Optimized acid rain abatement strategies using ecological goals

This article addresses the use of critical loads in optimized emission abatement strategies. Critical loads represent the maximum tolerable deposition possible without adverse impacts, a limit that is highly spatially variable. As deposition targets, critical loads cannot be satisfied at all receptors in Europe. Consequently, there is a need for alternative criteria that still relate to ecological indicators, yet that are feasible, consistent, and equitable. Two criteria are suggested: the relative critical load coverage and the relative deposition reduction. Deposition goals based on these criteria will guarantee that a specified fraction of ecosystems will attain target loads and thus will be protected from adverse environmental impacts. In areas that cannot achieve target loads with the best available control measures, deposition can be reduced to a specified fraction of the unabated level. Examples are presented that demonstrate their derivation and application of the two criteria. The criteria have been implemented in the European-scale Regional Acidification Information and Simulation (RAINS) model. Results obtained indicate that optimized emission strategies based on critical loads may be similar to emission strategies based on deposition reductions at certain levels of the two criteria. This suggests that it may not be necessary to utilize critical loads to formulate deposition targets. A second example shows the effect of excluding countries from European cost minimization. A country's participation can save costs with moderate deposition targets; however, significant costs can be imposed with low (stringent) deposition targets. These preliminary results have significant implications for multilateral negotiations.