Ozone risk assessment for European forests: a ten-year study on permanent monitoring plots

Ground level ozone still poses a serious threat to forest ecosystems across Europe and represents a priority for the UNECE Convention on Long-range Transboundary Air Pollution. The ICP Forests Expert Panel on Ambient Air Quality has coordinated the monitoring of ozone concentration and effects (i.e. foliar injury on native vegetation) since 2000 on an annual basis on intensive long-term forest monitoring sites across Europe (Level II). Methodologies, including quality assurance such as data harmonization, completeness and plausibility tests have been applied according to the ICP Forests Manual, parts X and XV (Schaub et al. 2010a & 2010b). Here, the authors evaluate the available data on ozone concentration, exposure, and foliar injury that have been collected at the very forest sites across Europe from approx. 80 – 150 plots and over 1’000 native species. Emphasis will be put on European scale analyses for i) spatial and temporal trends for ozone concentration; ii) different AOT40 assessment methodologies; iii) comparison between measured concentrations with passive samplers, respective AOT40 estimates and modeled EMEP outputs; and iv) foliar injury occurrence in relation to ozone concentration and ozone exposures respectively. Considering stress factors such as drought and physiological response indicators, these analyses will favor a comprehensive evaluation of ozone risk for European forests based on data from the very forest sites. Furthermore, these harmonized data sets will serve as a valuable basis for further integrated analyses and validation of models, such as from EMEP.