The integrated assessment model, Abatement Strategies Assessment Model (ASAM) is described and applied to the reduction of sulphur dioxide emissions in order to ameliorate European acidification in a cost-effective manner. The use of critical loads to map the spatial variation of environmental sensitivity is a key factor underpinning this approach. Since these critical loads are not in practice attainable, intermediate target loads are required. ASAM is used in this paper to show that the use of the ‘gap-closure’ approach, to define target loads, and in particular the 60% gap-closure target used as a basis for the Oslo protocol, is particularly appropriate. The unique feature of ASAM it its step-wise approach to optimisation which allows examination of an abatement strategy aiming at a particular environmental target at any required overall European expenditure level, even if the target is not attained at this point. This is key to ASAM’s ability to compare the cost-effectiveness of strategies based upon different target-loads. Similarly, ASAM has been used to demonstrate the influence of the use of current reduction plans as a starting point for optimisation in countries which plan substantial emissions reductions. ASAM is also used to show that abatement strategies are robust to large uncertainties in abatement cost estimates in individual countries. Finally, the role played by individual countries in a typical model strategy is investigated by comparing the ecosystem areas brought under protection by expenditure in each country. This work was undertaken in the context of the United Nations Economic Commission for Europe’s (UNECE) preparations for a second sulphur protocol.