Spectral solar UV radiation measurements performed at Thessaloniki, Greece (40°N), are presented, and the influence of various atmospheric constituents such as total ozone, cloud cover, and columnar SO2 on these measurements is examined. By comparing UV radiation measurements at days with different total ozone amounts the magnification factor was calculated. Its values range from 1 to 20, depending on the wavelength and the total ozone. A relationship between the UV radiation and the cloud cover was established, being representative only for measurements at 50° solar zenith angle. In addition, the influence of columnar SO2 variations on UV irradiances was also studied. Finally, an attempt was made to compare the relative influence of these parameters on UV radiation, which proved that total ozone is the major factor controlling the solar UVB radiation received at the ground.