Ozone measurements in Europe

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

Trends of ozone in the troposphere

Using a set of selected surface ozone (nine stations) and ozone vertical profile measurements (from six stations), we have documented changes in tropospheric ozone at a number of locations. From two stations at high northern hemisphere (NH) latitudes there has been a significant decline in ozone amounts throughout the troposphere since the early 1980s. At midlatitudes of the NH where data are the most abundant, on the other hand, important regional differences prevail. The two stations in the eastern United States show that changes in ozone concentrations since the early 1970s have been relatively small. At the two sites in Europe, however, ozone amounts increased rapidly into the mid1980s, but have increased less rapidly (or in some places not at all) since then. Increases at the Japanese ozonesonde station have been largest in the lower troposphere, but have slowed in the recent decade. The tropics are sparsely sampled but do not show significant changes. Small increases are suggeste d at southern hemisphere (SH) midlatitudes by the two surface data records. In Antarctica large declines in the ozone concentration are noted in the South Pole data, and like those at high latitudes of the NH, seem to parallel the large decreases in the stratosphere