Finnish–Estonian air ion and aerosol workshops

Atmospheric air ions and aerosol particles participate in atmospheric processes and have several important effects on e.g. global climate and human health. When measured, air ions and aerosol particles have been observed to be present always and in every place. In this overview we present a brief summary of the motivation, history and main achievements in air ion research. The papers in this special issue are the result of a set of bi-annual workshops taken place since 2003. The contents of the papers reflect the collaborative research efforts lead by the University of Helsinki and University of Tartu, with an increasing contribution of other partners. The main objective of these workshops has been to provide a discussion forum for the development of air-ion theory and measurement techniques. This special issue presents main achievements in a set of 14 original papers.