Final answer:
The South polar ozone hole forms in the Southern Hemisphere's spring due to the presence of PSCs that trap compounds that deplete ozone, combined with the isolation caused by the polar vortex and increased sunlight.
Step-by-step explanation:
The South polar ozone hole forms during August through November because of a combination of extreme cold temperatures and the presence of polar stratospheric clouds (PSCs) that trap chlorine and nitric acid. When sunlight returns in the spring, it speeds up the chemical reactions involving these trapped compounds and depletes ozone molecules, a process exacerbated by the polar vortex that isolates these reactions over the Antarctic region. This period coincides with springtime (September to early December in the Southern Hemisphere), which is when the ozone hole is observed to increase significantly in size.