Ozone data from 19 Italian, Slovenian and Croatian monitoring stations for the years 2000 and after were used to calculate the recently introduced photochemical indicators P1 and P2 during the growth season of 1 April to 30 September (Kovač-Andrić et al., 2009). The results show the highest indicator values for stations from the lower Po river valley and along the northern Italian Adriatic coast. Over the 4-5 years of accumulated data, the average yearly ozone volume fraction remains constant or slightly decreases in the region despite substantial year-to-year fluctuations. An exception is the year 2003 when, with the exception of three southern Italian sites (Sacco, Fontechiari and Ce54) showing a decrease, a strong increase of ozone production of up to 25 % followed by a significant decrease in 2004 occurred (when again at the three above sites slight increases were found instead). For cases when P1 and P2 differ considerably in value, use of the square root of their product is suggested for the rating. A similar but longer-term data analysis from a greater number of existing stations in the region could shed more light into photochemical pollution status over the Mediterranean. @copy; by PSP.

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