The development of European policies on air pollution prevention is currently in an intensive phase. The European Commission Clean Air for Europe (CAFE) programme is preparing an air pollution strategy and the Convention on Long-range Air Pollution may start a review of the Gothenburg Protocol during 2005. On the 25th-27th of October 2004 a workshop on review and assessment of the scientific basis and tools employed in this policy work was held to provide guidance to the policy development. Future needs of scientific support in a longer perspective were also discussed. A large part of the workshop was focussed on the role of airborne particles. Human health effects caused by exposure to airborne particles have received increasing attention in recent years and concerns of health effects are today the main driving force for air pollution prevention and research. In addition to this, new concepts for describing effects of acidification and ozone are being introduced, providing more accurate and relevant descriptions of ecosystem effects to changes in air pollution levels. The needs for considering air pollution on a hemispheric scale were also highlighted. This workshop was organised by the ASTA programme, the Swedish research programme on air pollution, in co-operation with the Nordic Council of Ministers, the EU CAFE programme and CLRTAP.