This project is investigating the thermodynamic properties associated with the growth of small aerosols (approximately 3-50 nm) in the laboratory as a function of composition, temperature and size. At present, very little is known about very small particles that serve as the critical nuclei for nucleation and input for models of aerosol formation and growth in the atmosphere and large discrepancies exist between model predictions and field observations. This work is expected to lead to a greater understanding of the Kelvin effect (particle surface-tension effect) on particle phase transitions and the new particle formation of pure aerosols. During the final phase of the study, size-selected field samples will be collected and analyzed for comparison with the laboratory results.