Ozone presents difficulties. It is an important issue which may grow in importance in the future if, as anticipated, concentrations rise, but the only acceptable way of monitoring it at remote locations, without a power supply, is diffusion tubes. These have been used in the ICP Forests Level 2 programme, but do not give values for peak ozone incidents, which are believed to cause visible ozone symptoms. Vegetation change in plant communities has been shown to be related to the AOT40 exposure index, which cannot be derived directly from diffusion tube data, and studies would be needed.
