1Academy of Athens, Navarino Environmental Observatory, Biomedical Research Foundation, Greece
2Biomedical Research Foundation of the Academy of Athens, Athens, Greece
3Department of Physics, University of Thessaloniki, Greece
4Faculty of Geology and Geoenvironment, University of Athens, Greece
5Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Greece
6Meteorological Observatory Lindenberg, German Meteorological Service, Germany
7Climate Change Unit, Finnish Meteorological Institute, Helsinki, Finland
Abstract. This study examines the UV variability at 305 nm and 325 nm over selected sites in Canada, Europe and Japan. Site selection was based by the availability of UV spectroradiometric datasets longer than 15 yr. The analysis of UV variability was conducted in combination to total ozone, aerosol optical depth and cloud variability. The results suggest that the period with the longest available spectral measurements of UV irradiances over Canada, Europe and Japan can be divided into three sub-periods of scientific merit: the first period is the period perturbed by the Pinatubo volcanic eruption for which it is shown that excess volcanic aerosol might have enhanced by an additional 6% the "conventional" (+18%) amplification factor of UVB at ground level. The second period is characterized by a UVB increase caused by the synergy of ozone decline and tropospheric aerosol decline (brightening effect) during which overhead cloudiness remained without statistically significant trends. During this second period, the long term variability is the brightening of +0.94% yr−1 and +0.88% yr−1 at the wavelengths 305 nm and 325 nm respectively. The third period, which refers to the last 4–5 yr, might provide for the first time significant statistical evidence indicating the slowdown of the upward trends observed before, over the sites studied where UVB sites seem to have passed maximum UVB exposure levels since about 2006.