UV-C radiation

Fig. 3.9. Photochemical formation and non-catalytic destruction of ozone. UV-C radiation (200-280 nm wavelength) UV-B radiation (280-320 nm wavelength). Note how high-quality energy (UV radiation) is converted into lower quality energy (heat). Catalysts such as freons or nitrogen oxides can destroy ozone (e.g. Cl + 03 —> CIO + 02).

For disinfection and oxidation purposes, UV-C radiation is normally used although the application of other types of UV radiation has also been reported in the literature [10]. For example, the use of UV-A or even visible radiation to treat natural organic matter present in surface water has been reported with and without the presence of catalysts [82,83]. Concerning the utilization of UV-C radiation, the most common use is 254-nm radiation due to the development of low-pressure vapor mercury lamps by Hewitt in 1901 [13]. For this reason, in this chapter the information presented mainly focuses on the use of 254-nm UV-C radiation. 

In another example [229], atrazine and one of its main by-products (deethylatrazine) have been removed in a large-scale 03/UV plant. The plant was fed with 70 m3 h 1 of groundwater (pH 7.2, 464 mg L 1 bicarbonate and 0.6 mg L-1 DOC). UV-C radiation was emitted from a medium-pressure mercury arc lamp with a maximum total electrical power of 10 kW and 1.2 kW maximum radiant power in the UV-C region. The maximum electrical power of the ozone generator was also 10 kW. Concentrations of atrazine and deethylatrazine in the plant inlet were 0.28 pg... 

Thus, these processes remove the most energetic UV-C radiation from the atmosphere and convert it into thermal energy. 

The most important atmospheric photoreagent is, however, molecular oxygen it absorbs UV-C radiation within 100-240nm, with a maximum at 160nm, and undergoes photodissociation to the O atoms in their ground states 0(3P) ... 

Absorption of UV-C radiation by cellular constituents of organisms may lead to severe cell mutations and cell death. Therefore, this wavelength band is often called the germicidal range. It is used in UV disinfection processes to inactivate bacteria, viruses and other microorganisms (cf Chapter 9). At the Earths surface sunlight contains no VUV and UV-C radiation because of their efficient absorp-... 

The technology of UV disinfection of water and air is based on the direct irradiation of the media, mostly in homogeneous aqueous or gaseous phases. It is weU established in industry, and monochromatic LP or polychromatic MP mercury lamps as sources of UV-C radiation are apphed (cf. Schneider et al., 2001, Kalisvaart, 2001). 

For example, the direct photolysis of trichloroethene in air with UV-C radiation (using a xenon flash lamp) initially produced dichloroacetyl chloride ([CI2HC-COCl] >90%) that subsequently was photooxidized to yield phosgene ([Cl2C=0] < 25%), trichloroacetyl chloride (TCAC, [CI3C-COCI] < 2%), unidentified intermediates, and ultimately HCl and CO2 were produced (Haag et al., 1996). In this connection, it is relevant to stress that dichloroacetyl chloride is 40 times more toxic than trichloroethene (cf. Haag et al., 1996). 

UV radiation from the Sun is a ubiquitous and important source of DNA damage that contributes to the high incidence of skin cancer in exposed individuals. The UV radiation spectrum has been arbitrarily divided into the UV-A component (wavelengths 320 00 nm), the UV-B component (wavelengths 295-320 nm), and the UV-C component (wavelengths 100-295 nm). Penetration of the atmospheric ozone layer is weak for wavelengths below 300 nm. Thus, solar UV radiation primarily comprises the UV-A and UV-B components. However, experimental studies typically involve the use of UV-C radiation from germicidal lamps with a sharp emission maximum at 254 nm. Since... 

Some of the dangerous radiation removed in the stratosphere is absorbed by the O2 molecules there. Radiant-energy wavelengths must be shorter than 242 nm to have enough energy to break the 0-0 bond, and UV-C radiation has wavelengths in the proper range. 

Explain why we are fortunate that UV-C radiation is almost completely filtered out by the gases in the atmosphere. 

UV-C radiation has wavelengths less than 280 nm while UV-B radiation has wavelengths between 280-320 nm. Which is higher in energy ... 

When CFC gases are released into the atmosphere, they gradually rise into the lower stratosphere because they are not washed out of the troposphere by rain. In the stratosphere the chlorine atoms are released when the CFC molecules are broken up by energetic UV-C radiation as indicated by the reaction ... 

UV-C radiation that reaches the surface. The problan is especially acute in Antarctica during the early spring in October. 

A xenon arc (ORC 10OOW lamp) was used from which infrared and UV-C radiation were filtered out. To remove UV radiation (0.035 mW cm 2) a polycarbonate screen was placed in the light path leaving only photosynthetically active radiation (PAR)(160 pE m 2 s ). 

Ozone molecules (see p387) are produced in the upper atmosphere through the action of UV-C radiation (light with a wavelength less than 242 nm) on oxygen gas. 

Distinguish among UV-A, UV-B, and UV-C radiation. Why does UV-B pose the greatest danger in the troposphere ... 

HlavataL, Bankova K, Vyskocil V, Labuda J (2012) Evaluation of damage to DNA induced by UV-C radiation and chemical agents using electrochemical biosensor based on low molecular weight DNA and screen-printed carbon electrode. Electrochim Acta 71 134-139. doi 10.1016/j.electacta.2012.03.119... 

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