The sudden onset of ozone depletion in the Antarctic vortex set a precedent for both the time scale and the severity of global change. The AIRBORNE ANTARCTIC OZONE EXPERIMENT (AAOE) staged from Punta Arenas, Chile, in 1987, established that CFCs and Halons are the source of chlorine and bromine radicals that, in turn, control the rate of ozone destruction, that the vortex is depleted in nitrogen oxides, reactive nitrogen, and water vapor and that diabatic cooling during the antarctic winter leads to subsidence within the vortex core importing air from higher altitudes and lower latitudes. This last conclusion is based on observed dramatic distortion in the tracer fields, most notably N2O.
In 1989 the AIRBORNE ARCTIC STRATOSPHERIC EXPEDITION (AASE) staged from Stavanger, Norway, using the same aircraft employed for AAOE, the NASA ER-2 and the NASA DC-8, discovered that while NOx and to some degree NOy were perturbed within the arctic vortex, there was little evidence for desiccation. Under these (in contrast, to the antarctic) marginally perturbed conditions, however, ClO was found to be dramatically perturbed such that a large fraction of the available (inorganic) chlorine resided in free radical and free radical dimer form.

This leaves two abiding issues for the northern hemisphere:

1. Will significant ozone erosion occur within the arctic vortex in the next ten years as chlorine loading in the stratosphere approaches 5 ppbv? that is, will an "ozone hole" appear in the northern hemisphere by decade's end?

2. Which mechanisms are responsible for the observed ozone erosion poleward of 30 degrees n in the winter/spring northern hemisphere reported in satellite observations?