Emission of pollutants, followed by their atmospheric transport and deposition, is one of the various routes which lead to exposure of man and the environment. Ambient concentration levels and deposition loads can be predicted by the use of atmospheric transport models. However, such models require knowledge of the physical and chemical properties of the emitted compounds. The aim of this study was to describe procedures which estimate these properties for organic compounds. The discussion of the procedures is structured according to the input requirements of the OPS model. This model, developed by RIVM, predicts the atmospheric behaviour of substances on the basis of a few compound- specific parameters. These parameters can be derived from the vapour pressure, the Henry coefficient and the reactivity of the substance. This report indicates the data bases and literature sources which present relevant information on organic compounds. Furthermore, for those cases where the necessary information is not available, calculation methods are indicated which may support the derivation of compound-specific parameters. The project cluster "Evaluation System for New Substances" (BNS) aims to develop systematic methods to support risk assessment of the production and use of new chemicals. The OPS model, combined with the procedures outlined in this report, may be one of the tools to assess the risks which are related to atmospheric transport of pollutants.