Regional scale risk assessment of ozone and forests

The ozone exposure risk for vegetation in Lombardy (Northern Italy) has been\r\nassessed by the AOT40 exposure index, based on data taken from the existing local\r\nmonitoring networks covering 5 growing seasons (1994 to 1998). One-square\r\nkilometer exposure maps were obtained by using geostatistic techniques (ordinary\r\nkriging) followed by an altitude detrendization of measurement’s temporal\r\nseries to account for the domain’s large topographic heterogeneity. Risk areas\r\n(Level I maps) were identified using a GIS and overlaying the ozone-criticallevel\r\nexceedance maps on the distribution maps of forests and sensitive species.\r\nThe critical ozone exposure level of 10 000 ppb h, adopted by UN/ECE protocols,\r\nis exceeded over the whole Lombardy Territory over the 6-month growing\r\nseason. The highest risk areas are the northwest pre-alpine and alpine belt,\r\ndirectly impacted by the photo-oxidant plume generated by the Milan urban\r\narea. Difficulties met in creating a proper Level II risk assessment for forests\r\nin mountain areas have been bypassed by comparing ozone exposures with summer\r\nclimate features. Soil water availability was assumed not to be a significant\r\nmodifying factor in the mountains of this region because of the frequent summer\r\nrains, whereas the opposite held true for wind ventilation which is generally\r\nweak. Field surveys have reported foliar injuries attributable to ozone in different\r\nspecies of forest trees and shrubs, which provide further evidence of potentially\r\nphytotoxic ozone levels