility of formation of detectable amounts of HCN and CH3CN.
Raulin, F.↗
Thermal structure and relaxation rates of the perturbed atmosphere - A study with a photochemical radiative convective model
A radiative-photochemical model is developed to evaluate the temperature distribution in the earth's atmosphere between the ground and 70 km. The model takes into account the interaction between photochemistry and temperature. Results are reported for a number of experiments performed with this model to assess the climatic effects of varying the ozone distribution and the ozone overburden. An evaluation of the relaxation rates of both ozone and temperature is also reported. In particular, the importance of the ozone distribution with respect to the greenhouse effect is further investigated.
Alimandi, G.↗
Introductory study of the chemical behavior of jet emissions in photochemical smog
Jet aircraft emissions data from the literature were used as initial conditions for a series of computer simulations of photochemical smog formation in static air. The chemical kinetics mechanism used in these simulations was an updated version which contains certain parameters designed to account for hydrocarbon reactivity. These parameters were varied to simulate the reaction rate constants and average carbon numbers associated with the jet emissions. The roles of surface effects, variable light sources, NO/NO2 ratio, continuous emissions, and untested mechanistic parameters were also assessed. The results of these calculations indicate that the present jet emissions are capable of producing oxidant by themselves. The hydrocarbon/nitrous oxides ratio of present jet aircraft emissions is much higher than that of automobiles. These two ratios appear to bracket the hydrocarbon/nitrous oxides ratio that maximizes ozone production. Hence an enhanced effect is seen in the simulation when jet exhaust emissions are mixed with automobile emissions.
Whitten, G. Z.↗
Photochemical production of formaldehyde in earth's primitive atmosphere
Formaldehyde could have been produced by photochemical reactions in the earth's primitive atmosphere, at a time when it consisted mainly of molecular nitrogen, water vapor, carbon dioxide, and trace amounts of molecular hydrogen and carbon monoxide. Removal of formaldehyde from the atmosphere by precipitation can provide a source of organic carbon to the oceans at the rate of 100 billion moles per year. Subsequent reactions of formaldehyde in primeval aquatic environments would have implications for the abiotic synthesis of complex organic molecules and the origin of life.
Pinto, J. P.↗
Chemical kinetic and photochemical data for use in stratospheric modeling evaluation number 4: NASA panel for data evaluation
Evaluated sets of rate constants and photochemical cross sections compiled by the Panel are presented. The primary application of the data is in the modelling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.
Source record↗
Evaluated kinetic and photochemical data for atmospheric chemistry
This paper contains a critical evaluation of the kinetics and photochemistry of gas phase chemical reactions of neutral species involved in middle atmosphere chemistry (10-55 km altitude). Data sheets have been prepared for 148 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each reaction a preferred value of the rate coefficient at 298 K is given together with a temperature dependency where possible. The selection of the preferred value is discussed, and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an appendix listing the available data on enthalpies of formation of the reactant and product species.
Baulch, D. L.↗
Photochemical processes induced by a major warming of the upper atmosphere - Variations in mesospheric trace constituents
The temperature rise and enhanced winds during an upper atmospheric warming cause substantial changes in the high level ozone profile of the sunlit winter hemisphere. Calculations based on a photochemical model, using temperatures measured at Fort Churchill during a major warming, predict a factor of 2 variation in the ozone number density near 60 km over a time period of approximately 3 weeks. This temporal variability at a fixed location results from the planetary wave structure of the temperature field and reflects a similar longitudinal behavior at a given time. The ozone number density at fixed altitude is a maximum when the temperature is greatest at and below this level. This is due primarily to thermal expansion of the atmosphere which results in a large increase in pressure at constant altitude. However, chemical activity during a warming decreases the mesospheric ozone mixing ratio at fixed pressure. The ozone mixing ratio at constant pressure during the peak of the event studied is near 75% of its unperturbed value. The predicted variability of ozone in longitude and time demonstrates the need for hemispheric scale information on trace gas abundances, temperature, and winds in order to delineate adequately the response of upper atmospheric composition to a major perturbation.
Frederick, J. E.↗