Our planetary system naturally restores ozone in the stratosphere. The earth was hit by a solar storm on October 28, 2003 that destroyed around 75% of the ozone in Earth's middle atmosphere.
http://www.agu.org/pubs/crossref/200...GL021521.shtml
As a result the ozone hole was largest in 2003 at around 29 million kilometers.
The damage from this storm caused the United Nations weather organization to add 15 years to the ozone hole recovery rate, moving the recovery period out to 2065.
http://www.agu.org/pubs/crossref/200...GL021521.shtml