Action 3: Spatial variability of ozone impacts
Mapping by co-kriging
Spatial distributions were developed within the ArcGIS 9.3 software. Ordinary co-kriging on station data and GTOPO30 DEM, for taking into account topographic effects, were carried out and provided the best estimate of the interpolated value. GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of approximately 1 km. GTOPO30 was derived from several raster and vector sources of topographic information. The co-kriging was performed with a Gaussian semi-variogram model with 10 lags, 0.1 lag size, without anisotropy and second order of trend removal for station data. For topography dataset DEM, the geographical distribution was homogenous (regular grids), thus, the co-interpolation, used more neighbors (24 with a minimum of 2). Applying kriging allowed creation of a continuous information layer from a set of individual sample points.
Mapping of AOT40, POD0 and POD1 in 2012 and 2013
Concentrations exceeding 40 ppb (AOT40, Figure 1) and both total stomatal ozone uptake (POD0) and threshold-based phytotoxic ozone dose (POD1) were calculated for 8 Mediterranean forest species (Figure 2, Annex 9) in South-eastern France and across Italy.
Exposure-based critical levels (AOT40) do not include environmental conditions that affect plant responses to O3. The AOT40 was exceeded in the whole domain and the most frequent AOT40 values were calculated between 12 000 and 25 000 ppb. The critical levels of 5000 ppb were exceeded at the majority of the monitored plots in 2012 and 2013. AOT40 is not adequate for forest protection in Mediterranean region. Compared to PODY, AOT40 seems to overestimate O3 risk in Southern Europe. This hypothesis is confirmed when we compared ozone data with damage occurrence. The areas with high AOT40 did not always correspond to the areas with high POD0. In dry area (Mediterranean coastline) the AOT40 values are high, due to higher ozone levels, and PODY are lower. In wet area (Alps mountains) stomata are opened, ozone is absorbed in a continuous way and we can observe high PODY.