Comparisons of satellite derived UV estimates with ground-based measurements showed that in most cases satellite retrievals overestimate UV radiation. Considerable differences were usually found over Europe, while the smallest were reported over unpolluted and aerosol-free sites. According to recent studies, satellite bias increases with increasing aerosol load, indicating the weakness of the satellite measurements and processing algorithms to account correctly for aerosol absorption in the atmospheric boundary layer. Recently, a new satellite instrument named OMI (Ozone Monitoring Instrument), for measuring ozone, UV radiation and columns of various species (like aerosols, trace gases, etc) has been launched on board the AURA satellite. The aim of this project is to validate and explain possible errors in products derived from OMI, using synchronised high quality ground-based measurements of spectral UV irradiance and aerosol properties combined with model sensitivity studies over an urban site. The effects of temporal and spatial variability of aerosols in the vicinity of the site will be also investigated, using measurements of aerosol properties and UV radiation at a nearby location.