| Popis: |
The ultraviolet radiation (UV) has always been an environmental factor for life on earth. UV is the nonvisible short-waved part of the optical spectrum between 100 and 400 nm wavelength. The sun is the most important source of UV, while the atmosphere depending on the position of the sun, is influencing the intensity of radiation that is reaching the earth primarily by scattering at molecules, water droplets, ice crystals and aerosols as well as by absorption by trace gases, especially ozone, and by reflection on surfaces (Fig. 1). According to its biological effects UV is roughly divided into 3 spectral ranges: UVA, B and C. The wavelengths of UVC ranges between 100 to 280 nm. UVC is the part with the shortest wavelength and therefore the highest photon energy. Due to the effective absorption by ozone in the Hartley band, UV-radiation of a wavelength of less than 290 nm does not reach the surface of the earth with an appreciable amount; a layer of only 0.15 mm of pure ozone can already absorb 99% of the radiation. The average of the total ozone is ranging between 2 and 5 mm. The medium-waved UVB ranges according to the definition of the CIE (1987) between a wavelength of 280 and 315 nm. In the Huggins band, between approximately 300 and 350 nm wavelength, the ozone absorption decreases exponentially with increasing wavelength. This results in a rapid increase of solar radiation in the wavelengths ranging between 290 and 310 nm. Finally, the absorption by ozone has only a small impact on the radiation intensity that reaches the earth’s surface in the long-waved UVA range. |
