Quantifying the fine scale (1km x 1km) exposure, dose and effects of ozone. Part 1 Methodology and application for effects on forests

Surface ozone concentrations show very large local variability. This, in rural areas, is largely a consequence of the degree to which the surface air is decoupled from the bulk of the atmosphere by nocturnal and winter stability effects and of the aerodynamic roughness and topography of the countryside. Procedures have been developed to simulate these effects and have been used with O3 data from a regional monitoring network to quantify exposure of vegetation to mean and peak O3 concentrations. The index of exposure to potentially phytotoxic O3 concentrations is the AOT40 (accumulated exposure over a threshold of 40 ppb) expressed in ppb.h. The accumulated exposure of crop and forest surfaces to ozone is shown to increase approximately linearly with altitude and along a gradient from 3000 ppb.h in north west Scotland to 7000 ppb.h in the south of England. The area of UK forest which exceeds the critical level for ozone effects (104 ppb.h above 40 ppb) totals 2.0 × 104 km2 and represents 47% of afforested land. The areas affected include most of southern and central England and Wales and large plantation forests of Northumberland and the Scottish borders.