A 26‐year (1868–1893) data series of daily ozone readings performed at Moncalieri, northern Italy, by the Schönbein test paper technique has been analyzed. The availability of a series of simultaneous readings by the Schönbein and a quantitative technique (Levy, 1877) and the conversion chart for humidity by Linvill et al. (1980) allowed us to develop a procedure to convert the Moncalieri data into parts per billion by volume values. The results seem to indicate that in comparison to one century ago, the ozone level in Europe has increased by more than twice not only at the surface but also in the free troposphere.
Records of surface ozone data collected twice a day by means of the Schönbein method at Villa Colon, Montevideo, Uruguay, during the years 1883–1885 and at Cordoba, Argentina, during the years 1886–1892 have been converted to present‐day concentrations. Most of the uncertainties suffered from the original technique are removed by a two‐step procedure, in particular a conversion algorithm for humidity and a linear regression constructed by simultaneous readings of Schönbein and a quantitative method. The relative error of this procedure, previously applied to the Moncalieri data series, is 33%. Within these limitations we can state that one century ago the surface ozone levels at that latitude of the southern hemisphere were comparable to those of Moncalieri and Montsouris. Furthermore, the recent levels observed in remote areas at that latitude are approximately twice as large as a century ago.
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