Tackling multi-pollutant multi-effect problems } an iterative approach

Within both the UN ECE and the European Union, there has been a strong move towards the so-called multi-pollutant multi-effect approach to air pollution strategies. In this approach a number of pollutants are considered, and emission reductions are determined after looking at the effect of each of these pollutants on a number of environmental problems. This new approach is very ambitious and raises a number of problems in balancing the effects and costs of different emission reductions against achieved environmental benefits. We describe an iterative method designed for addressing such multi-pollutant multi-effect type problems. In the examples given here, the method is used to estimate combinations of NOx and VOC emission reductions from all European countries so as to reduce environmental problems associated with acidification and ozone in a cost-effective manner. The iterative technique is designed to be flexible and transparent, so that a number of different approaches to multi-pollutant-multi-effect problems can be considered. This technique can be used to provide early guidance on various control strategy options, and allows rapid exploration of the many targets and measures possible with these approaches. It also demonstrates how even complex multi-dimensional environmental problems may be amenable to understandable solutions.