| Summary: | <p>Ozone measurements are performed since 1996 at the Permanent Monitoring Plots (PMPs) of the National Integrated Programme for Forest Ecosystem Monitoring (CONECOFOR). Weekly ozone concentrations are determined by passive samplers during spring and summer months, over a time period of 10 yrs. We analyzed data collected over a time period of ten years. Ozone shows potentially phytotoxic concentrations especially at the plots located in the central and Southern regions. Although monitoring periods at the different plots are not homogeneous, statistically significant differences between yearly concentrations of subsequent years were observed, highlighting a considerable temporal variability of ozone pollution levels. Trend analysis performed on ten years data series points out an increase of ozone concentrations over the considered time period at seven plots, all located in central and Southern Italy. The same analysis performed on data collected during the vegetative period (April - September) at the different PMPs from 2001 to 2005 shows significant positive trends at 5 plots, three of them located in the Alpine region, and 2 in Southern Italy.</p>
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