Evidence from the ER-2 and DC-8 aircraft flights is considered, together with analyses of temperature, winds, potential vorticity and trajectories, satellite data, and ozonesonde observations, to come to a view of whether the air in the lower stratosphere over Antarctica during winter and early spring of 1987 was a fixed slug of air, or if there was significant mass flow through the system. It is concluded that synoptic-scale forcing, via ''sudden coolings,'' produced polar stratospheric clouds, which intervened to alter the homogeneous gas phase chemical balance. As a result, there was a source of the ClO molecule and sinks for H2O, NOy (equal to the sum of reactive gas phase nitrogen compounds), and O3 operating within the region of high potential vorticity gradients on isentropic surfaces, that is, inside the vortex. It is further concluded that as a result of horizontal mixing, downward diabatic motion, and, at potential temperatures below 400 K, advective transfer, that the effects of these polar sinks and chemical reactions can be transmitted to middle latitudes. ¿ American Geophysical Union 1989