Since clouds and aerosols contribute substantially to the attenuation of biologically effective UV at ground level it is important to consider their role in studies on UV climatology on earth. We describe a method to quantify this attenuation using spectral measurements of UV radiation at ground level and measurements of total solar radiation. The analysis presented gives a very good indication for a nonlinear relation between the attenuation of biologically effective UV on the one hand and total solar radiation on the other. An UV-climatology can be calculated using the relations found. ¿ American Geophysical Union 1995