SURFACE OZONE AT MID LATITUDES IN THE PAST CENTURY

Surface ozone observations were made from the second half of the past century up to the first decades of the present century at many observa tories in the world using the Schonbein technique. Although there are some uncertainties about that technique and on possible interferences, accurate readings can be converted to present-time concentrations (p. p.b.v.). The analysis of data series gathered at some sites at mid-lat itudes of the Northern and Southern hemispheres leads to the conclusio n that a century ago the mean ozone level was about 10 p.p.b.v., the s easonal course changing in relation with local climatology. From that time anthropogenic emissions have increased the ozone level, more at N orthern than at Southern latitudes.