HIGH OZONE EPISODE AT ZAVIŽAN CROATIA DURING 17–19 JULY 1998

Abstract: We investigated an unusual elevated-ozone episode that took place at a high altitude measuring site Zavižan (44.817°N, 14.983°E, 1594 m a.s.l.). The episode was characterized by three consecutive peaks. The first one was the highest (over 120 ppbv), and it occurred at the late night on 17 July. Following two (both about 110 ppbv) appeared approximately 18 and 36 hours after the first peak, respectively. The night-time maximum and the departure from the usual diurnal variation of ozone concentration during investigated episode point to the non-local pollution sources, rather than to local photochemical production. Thus, recorded ozone peaks might arise due to the long-range transport of photo-oxidants; 2) stratospheric ozone intrusion; or 3) they might be result of both (1) and (2). In order to inspect which of above,processes is responsible for the increased ozone concentrations we applied,the unified EMEP model, which among others, simulates atmospheric transport and deposition of photo-oxidants, and, a mesoscale numerical weather prediction model WRF-ARW V2.2. Additionally, the larger scale atmospheric conditions were examined based onthe,ECMWF ERA-40 reanalysis fields. Results suggest that the stratospheric ozone intrusion played an important ,role in the occurrence of investigated episode. Key words: ozone episode, stratospheric ozone intrusion, long range transport, EMEP model