This special Issue of Water, Air, and Soil Pollution: Focus provides original con­ tributions from The Sixth International Conference on Air-Surface Exchange of Gases and Particles, held in Edinburgh between 3 and 7 July 2000. The first 5 conferences in this series, all in the U. S. A. , focussed on the underlying processes of removal of trace gases and aerosols from the atmosphere, including many of the major air pollutants. In maintaining this focus from the outset in 1970 the conference series has described the development of understanding of major parts of the Acid Deposition story, and the processes of removal of radioactive aer­ osols and gases from the atmosphere. More recently, the range of compounds included in surface-atmosphere exchange research has expanded as the role of deposition and emission has been recognized as a key component of a much larger range of environmental issues. It is timely that the venue of the meeting has also moved, reflecting the increasingly international collaboration developed to study environmental problems that are, for the most part trans-boundary issues. It is 10 years since the last conference in this series, in Richland Washington, U. S. A. and the subject has developed considerably in the decade, both in the cur­ rent focus, which has moved away from sulphur compounds and towards nitrogen, and in the application of new methods and models.