Evaluation of pre-industrial surface ozone measurements made using Schonbein's method

Ozone measurements made using Schonbein's method during the late nineteenth and early twentieth centuries have been examined and converted to modern u nits using a method originally developed by Linvill et al. (1980). Monthly Weather Review 108, 1880-1891 and Anfossi et al. (1991). Journal of Geophys ical 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 o f ozone in the presence of water vapour. However, uncertainties in the humi dity correction to the Schonbein reading will lead to considerable inaccura cies in the seasonal cycle established by this method. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.