Ozone measurements have been apart of EMEP since its third phase in 1984–1986 and since 1988 data have been collected systematically. By 1992 data for 76 sites were being collected by the Chemical Co-ordinating Centre in NILU. The mean ozone concentration increases from 20–25ppb in the western and northern fringes to 30–35 in central areas of Europe. There is also evidence from the last decade of an upward trend of up to 0.5ppb y–1 at rural sites in the UK. The data have been analysed to estimate the spatial patterns in AOT 40 for ozone effects on crops and forests. The data show that the critical level for cereal crops of 5300 ppb.h above a threshold of 40 ppb is exceeded over almost all of continental Europe south of 65°N and over most of S.Britain. A similar exercise for the AOT 40 for the forest again shows exceedances of the critical load of 104 ppb.h across all the mapped area of Continental Europe south of 65°N including S.Britian. As land use for forestry and ozone dose both increase with altitude, and these effects have not so far been incorporated in the AOT 40 assessment for forests, the degree of exceedence for forests may have been significantly under-estimated.\u
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