The scope of this paper is to provide an exptl. and modeling contribution on the role of suspended lower tropospheric particles to the UV spectral irradiance reaching the ground in urban environments. The UV spectral irradiance was measured with a UV spectrophotometer, while the aerosol data were obtained simultaneously by a lidar system operating in the 300 nm spectral region. Both UV and lidar instruments were operated inside the Athens basin during various air pollution and meterol. conditions, in the frame of the European MEDCAPHOT-TRACE Campaign in summer 1994. Aerosol vertical profiles were also obtained by a second lidar system operated outside the Athens basin (in a sub-urban area) during the same time period and were intercompared to the urban profiles. Using the lidar data as input to a radiative transfer model (MODTRAN), we provide comparisons of measured and modeled spectral UV irradiances under distinct environmental conditions.