This was consistent with the exceedance of the concentration-based critical level of ozone ( O3 ) for agricultural crops and ( semi- ) natural vegetation ( dominated by annual species ) at 80 % of the monitoring sites . ICP Vegetation , in collaboration with the EMEP Meteorological Synthesizing Centre - West ( MSC-W ) , updated exceedance maps of critical O3 levels using concentration- and flux-based methods to calculate critical O3 levels for wheat and beech .