The broad aim of the atmospheric program on an expedition to the central Arctic Ocean during July--September 1996 (AOE-96) was to improve the accuracy of models predicting climatic change by reducing uncertainties associated with the indirect climate effect of aerosols. A major part of this aim was to assess what feedback processes might be involved and their implications for both regional and global radiative forcing. An immediate objective therefore was to study the biogeochemical sources that were thought to lead to aerosol formation and possible growth processes as well as the characterization of the aerosol that actually influences cloud properties in a region where natural processes prevailed. The program was designed as an integrated package to study processes from the sea-ice/air interface to the top of the Arctic boundary layer and involved the contribution from about 25 participating scientists from 8 countries. The results from a previous expedition to the same area were used to specify the research topics from which new or improved information was needed to achieve the objectives. The instruments, techniques, and models developed and deployed to provide the answers are described. The relevant properties of the region, the route of the expedition, the conditions encountered, and the special circumstances of measurements made on an ice floe are also discussed. ¿ 2001 American Geophysical Union