Intensity of UV radiation

Apart from a few applications, such as UV disinfection and lacquer hardening, the intensity of UV radiation is well below that of visible light in ambient daylight or indoor lighting. A UV sensor must therefore be insensitive to visible light, otherwise the detection signal would easily be drowned out by the visible fraction of the radiation spectrum. Sensors that fulfill this requirement have a selective spectral sensitivity in the UV range. There are two important selectivities, known as visible-blindness and solar-blindness. 

In addition to H2O2 (e = 18.61VT1 cm-1 at 254 nm), other species can absorb photons at these short wavelengths, and can act as light filters. However, if the contaminants can be directly photolyzed, this may improve the efficiency of the oxidative destruction process. As the intensity of UV radiation decays exponentially towards the bulk of the solution, it is necessary to establish conditions of turbulent flow to continuously renew the solution surrounding the luminous source. 

Robinson and Robbins (1970) think that these processes are effective mainly in the stratosphere. This concept is reasonable since O concentrations in the stratosphere are greater than in the troposphere. Furthermore, the intensity of UV radiations is also greater above the tropopause. According to Ehhalt et al. (1977) the flux of N20 from the troposphere to the stratosphere is between 6 x 108 and 30 x 108 molecules cm 2 s 1 which are equivalent to (7-35) x 1061 yr ". These values are based partly on the N20 concentration gradient measured in the lowest three kilometers of the stratosphere and partly on the net transport coefficient of 1 x 103 cm2 s 1 and... 

Table III, preferential use of 10- m films to study changes in methyl group concentration might be recommended. However, the optical model presented here assumes that the concentrations of the IR-absorblng species are uniform throughout the film. Therefore, If the bulk concentrations predicted by the optical model are to be valid throughout the film, degradatlve reactions should occur uniformly throughout the film. For reactions influenced by the metallic substrate, this requirement will obviously be met better by thinner films. Also, for photochemical reactions to yield degradation products that are distributed uniformly throughout the film, the Intensity of UV radiation throughout the film must also be uniform. This condition likewise will be most nearly approximated In thin films.

The LDPE foils were placed in the glass vessel in the atmosphere of saturated vapors of phosphoryl chloride. The sorption of the UV sensitizer onto the surface of the PO foils took 24 hours. The foils were then irradiated by UV radiation in an open quartz tube having a diameter of 50 mm. The UV light with a wavelength X = 366 nm was emitted by a 400 W mercury discharge lamp. The distance (d) of the UV tube from the surface of polymer varied between 50 and 200 mm. The relative intensity of UV radiation is inversely proportional to the square ratio of the UV source distances according to the relation ... 

The deterioration of the stratospheric ozone layer over Antarctica permits excessive amounts of solar nltraviolet radiation (UV) to reach the surface of the continent (Appendix 2.11.5). The increase in the intensity of UV radiation in Antarctica affects organisms on land and in the oceans as described in a book edited by Weiler and Penhale (1994). A summary by Graedel and Crutzen (1993) of the health effects of UV radiation indicates that it causes skin cancer in light-skinned individuals. Studies referred to by them indicate that a 1% reduction in the inventory of stratospheric ozone increases the effective UV dose by 2%, which causes a 4% increase in the incidence of the basal-cell carcinomas and about a 6% increase in the incidence of squamous-cell carcinomas. Therefore, unless special precautions are taken, geologists and other people who usually work out-of-doors in Antarctica during September and October may be exposed to higher doses of UV radiation than persons elsewhere on the Earth. The energy spectrum of solar UV radiation is discussed in Appendix 2.11.3. 

Materials used in external parts of an aircraft are exposed to very demanding conditions such as veiy low pressure, a large temperature variation within a short period of time, a large amount of stress, UV, an influence of aggressive chemical liquids. Materials used in spacecraft are exposed to still higher temperature changes, intensity of UV radiation,... 

In the upper stratosphere, at an altitude of about 40 km, this same reaction proceeds with a rate constant of 1.0 x 10 s h (The difference is caused by the higher intensity of UV radiation at higher altitude.) If an experiment were to simulate these conditions, how long would it take for an initial ozone concentration of 5.0 mM to fall to 2.1 mM ... 

The detailed results of the photochemical models are dependent on the adopted UV radiation field as well as on the photodissociation and photoionisation cross-sections, which in principle can be obtained by laboratory or theoretical studies, and on the nature of the dust particles for which the chemical composition, size and hence optical properties are poorly known. In the absence of definitive information, detailed models of the photochemistry have relied on some rather simplistic approaches to the radiative transfer of UV photons through the envelope. Nejad and Millar (1987,1988) have used the approach developed by Jura and Morris (1981) which assumes that the dust grains absorb but do not scatter and leads to a numerically simple equation for the intensity of UV radiation at any point in the envelope. On the other hand, Glassgold and co-workers have used a formalism devised by Gerola and Glassgold (1978) in which the scale-length, dp for photodissociation of any species is used to diminish the intensity incident on the CSE, that is, the intensity is reduced by a quantity exp(-d(/r). These authors have also included the effects of both continuum and line self-shielding in their calculations. 

New technologies provide commodity PO with modified sensitivity to degradation. Depletion of the ozone layer accounting for a potential increase in the intensity of UV radiation should be anticipated by relevant UV stabilizers. Effective radiation-resistant protection during and after sterilization by energetic radiation is necessary. 

Intensity of UV radiation is measured in radiometric units (Tables 10.1,10.2), whereas the intensity of visible light is measured in photometric units (Table 10.1) by radiometers [1762] ... 

Photochemical reaction rates are increased by increased intensity of UV radiation, which is in turn caused by depletion of stratospheric ozone due to the release of fluorocarbons and other man-made chemicals [34]. 

Comparison of the experimental integral kinetic curves and their differential anamorphoses of photoinitiated copolymerization of HDDA -TGM-3 system depending on its composition and intensity of UV radiation (a) and the corresponding calculated kinetic curves (b) is shown in Figs. 2-4. 

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