Ultraviolet radiation (UVR)

Ultraviolet radiation (UVR) during passage through the layer of ozone in the stratosphere mostly absorbed by ozone, so the UVA and UVB rays that reach the earth's surface becomes less. UVC photolysis interact with oxygen produces ozone. this is because the biological effects of ultraviolet B radiation is greater than ultraviolet A radiation, so the concentration of pan environmentalists and environmental epidemiology is devoted to observing UVB from time to time, although the percentage of ultraviolet A radiation is much higher when compared with a ratio of 95% UVB and 5%. Ultraviolet radiation reaches the earth's surface depends on latitude, altitude and the presence of cloud or aerosol particles. Area near the equator, have the highest intensity when compared to the northern and southern hemispher. The presence of clouds and air pollution (in the form of smoke or water vapor particles), can lower the UVB. The influence of clouds on the irradiation of the spiral can be approximated by a factor F: F = 1 to 0.056 C.

C is the total cloud index which ranges between 00-10. Value of 10 for thick clouds covering the sky completely. For dense clouds, ultraviolet radiation down to 44% for direct radiation. The estimated reduction in ultraviolet B radiation (UVB) because the cloud based on satellite measurements of backscattering with UVB which is 30% at 60 ° latitude, 10% at 20 ° and 20% on the equator. The relative intensities of ultra-violet B radiation from time to time is not fixed, the maximum at noon (12.00) and minimum in the morning and afternoon (at 06.00 and 19.00).

European population is estimated to have exposure to UVB radiation ranges between 210-390 MED, depending on the type of work (outside / inside the room).

The estimated annual doses of  UVB from some activities

Activities	Annual doses of  UVB (MED)
Working outdoors (including exposure of on the weekend) Working indoors (including exposure of on the weekend) 2 weeks vacation in the Mediterranean Sunbathing on the beach 15 hours	270 90 100 20