On changes of spectral UV-B in the 90ʹs in Europe Original Research Article

The variability of solar irradiance in the UV-B spectral region is studied at two European stations, Thessaloniki, Greece (40.5°N) and Uccle, Belgium (50.8°N), operating well calibrated spectroradiometers during the period 1990–97, which is the longest available clear sky time series of spectral UV-B data. Solar spectral irradiance at two distinct wavelengths is used in the presented analysis, the strongly ozone dependent 305nm and the weakly dependent 325nm. It is quantified in this study to what extend total ozone is controlling long-term changes of solar irradiance below 315 nm at ground level. This is supported by the similar long-term variability under clear sky and all sky conditions during the past seven years. It was found that the increase in UV-B solar irradiance, which can be attributed solely to the observed ozone decrease of 4.5% per decade, is of the order of 10% per decade at 305 nm, 63° SZA. The increase found at 325 nm is associated with the observed decreases of various air pollutants in the area, as it appears from the long-term columnar SO2 measurements. The observed changes in solar irradiance (in % per year) are verified with model calculations performed with a radiative transfer model.