The two-dimensional model of stratospheric constituents is presented in detail. The derivation of pertinent transport parameters and the numerical solution of the species continuity equations, including a technique for treating the stiff differential equations that represent the chemical kinetic terms, and appropriate methods for simulating the diurnal variations of the solar zenith angle and species concentrations are discussed. Predicted distributions of tracer constituents (ozone, carbon 14, nitric acid) are compared with observed distributions. Whitten, R. C. and Borucki, W. J. and Watson, V. R. and Shimazaki, T. and Woodward, H. T. and Riegel, C. A. and Capone, L. A. and Becker, T. Ames Research Center NASA-TP-1003, A-6982 RTOP 197-30-02