During the preparation of the recent "multi-pollutant, multi-effect" protocol of the Convention on Long-Range Transboundary Air Pollution (LRTAP), just as for that of the European Directive on emission ceilings, discussion of strategies for reducing transboundary air pollution resulting from emissions of sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOC), ammonia (NH3), was focused on a series of highly specific scenarios.