The influence of inhomogeneous surface albedo on UV irradiance is investigated for cloud free conditions using a recently developed 3-dimensional radiative transfer model. From the calculations the relative enhancement of UV irradiance due to (partial) snow coverage as well as an 1-dimensional effective albedo is derived. This 1d-albedo is a quantity allowing to account for effects of inhomogeneous surface albedo in 1-dimensional radiative transfer models. The results indicate that the surface albedo must be known on an area with considerable size: even if surface albedo is specified on an area with 40km radius around the measuring site the influence of areas outside this range on UV irradiance can be still up to 3%. Although we already found encouraging agreement between modeled and measured spectral irradiance for clear skies and low surface albedo, the general evaluation of the 3-dimensional model remains an open issue. ¿ 1998 American Geophysical Union