Urban areas are major sources of air pollution. Pollutant emissions affecting air quality in cities are considered to have adverse consequences for human health. Public and government concern about environmental issues arising from urban air pollution has increased over the last decades. The urban air pollution problem is widespread throughout the world and it is important to find ways of eliminating or at least reducing the risks for human health. The fundamentals of the physical and chemical processes occurring during air pollutant transport in the atmosphere are nowadays understood to a large extent. In particular, modelling of such processes has experienced a remarkable growth in the last decades. Monitoring capabilities have also improved markedly in the most urban areas around the world. However, neither modelling nor monitoring can solve urban air pollution problems, as they are only a first step in improving useful information for future regulations. The defining of efficient control strategies can­ not be achieved without a clear knowledge of the complete pollution process, i.e. emission, atmospheric transport and transformation, and deposition at the receptor. Improving our ability to establish valid urban scale source-receptor relation­ ships has been the objective of SA TURN, one of the 14 subprojects of EURO­ TRAC-2. Similar to the other subprojects of this co-ordinated environmental pro­ ject within the EUREKA initiative, SA TURN brought together international groups of scientists to work on problems directly related to atmospheric chemistry and physics. The present volume summarises the scientific results of SATURN.