As the regional models required to understand and control the generation, distribution and deposition of air pollutants become more precise, the need to understand the detailed effects of hilly and mountainous terrain becomes more acute. The Alpine regions and the mountainous Mediterranean coasts have large effets on the way the pollutant burden is spread in their areas. Similarly an understanding of the effects of chemical and physical processes controlling pollutant deposition and the emission of biogenic compounds is essential to the correct modelling of the coastal regions which surround so much of Europe. The results from two projects on these problems are presented in this volume: one involved a series of field campaigns in the Alps and in the Rhine valley, the other involves ships and platforms in the North Sea and also in the Mediterranean.