Simultaneous Optimization of Abatement Strategies for Ground-Level Ozone and Acidification

An updated Protocol on emissions of nitrogen oxides, under the UN/ECE Convention on Long-range Transboundary Air Pollution, is now at a preparatory stage. An effect-based approach is to be applied to the environmental problems to which nitrogen oxides contribute, either singly or in combination with other pollutants. One such multi-pollutant problem is ground-level ozone. In order to assist the negotiations on the forthcoming NOx Protocol, IIASA has developed an integrated assessment tool that can be used to support the development of cost-effective European emission control strategies targeted at ground-level ozone. This report present a number of scenarios to illustrate the main features of ozone-related emission control strategies. One crucial element is the selection of appropriate environmental targets. Some alternative approaches are described to illustrate the problems involved and the implications of particular solutions. The target-setting process is, however, a genuinely political task, requiring judgments about political priorities. The AOT60 has been use here as a health-related indicator of ozone exposure. Special attention is devoted to the considerable inter-annual variability in ozone due to differences in meteorological conditions. A possible approach for dealing with the problems caused by this variability is presented. An illustrative control strategy for the reduction of vegetation damage by ozone is described, using the AOT40 exposure measure. For some areas of high NOx emission density in NW Europe, the currently planned emission reductions would lead to an increase in the AOT40, owing to the non-linear character of ozone formation. However, it is possible to reduce ozone-related vegetation damage throughout Europe by reducing NOx emissions beyond the current plans. Recent progress has been made in considering different environmental targets together. This is illustrated by an optimization scenario which deals simultaneously with health- and vegetation-related ozone strategies. Such an approach offers a certain potential for cost savings. Finally, the report illustrates the interaction of ozone control strategies with acidification, using an optimized emission control scenario aimed at the simultaneous achievement of environmental targets for AOT60, AOT40 and acidification.