Evaluation of pre-industrial surface ozone measurements made using Schönbein’s method

Ozone measurements made using Schönbein’s method during the late nineteenth and early twentieth centuries have been examined and converted to modern units using a method originally developed by Linvill et al. (1980). Monthly Weather Review 108, 1880–1891 and Anfossi et al. (1991). Journal of Geophysics Research 96, 17,349–17,352. New data are presented here from sites in Europe, Asia, Africa, Australia, and South America. The values obtained lie in the range 5–15 ppb for all sites. A negative correlation between ozone and humidity is observed, which may be consistent with photochemical loss of ozone in the presence of water vapour. However, uncertainties in the humidity correction to the Schönbein reading will lead to considerable inaccuracies in the seasonal cycle established by this method.