The model portion of the program has resulted in one- and two-dimensional time-dependent models, which have been used to investigate the distribution of various trace constituents and to study dynamical and radiative processes in the stratosphere. A three-dimensional spectral model that includes the interactions of dynamics and radiation is currently being combined with an aerosol transport model to assess aerosol climatic effects. Because the radiative scattering properties of stratospheric aerosols are very important to climatic conditions on the Earth, studies are being carried out to quantitatively evaluate such properties. This investigation has resulted in measurement of the optical properties of volcanic rocks and ash and sulphuric acid toward the development of an appropriate radiative transfer model and to an application of the model to climatic effects of aerosols from volcanic eruptions, and development of predictive one- and two-dimensional models of the stratospheric sulfate layer.