Influence Of Photochemical Reactions Research Articles

Influence of Photochemical Reactions on the Content and Transformation of Mineral Nitrogen in Sod-Podzol Soil

The article discusses the photochemical effects of sunlight on the soil. Under the influence of light energy the amount of mineral and easy hydrolysable nitrogen, as well as labile humus substances increased in the soil. The photochemical destruction of humus substances was accompanied by an increase in their mobility and loss of colour. The article shows that the process of mineral nitrogen formation in the soil during the photochemical destruction of humus substances has two stages. The first stage includes photochemical reactions with the formation of ammonium nitrogen. The second stage is the microbiological oxidation of ammonium nitrogen to the nitrate nitrogen.

Influence of photochemical reactions on the complexation of humic acid with europium(III)

Photochemical reactions in the Eu(III)–humic acid system are investigated by fluorescence spectroscopy. For comparison, humic acid without europium is also studied. Irradiation is performed by high energy laser beam and a low pressure mercury lamp. The impact of photodegradation on spectroscopic properties, size and decomposition of humic acid is monitored by steady state and time-resolved fluorescence spectroscopy, UV–Vis spectroscopy, gel permeation chromatography (GPC), dissolved organic carbon (DOC) analysis and ultrafiltration. The different indicators for photodegradation show different sensitivity. The decrease in DOC content with increasing irradiation dose is lower than the decrease in UV/Vis absorption. The highest impact is found for the fluorescence intensity. At 3 kJ/mg humic acid absorbed energy and in absence of europium, fluorescence diminishes by more than 90%. In the presence of Eu(III), however, fluorescent groups are partly stabilized in this range of absorbed energy. Results from GPC show changes in the chemical structure, especially generation of smaller entities. The photodegradation of the humic acid leads to a decrease of the europium–humate complexation constant. Furthermore, europium is reduced to the divalent state. The present study shows that for metal ion humic acid complexation studies by laser fluorescence spectroscopy, great care is needed to avoid significant experimental artifacts, such as photodegradation and metal ion redox reactions.

Modelling land atmosphere exchange of gaseous oxides of nitrogen in Europe

This review outlines current understanding of the exchange processes and methods used to estimate regional NOy deposition. Several methods have been used to measure dry deposition. Measurement artefacts such as non-stationarity caused by local sources, monitors responding to other gases than NO2 and the influence of photochemical reactions have made field measurement very difficult. Several measurements have shown that deposition of HNO3 is limited only by the rate of its aerodynamic transport to the surface leading to deposition velocities as large as 10 cm s-1 to forest. For NO the situation is more complex. Early laboratory studies using high concentrations showed stomatal uptake. However detailed field studies carried out more recently at ambient concentrations show that most ecosystems emit NO. -from Authors

A thermal description of the melting of c- and a-silicon under pulsed excimer lasers

Abstract The thermal melting calculations for crystalline and amorphous silicon under pulsed UV excimer lasers include the most recent values for the thermal and optical parameters of Si in the UV range. The melting threshold, melt duration and depth of fusion are calculated in different irradiation conditions and compared to the various experimental values already published or measured in our laboratory. The influence of photochemical reactions which can take place in the gas phase at UV wavelength, on the purely thermal process will be also briefly discussed.

Influence of photochemical reactions on the optical properties of aquatic humic substances gained from fall leaves

Fulvic acids were isolated from leaves leachate which had seen no light, and were characterized by spectroscopic methods (UV-VIS; fluorescence; FT-IR; laser flash). The results are compared with those for irradiated (254 nm) samples and with those for humic substances isolated from a brownwater lake. There is a significant bleaching effect at long term irradiation and a loss of dissolved organic carbon, especially in the presence of oxygen. Humic substances which have not been exposed to light seem to be more photoreactive than irradiated ones. Excitation experiments provide evidence for the existence of transients with a lifetime of 10 to 100 ps. The results are helpful for the understanding of the genesis of humic substances.

The Photochemistry of the Upper Atmosphere of Jupiter

Abstract Photochemical processes which must occur in the upper atmosphere of Jupiter are discussed and the significance of recent data pertinent to such reactions is analyzed. These data include (a) the ultraviolet solar radiation flux, (b) velocity constants and activation energies for many of the reactions, (c) absorption coefficients for some of the atmospheric constituents, and (d) semi-quantitative values for concentrations of major atmospheric constituents. A rough calculation of the influence of photochemical reactions on the atmospheric composition is described. The results suggest that molecular hydrogen undergoes a slow photolysis to a considerable depth in the atmosphere thus maintaining the high concentrations of methane and ammonia.