TREND OF OZONE IN THE FREE TROPOSPHERE ABOVE EUROPE

Ozone observations were made one century ago by the Schonbein techniqu e at meteorological observatories in the alpine region. Within the int rinsic limitations of the technique, historical readings have been con verted to present-time concentrations (p.p.b.v.). The evaluated ozone level in the free troposphere (17 p.p.b.v.) was twice as large as at t he surface; comparable values were obtained by chemical and spectrosco pic technique in the first half of our century. Furthermore, the recon structed ozone trend in the free troposphere shows a sharp increase af ter the '50s, as already observed at the surface at midlatitudes of th e northern hemisphere.