A one-dimensional diffusion model was combined with literature values for the rates of gas phase SO2 oxidation reactions to calculate the stratospheric SO4-- profile. The results showed that the reactions of such trace species as OH and HOO with SO2 are sufficiently fast to produce a sulfate layer above the tropopause similar to the observed Junge layer; the sensitivity of the model to the selection of boundary conditions and eddy diffusion profiles was also investigated.