Ozone and nitrogen dioxide measurements in the framework of the National Integrated Programme for the Control of Forest Ecosystems (CONECOFOR)

Ozone (O3) concentrations were monitored using passive (diffusive) samplers at 20 permanent monitoring plots of the National Integrated Programme for Forest Ecosystem Monitoring (CONECOFOR) during late spring and summer from 1996 to 2000. Nitrogen dioxide (NO2) concentrations were measured at the same sites with passive samplers during the same months in 1999 and 2000. Measurement devices were placed at a short distance from the forest plots in areas with freely circulating air. The exposure period for O3 passive samplers was 1 week; NO2 samplers were exposed for 7 days in 1999 and 14 days in 2000. Mean O3 concentrations recorded by the passive samplers for the monitoring periods in individual years vary from 75.2 to 125.8 μg m-3, showing considerable differences between individual years and the geographical locations of the monitoring sites. Generally speaking O3 concentration levels are higher at the plots located in Central and Southern Italy. The highest mean weekly concentrations were recorded in Sicily with a maximum of 171 μg m-3. No correlation can be found between O3 levels and elevation if all the plots are considered, while a significant increase of O3 levels with elevation can be observed in the six plots located in the Alpine region. The correlation analysis of 5-year mean concentration data and plot latitude show a moderately close relationship. Mean weekly concentrations often exceed 65 μg m-3 as 24 h mean, one of the short term thresholds proposed for the protection of vegetation. Exceedances are recorded in all monitoring periods. At the permanent monitoring observation plot in Sicily this threshold was exceeded in all the years of the study. Mean weekly or fortnightly NO2 concentration levels are generally very low, with the exception of some plots influenced by nearby emissions or transport phenomena. NO2 probably exceeds the critical level for the protection of forest ecosystems at one plot only. No correlation was observed between NO2 and O3 concentration data.