Solar UV radiation

Ozone. 03, mw 48.00, triatomic oxygen, the most reactive form of oxygen a bluish, expl gas or blue liq. It is found in the atm in varying proportions (about 0.05 ppm at sea level), since it is produced continuously in the outer layers of the atm by the action of solar UV radiation on the oxygen of the air. In the laboratory ozone is prepd by passing... 

Another major feature of the vertical thermal structure of the atmosphere is due to the presence of ozone, O3, in the stratosphere. This layer is caused by photochemical reactions involving oxygen. The absorption of solar UV radiation by O3 causes the temperature in the stratosphere and mesosphere to be much higher than expected from an extension of the... 

Cancer occurs when the growth and function of cells are out of control in relation to normal tissue. The combination of genetic alterations and environmental toxins is the most frequent contributor to the process of carcinogenesis. In the development of skin cancer, the risk factors are categorized as environmental (solar UV radiation), genetic (family history), immunosuppression, and previous history of melanoma.10... 

There are new ideas and experiments on the rTCA cycle. A group from Harvard University studied some reaction steps in the rTCA cycle which were kept going by mineral photochemistry. The authors assumed that solar UV radiation can excite electrons in minerals, and that this energy is sufficient to initiate the corresponding reaction steps. In this photocatalytic process, semiconductor particles were suspended in water in the presence of a zinc sulphide colloid (sphalerite) the experiments were carried out in a 500 mL reaction vessel at 288 K. Irradiation involved a UV immersion lamp (200-410 nm) in the photoreactor. Five reactions out of a total of 11 in the rTCA cycle were chosen to check the hypothesis ... 

Pourzand, C. and Tyrrell, R. M., Apoptosis, the role of oxidative stress and the example of solar UV radiation, Photochem. Photobiol. 70, 380-390, 1999. 

Photocatalytic degradation of environmental pollutants by solar energy is a very attractive technology for the remediation of contaminated water [253,323], In some variants of this process, solar UV radiation is absorbed by semiconductor catalyst particles suspended in water. TiOz photocatalytic particles are the most widely used for these applications. 

CC12FCC1F2. These compounds are non-toxic and non-flammable, and their thermodynamic properties are ideally suited for the compression/ expansion cycle in cooling and heat pump appliances. However, CFCs are chemically very inert, so when they are vented into the atmosphere, they do not react with atmospheric constituents. They diffuse unscathed first into the troposphere, then penetrate slowly into the stratosphere. There, the solar UV radiation photodissociates these compounds, liberating free chlorine atoms (the C-Cl bond is weaker than the C-F bond). The chlorine atoms react with atmospheric O3 to form chlorine oxide, which in turn reacts with atmospheric atomic oxygen regenerating chlorine atoms ... 

Although the focus of this chapter is tropospheric HO measurements, it is worthwhile to mention techniques that have proven useful in the laboratory or in other regions of the atmosphere. As a small molecule in the gas phase, HO has a much-studied and well-understood discrete absorption spectrum in the near UV (29), shown in Figure 1, that lends itself to a variety of absorption and fluorescence techniques. The total atmospheric HO column density has been measured (30-32) from absorption of solar UV radiation, observed with a high-resolution scanning Fabry-Perot spectrometer. Long-path measurements of stratospheric HO from its thermal emission spectra in the far infrared have been reported (33-35). Long absorption paths in the atmospheric boundary layer have been used for HO detection from its UV absorption (36-42). 

Blumthaler, M., Ambach, W., and Huber, M. (1993) Altitude effect of solar UV radiation dependent on albedo, turbidity, and solar elevation, Meteorol. Z, N.F. 2,116-120. 

The STAR model is applied to build up the geographic patterns of solar UV radiation in Italy. The daily UV (290-325 nm) dose is calculated in a number of Italian sites taking into account the climatology of each site as well as the topographic features. The results are interpreted in terms of atmospheric and meteorological factors affecting UV radiation. 

M. Nicolet, Solar UV radiation and its absorption in the mesosphere and stratosphere, Pure Appl. Geophys., 118, 3 (1980). 

Tranvik, L. J., and S. Bertilsson. 1999. Contrasting effects of solar UV radiation on dissolved organic sources for bacterial growth. Ecology Letters 4 458—463. 

