This paper gives an overview of (1) how sulfur and nitrogen oxide emissions are calculated in ENEM, (2) how the RAINS user can create emission forecasts and reduction scenarios, (3) how associated emission control costs are computed, and (4) how cost-optimal solutions can be found for given environmental targets. To illustrate these points, we implemented several realistic control scenarios for sulfur and nitrogen. For NO2, we only show resulting country-specific emission levels and total reduction costs, whereas for SO2, we show in addition the corresponding deposition patterns over Europe. Results make it clear that, compared with 1985 emissin levels, countries could substantially reduce their emissions further until the year 2000. With the currently best available technology, both sulfur and nitrogen oxides could be reduced by 60 percent. These reductions would come at a substantial annual cost of between 66.5 billion DM for nitrogen and 95.3 billion DM for sulfur, but would achieve deposition levels close to currently accepted critical loads. On the other hand, commitments made to- date by various European countries are insufficient to achieve acceptable environmental deposition levels. In order to find practicable intermediate solution in which any additional, overall European funds are spent most effectively, RAINS can be applied in its optimization mode. These results show that, for sulfur, those countries with the highest emissions, as well as deposition levels, could most cost-effectively reduce their emissions and would simultaneously achieve the greatest environmental benefit for all Europe. Such RAINS results could be used in bilateral discussions to explore the possibilities of neighbouring countries transfering funds to the other country because actual reduction costs would be lower than at home, but at the same time, the environmental benefits at home would still be larger from these reductions than from further reducing emissions domestically. RAINS is thus a good tool to investigate the potential of where funds are best applied to emission reductions for getting the biggest environmental benefit.
