Within the framework of the UN-ECE convention for long-range transport of air pollution critical levels of ozone of forests and crops have been determined.
In this report procedures to construct maps of the Netherlands showing actual ozone concentrations for comparison with the critical levels, are presented. The critical ozone levels both for forests and for agricultural crops are frequently exceeded in the Netherlands. The extend of exceedances depend on the meteorological conditions ; a hot, sunny summer like 1989 or 1990 results in exceedances with a factor 2 or 3 in the whole of the Netherlands. In a cold, rainy summer like 1991 or 1993 minor exceedances are observed in some parts (mainly in the south) of the country.