Setting international targets for controlling atmospheric emissions of pollutants — now and in the future

Current discussions on controlling emissions of atmospheric nitrogen pollutants in Europe are adopting a multi-pollutant, multieffect strategy where acidification, eutrophication and the effects of photochemical oxidants are all taken into account. Parallel activities by both the Convention on Long Range Transboundary Air Pollution (ratified by 42 governments of the 55 countries in the UNECE area) and the EU are making use of the critical loads approach and integrated assessment models to arrive at cost optimized scenarios for environmental protection. Critical loads and critical levels are used to define the thresholds for effects; as these are usually difficult to attain they are being used to set.intermediate target objectives. A number of different methods for setting such targets, the so-called “gap closures” are being investigated. While the basis for estimating critical loads and levels has been extensively researched, collection of the necessary data and the development of methods continue to evolve. Current discussions on international agreements for emission reductions are based upon the best available information, but this has limitations which are often difficult to build into the decision making process. It is to be expected that any currently derived results will be an interim and very approximate solution for the problems resulting from pollutant emissions. Further steps will require better information on impacts and probably alternative approaches to the critical loads concept as it currently stands.