Four heterogeneous reactions have been added to a one-dimensional dynamic-chemical model of the stratosphere. The heterogeneous reactions considered were the decomposition of ozone, the recombination of atomic oxygen, the reaction of nitrogen pentoxide with the liquid water dissolved in sulfuric acid particles, and the oxidation of sulfur dioxide by hydrogen peroxide sorbed by the particles. The calculations demonstrate the possibility that each of these reactions with the probable exception of heterogeneous atomic oxygen recombination plays an important role in stratospheric chemistry. The results emphasize the need for experimental determinations at stratospheric temperatures of the fraction of collisions between reactive atoms or molecules and impure sulfuric acid particles that result in chemical reactions.