Increases in tropospheric ozone due to photochemical production, mostly due to growing industrial and technological NOx-emissions, in the industrialized northern hemisphere can overcompensate for increased UV-B radiation resulting from ozone depletions due to chlorine-catalyzed reactions in the stratosphere. This is especially the case in the summer months, because during this period a large fraction of the UV, which reaches the surface as diffuse radiation, is scattered by air molecules, droplets and aerosol particles in the troposphere. This causes a relatively longer path through tropospheric than through stratospheric ozone. Analyses using calculated, as well as observed ozone profiles at the station Hohenpei&bgr;enberg in Bavaria, FRG, show, that decreases of UV-B radiation at the earth's surface are possible even when total ozone declines. ¿ American Geophysical Union 1989