[understanding and radiation hygiene assessment of solar UV exposure in Germany].
In order to monitor the natural ultraviolet (UV) radiation and to assess it from the point of view of radiation hygiene, the Federal Office for Radiation Protection (BfS) and the Federal Environmental Agency (UBA) have built up a common network for UV monitoring. Since 1993, the ground-level solar UV radiation has been measured at four sites in Germany every 6 minutes, with spectroradiometers in the wavelength range between 290 and 400 nm. Because erythema (sunborn) is of special interest in terms of radiation hygiene, the erythemal weighted irradiance was used as a measure for the biological effect of UV exposure. For this purpose, the measured spectral irradiance was multiplied by the relative erythemal weighting function, and the resulting function integrated from 290 to 400 nm. In the summer months of June and July 1999, the erythemal irradiance exceeded regularly the value of 175 mW/m2 in the south of Germany. In the north, values of not less than 160 mW/m2 were measured during this period. These values correspond to an UV index of more than 7 or 6, respectively--a high exposure regarding to the classification of the German Radiation Protection Commission (SSK), for which (absolute) sun protection is recommend. Between 1995 and 1999, the four sites were characterized by a small increase of the ground-level UV exposure of approx. 10%. Nevertheless, in consideration of the manifold factors affecting the acquired data, the measuring period of 5 years is still insufficient to demonstrate an ozone-dependent effect.