The heterogeneous decomposition of ozone at -50 ¿C, on surfaces coated with 75% sulfuric acid solutions and with 75% sulfuric acid solutions containing a variety of metallic ions and NH4+, has been studied in a static system. The collision efficiency &ggr; (the ratio of the number of reactive collisions to the total number of collisions) for the reaction on each surface has been determined. It was found that the addition of the ions Ni2+, Cu2+, Al3+, Fe3+, and NH4+ did not appreciably modity the reaction rate observed over clean glass or glass coated with the sulfuric acid solution. Mn2+ and Fe2+ did enhance the reaction but only by 2 orders of magnitude for the last ion. However, the largest value of &ggr; observed, 10-9, it still too small to be of any significance in the stratosphere. We conclude that the heterogeneous decomposition of ozone on the stratospheric particle surfaces is of minor importance.