This is a myth, arising from a misinterpretation of an out-of- context quotation from a review article by Dobson.

In his historical account [Dobson 1968b], Dobson mentioned that when springtime ozone levels over Halley Bay were first measured, he was surprised to find that they were about 150 DU below corresponding levels (displaced by six months) in the Arctic. Springtime arctic ozone levels are very high, ~450 DU; in the Antarctic spring, however, Dobson's coworkers found ~320 DU, close to winter levels. This was the first observation of the normal, pre1980 behavior of the Antarctic ozone layer: because of the tight polar vortex (see below) ozone levels remain low until late spring. In the Antarctic ozone hole, on the other hand, ozone levels decrease from these already low values. What Dobson describes is essentially the baseline from which the ozone hole is measured.