The relation of the daily doses of erythemal UV at Uccle with total solar irradiation, total ozone column and the aerosol optical depth in the UV are investigated together with trends in these atmospheric parameters for the period 1990 to March 2007. It is shown that the trend in UV radiation is negative in January, August and December and positive the rest of the year. The correlations with total solar radiation, total ozone and aerosol optical depth at 320 nm are in the range of 0.90 to 0.99,-0.2 to-0.5 and-0.0 to-0.3, respectively. However the UV daily dose changes with up to 1.5% for a 1% change in total solar radiation, with -0.8% for a 1% change in aerosol optical depth and with only-0.1% for a 1% change in ozone, indicating the importance, on the short time-scale, of changes in aerosol properties for the UV irradiance reaching the surface.