A two-dimensional zonally averaged transport model of the atmosphere up to 10 mbar (~33 km) has been developed. The transport is described by an effective stream function and a diffusion tensor derived from a three-dimensional general circulation model. The numerical solution of the transport equations has been given special attention, and a positive definite mass conservative advection scheme which produces small numerical diffusion has been modified for use in the model. In addition to the vertical transport described by the transport equations, a parametrization of the vertical mixing due to convective clouds and frontal circulation is included in the model. The model has been tested with different tracers which indicated a realistic representation of the atmospheric transport. ¿ American Geophysical Union 1993