Evaluation of European-wide map creation of flux-based ozone indicator POD for selected tree species


Ozone in the atmosphere significantly alters agricultural and forestry production in terms of yield and quality. These effects are quantified under European regulations (Directive 2008/50/EC) by an indicator of cumulative annual ozone levels over a given period and above a given threshold: the AOT (Accumulated Ozone over Threshold). However, this indicator does not take into account plant phenology and climatic factors such as water stress (often concomitant with ozone pollution peaks), which leads the plant to reduce its stomatal flux and therefore its exposure to ozone. For this reason, the use of the AOT indicator is not sufficient to develop satisfactory dose-response relationships, introducing significant uncertainties into the assessment of the impact of ozone on agricultural yields.
To overcome this shortcoming, an indicator based on stomatal fluxes (phytotoxic ozone dose, POD) was proposed in the 2000s by the "IPC-Vegetation" expert group, which works in support of the Geneva Convention's Working Group on the Effects of Long-range Transboundary Air Pollution (LRTAP), in conjunction with the Working Group on Effects (WGE) and the European Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants (EMEP). Ineris has recently developed a tool for modeling this phytotoxic dose of ozone using data from air quality modeling or measurements. This tool has been used by the Health/Environment Topic Centre in support of the European Environment Agency for several years, to produce POD indicator maps for several agricultural species published in the Agency's air quality reports.
The work presented in this new study includes a mapped POD index calculation for beech (Fagus sylvatica) and spruce (Picea abies) species. This new tool follows the methodology by the working group ion effects of the Convention on Long-range Transboundary Air Pollution. In conclusion, the critical loads (or significant impact thresholds) for the POD indicator, for beech and spruce, were exceeded in a large part of the European area considered, with the exception of large areas in Northern Europe for spruce and more local areas in different countries for both species.