A two-dimensional atmospheric transport simulation model is described which is designed to facilitate the interpretation of observed distributions of primary tropospheric trace gases. Transport by large scale advection is based on published meridional velocisty fields, while the eddy diffusion component of the transport is based on published diffusion coefficients adjusted to produce agreement between model generated and observed global distributions of CCl3F. The observed CCl3F distribution presented here is useful in this context as it is based on recent multiple observations at six globally distributed background monitoring stations which use calibration gases based on a common standard. The model incorporates both northern and southern hemisphere CCl3F release estimates. It is found that in recent years the global rate of increase in tropospheric CCl3F concentration is higher than that consistent with available release data. The model results indicate interhemispheric exchange time (70¿N to 70¿S) of approximately 8 months.