This is a project to identify and quantify atmospheric ions naturally occurring in the troposphere. It employs a tandem mass spectrometer in conjunction with a specially developed collisional dissociation chamber that strips loosely bound ligand molecules from the central core ion, thus allowing mass spectrometric observation of the core ion itself. The operation of the apparatus depends on the development, in an earlier stage of the research, of a gas.flow system for extracting the ions from air at atmospheric pressure and injecting them into the vacuum system of the mass spectrometer. The objective is to survey the natural existence in the lower atmosphere of molecular ions and ionized molecular clusters. The chemical nature of the ions is to be determined, as well as their origins, their abundance under a range of environmental conditions, and their roles as indicators of trace gases. Ultimately the work is expected to identify the possible roles of ions in aerosol formation and growth.