The presence of the ozone layer ensures that solar UV radiation (in the wavelength range 2-300 nm) which is harmful to living things is prevented [by reaction (2a)] from reaching the Earth s surface. Since ozone is known from laboratory studies to be destroyed by some atmospheric pollutants and the photofragments thereof 17), pollution of the atmosphere (particularly by freons) has recently been the... 

Stachowicz, J.J. and Lindquist, N., Chemical defense among hydroids on pelagic Sargassum predator deterrence and absorption of solar UV radiation by secondary metabolites, Mar. Ecol. Prog. Ser., 155, 115, 1997. 

Drollet, J. H., Teai, T., Faucon, M., and Martin, P. M. V., Field study of compensatory changes in UV-absorbing compounds in the mucus of the solitary coral Fungia repanda (Scleractinia Fungiidae) in relation to solar UV radiation, sea-water temperature, and other coincident physico-chemical parameters, Mar. Freshwater Res., 48, 329, 1997. 

In the precambrian (or on present day Mars), the absence, of an ozone layer allowed solar UV radiation with energies as high as 40,000 cm"1 (0.25 microns). Photoreduction transitions via the Fe(3d) to Fe(4s) transition may have been very significant. The photochemical oxidation of Fe2+, and the precipitation of FeOOH, may be the origin of the extensive precambrian banded iron formations (38-40). Moreover, the photooxidation of Fe2 may have reduced C02 to organic molecules (37.41) ... 

Similar to ozonation processes, since the discovery of the germicidal effects of solar UV radiation by Downes and Blount in 1877 [13], UV radiation was first used for disinfection. The development of reaction mechanisms in photochemistry led to the discovery of the advantages of UV radiation as an oxidation technology. At room temperature, most molecules... 

During weathering, phenolic antioxidants are photooxidized into hydroperoxycy-clohexadienones, such as 59 (Pospisil, 1993 Pospisil, 1980). The presence of peroxidic moieties in 57 and 59 renders them thermolabile at temperatures exceeding 100 °C and photolysable under solar UV radiation. Both processes account for homolysis of the peroxidic moieties. As a result, the oxidative degradation of the polymeric matrix is accelerated by formed free-radical fragments (tests were performed with atactic polypropylene and acrylonitrile-butadiene-styrene terpolymer (ABS) (PospiSil, 1981 PospiSil, 1980). Low-molecular-weight products of homolysis, such as 60 to 63 are formed in low amounts. 

The other amino acid residue present in proteins that is susceptible to oxidation is the indole moiety of tryptophan (Fig. 11). The reducing potential of tryptophan is considerably less than that of cysteine and methionine, so oxidation of tryptophanyl residues usually does not occur until all exposed thiol residues are oxidized. Also, the spontaneous oxidation of tryptophanyl residues in proteins is much less probable than that of cysteinyl and methionyl residues. Tryptophan residues are the only chromophoric moieties in proteins which can be photooxi-dized to tryptophanyl radicals by solar UV radiation, even by wavelengths as long as 305 nm (B12). Tryptophanyl residues readily react with all reactive oxygen species, hypochlorite, peroxynitrite, and chloramines. Oxidative modifications of other amino acid residues require use of strong oxidants, which eventually are produced in the cells. Detailed mechanisms of action of these oxidants is described in subsequent sections of this chapter. 

Ozone is an important natural constituent of the atmosphere,21 being principally concentrated (up to 27% by weight) between altitudes of 15 and 25 km. It is formed by solar uv radiation in the range 240 to 300 nm via the reactions... 

Ozone absorbs uv radiation from 200 to 360 nm. This leads partly to a reversal of reaction 11-2 and thus a steady state concentration is established. The net result of all these processes is absorption and conversion to heat of considerable solar uv radiation that would otherwise strike the earth s surface. Destruction of any signifi-... 

This chapter reviews some of the main topics involved in the design and modeling of solar photocatalytic reactors, with particular emphasis on the authors research experience. Solar photons are source of energy that initiates photocatalytic degradation. Thus, proper consideration of radiative processes is key to address this subject. The determination of the directional and spectral characteristics of solar UV radiation, the interaction of the catalyst with radiation inside reaction spaces, the optical design of solar collectors, and the optical properties of the materials involved are all subjects where these concepts are necessary. Therefore, developments in this area should be solidly grounded on the fields of solar collector optics and radiative transfer, besides the more traditional chemical engineering aspects involved. This requires a multidisciplinary approach. 

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