Ozone concentrations are decreasing but exposure remains high in European forests

Ozone is a gaseous air pollutant present in remote areas at levels causing visible symptoms in plants. Despite a significant reduction, ozone levels at ICP Forests sites still exceed the threshold value fo r adverse effects. Ozone-induced foliar symptoms have been observed on woody plant species all across Europe. Further observational and long-term monitoring studies are needed to better quantify dose-response relationships and a potential impact on forest growth