The objective of this study was to find out whether the flux approach can be carried out under the routine conditions of the UNECEIICP-Forests monitoring programmes. The ozone (O₃) flux model by Emberson et al. (2000b) was parameterized for beech canopy stands and environmental data were used from Switzerland and Italy. The input parameters for three years (2000-2002) were gathered from the EU/UN-EGE intensive monitoring plots from Switzerland, Italy and Spain. The test for completeness and plausibility resulted in 6 plots (5 within Switzerland, 1 within Italy) out of total 20 possible beech plots. Ozone concentrations were calculated from weekly and bi-weekly passive sampling data. The results of this preliminary study are comparable with the ones produced by Emberson et al. (2000b) for beech canopy stands. The results suggest that the output of the biological more meaningful flux approach identify different spatial and temporal areas and periods as having higher risk to ozone than those identified using the AOT40 approach due to a strong influence of environmental factors such as vapour pressure deficit and soil moisture deficit on the stomata/ ozone flux. For a future extension covering more European countries and different species, the quality and completeness of the input data may be the limiting factor for a complete ozone risk assessment. Furthermore, the scarce data base of canopy gas exchange measurements makes it difficult to validate the model output. In order to define ozone risk on forest ecosystems by the means of a critical flux the estimated model output needs to be compared with possible adverse plant responses such as visible injury or reduced growth.