The ozone-oxygen cycle that keeps the ozone layer relatively stable has been derailed. The problem is that more ozone is breaking down than the sun can rebuild. This imbalance comes from the "hole," or thinning, in the ozone layer over Antarctica. Human-produced ozone-depleting compounds are doing most of the damage.
Ozone-depleting compounds contain bromine, chlorine, fluorine, carbon and/or hydrogen in different combinations. You've probably heard about one of the most common types of ozone-depleting compounds, known as chlorofluorocarbons (CFCs). CFCs contain only fluorine, carbon and chlorine, and traditionally have been used in refrigeration, air conditioning, aerosol cans and as industrial solvents. An over-abundance of these compounds, released into the air by human activities, has resulted in the Antarctic ozone hole.
Complex chemical reactions, which occur in Antarctica during the winter and spring, act to destroy ozone. In the winter, the sun doesn't reach the South Pole and a polar vortex forms. The polar vortex is an air current around the pole that isolates the air. The CFCs that arrive at the vortex can't get out, so they become concentrated there.
When sunlight returns to Antarctica in the spring, chemical reactions on the surface of these clouds break ozone-depleting compounds down into atoms of chlorine and bromine. These atoms are deadly to ozone. One chlorine atom can break apart 100,000 ozone molecules, and bromine is 40 times more destructive [source: EPA]. This happens naturally in the stratosphere, but the chlorine and bromine there isn't as concentrated as it becomes during the Antarctic spring. These atoms destroy much of the ozone over Antarctica, throwing off the balance of the rest of the ozone layer.
The polar vortex exists only over Antarctica, which is why the ozone "hole" exists only there. But the bigger the hole gets, the thinner the ozone layer will become over the rest of the Earth. This means more dangerous UV radiation will reach the Earth's surface.
An obvious solution, then, would be to pump more ozone up there to try to counteract the thinning. But creating an ozone patch is not a simple proposition.