Ocurrence of heterogeneous reactions on the surface of Polar Stratospheric Clouds (PSC) is a necessary component of the chlorine-related chemical mechanisms proposed to explain the recently observed decrease of ozone during antarctic spring. A one-dimensional model is used to assess the impact of these heterogeneous reactions on future global ozone trends if they were to occur on the global aerosol layer. The impact of these reactions on the concentration of chlorine species in the present-day atmosphere is also calculated to determine if observations can place any constraints on the rates of these reactions in the global atmosphere. Of the two heterogeneous processes considered here, the reaction (ClNO3+HCl) could have a larger impact on stratospheric ozone. A fast rate for this reaction would greatly enhance the present concentration of ClO and reduce the abundance of HCl in the lower stratosphere. Because of the large differences between the antarctic and global environments, the calculated global O3 trends are smaller than those calculated for Antarctica. In addition to determining kinetic rates in the laboratory, concurrent monitoring of stratospheric concentrations of ClO, HCl, OClO and aerosols at selected locations around the globe during the next 10 to 20 years may provide early clues as to whether such reactions are actually occurring. ¿ American Geophysical Union 1988