Inga Lisac

An analysis of surface ozone data measured at the end of the 19th century in Zagreb, Yugoslavia

A 12-year record of surface ozone data collected by means of Schoenbeins method in Zagreb, Croatia, Yugoslavia, 1889-1900 is analyzed and calibrated. The data were collected twice a day. To convert the original data into absolute units the Montsouris regression modified by Bojkov has been used. The statistical parameters of daytime and night-time data samples show a significant difference. The annual run of daytime data contains a primary maximum at the transition from spring to summer and a secondary at the beginning of autumn. The annual run of night-time values contain one maximum only, situated at the transition from spring to summer. A comparison of old ozone data (1893 1900) with present ozone measurements over a 5-month warm period (1975), shows an increase of volume fractions from 36 to 67 ppb for daytime and from 30 to 56 ppb for night-time. It should be taken into account tha, t many uncertainties exist in the data. Key word index: Surface ozone, 19th century ozone observations, daytime and night-time 0 3 data, historical ozone data, seasonal ozone cycle.