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Invited contribution to subproject TOR-2

There is mounting evidence that the emissions of NOK and VOC in various countries in Europe are decreasing. According to the EMEP Emission Inventory NOK, NMVOC and CO emissions decreased from 1988 to 1995 with about 10-30 % in many countries in NW Europe (EMEP, 1996).
Records of ambient air measurements seem to confirm the downward trends of these species in this part of Europe. Substantial (2-3 <>/o/yr) downward trends of NO2 concentrations over the last 5-8 years are seen at sites in Germany (Deuselbach, Waldhof), Sweden (20-30 sites in the Swedish network), The Netherlands, Belgium and The United Kingdom (Svanberg and Lindskog, 1996; de Paus and Roemer, 1997; AEA, 1995). From data at Moerdijk, a site in the Netherlands it is clear that traffic related VOC have decreased with 40-50 % over the last 10-15 years. Measurements at Mace Head, Ireland show for the 1990-1994 period a decrease of about 7 %/yr of CO concentrations in air coming from Europe (Simmonds et al., 1996).
It is therefore interesting to see if an effect of the emission reductions is visible in the ozone data. Model calculations (EMEP, LOTOS, EURAD and other models) suggest a rather small response in the ozone concentrations, and perhaps even a small increase of ozone concentrations in the NOK rich areas of the Low Countries, Germany and the United Kingdom.
If evaluation of the data (emissions, precursor and ozone concentrations, meteorological data) results in establishing a relation between the response of ozone concentrations to emission reductions it allows to develop more efficient abatement strategies in the future.