UV-A radiation

Franklin LA, Krabs G, Kuhlenkamp R (2001) Blue light and UV-A radiation control the synthesis of mycosporine-like amino acids in Chondrus crispus (Florideaphyceae). J Phycol... 

Observations Azo intermediates that effectively absorb ultraviolet A (UV-A) radiation... 

UV radiation comprises energies from about 300 kJ Einstein-1 (UV-A radiation, 1 einstein= 1 mol of photons), up to 1200 kJ Einstein-1 (vacuum UV). Table 6 shows the wavelength and energy of dilferent UV radiation types. 

Products of these reactions, aldehydes and ketones, undergo photodissociations under tropospheric sunlight. Aldehydes absorb actinic UV-A radiation and methanal absorption extends out to approximately 370 nm, whereas the heavier aldehydes absorb only to approximately 345 nm. Methanal has two photodissociation paths ... 

Nanostructured Ti02 particles (particle size 5-50 nm) are used as sunscreens in the cosmetic industry. Nanosized Ti02 is an effective absorber of UV-B (280-320 nm) and UV-A radiation (320-400 nm). Because ofits small particle size, itappears transparent [2.70]. Intensive research work is in progress worldwide aimed at utilizing the photoactivity of Ti02. Titanium dioxide catalyzes the decomposition of organic compounds in wastewater [2.71]. 

One of the first researchers to report the mapping of a photostability chamber was O Neill (42). His map (Fig. 34) shows the uneven distribution of UV-A radiation in a tabletop, long-arc, xenon unit and the VIS distribution in a Hotpack Low Temp Light Cabinet (Fig. 35). Both of these figures clearly illustrate the uneven distribution of radiation in these chambers. 

Figure 40 is the map of the UV-A radiation obtained when four and seven T-5, full-spectrum lamps are used in two different test chambers. There is a significant difference in the two maps obtained. 

Habib and Asker (68) showed that metronidazole solutions decompose more under artificial sunlight [from two 40 W fluorescent sunlamps and fluorescent radiation (from cool white tubes)] in a Atlas HPUV Actinic Exposure Cabinet, than under UV-A radiation, as shown in Table 4. 

The photostability of sunscreens has been, since the 1990s, primarily a UV-A issue due to the fact that no agreed method was (and still isn t at this time) available to assess the protective capacity of a sunscreen preparation towards UV-A radiation. As in the early days, the photostability of the UV filter or the sunscreen preparation itself was tentatively used instead of a skin-related end point. 

One may ask if EHMC is suitable for stabilizing BM-DBM. It has molecular features similar to the previously discussed three UV-B sunscreens and an acceptable triplet energy of 57kcal/mol (27). In fact, EHMC does stabilize BM-DBM when the mixture is exposed to UV-A radiation only (>340 nm). This is another proof that the stabilization is not due to a shielding effect. EHMC does not absorb any radiation under these conditions (Gonzenbach H and Berset G, personal communication, 1999). 

Figure 11. Ratio of global radiation fluxes (normalized to cloudless conditions) for erythemal radiation, UV-A radiation and total solar radiation in dependence on cloudiness, separated for cases when the sun is free or when the sun is totally covered by clouds. Bars indicate -t- 3 standard deviation of the mean.

Figure 6. Absorption plots for UV-A radiation (plot A) and spectra at 50% UV penetration depth (plot B) for PAH-contaminated site in St. Louis Bay, Duluth, MN and a near-shore location in Lake Superior. The 50% penetration depths shown are 10 cm and 80 cm for the St. Louis Harbor and Lake Superior sites, respectively.

Diamond et al. [127] have estimated UVR doses in wetlands using this approach. Typical UVR doses were estimated by first generating maximal solar radiation doses for each day using a radiative transfer model, SBDART [113]. The model produced values for the full spectrum of solar radiation, from 280 to 700 nm, for cloudless conditions. These maximal values were then modified based on cloud cover effect estimates from 30 yr of historical solar radiation data (National Renewable Energy Laboratory, Department of Energy http //rredc.nrel.gov/solar/). The values derived in this procedure were estimated daily terrestrial, spectral (2 nm increments from 280 to 700 nm) solar radiation doses. Water column doses were then derived from absorption coefficients and spectral attenuation data described by Peterson et al. [128]. Although the focus of this effort was to characterize risk of UV-B radiation effects in amphibians, the procedure is directly applicable to phototoxicity, and the resulting UV-A radiation and spectral doses could be directly incorporated into calculation of possible effects. 

E.L. Bass, S.N. Sistrun (1997). Effect of UV-A radiation on development and hatching success in Oryzias latipes, the Japanese medaka. Bull Environ. Contam. Toxicol, 59, 537-542. 

The sensitivity of man, animals and plants to UV-B and UV-A radiation is of special importance. Possible effects are, for example, growth changes or a decrease in harvest crops (photosynthesis disruption), tumor indications (skin cancer and eye diseases) and the decrease of sea plankton, which would affect the food chain. One side-effect of ozone depletion is the warming up of the earth s surface. 

Explain why it is beneficial to humans for UV-A radiation to reach the surface of the earth. 

Dovrat, A. and Weinreb, O. (1999) Effects of UV-A radiation on lens epithelial Na,K,ATPase in organ culture, Invest. Ophthalmol. Vis. Sci., 40, 1616-1620. 

De Filippis, P, Bovina, E., Da Ros, L., Fiori, J., and Cavrini, V., (2002) Photodegradation studies on lacidipine in solution basic experiments with a cis-trans reversible photoequilibrium under UV-A radiation exposure, J. Pharm. Biomed. Anal., 27, 803-812. 

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