During the AASE Campaign in 1989, scientists found high levels of chlorine compounds in the Arctic stratosphere. This, combined with polar stratospheric clouds, led to a 17% decrease in ozone levels on two flights. Models suggest that ozone depletion peaked in late March 1989, with a 5-8% decrease at 70° N. Ground-based measurements, however, showed temporary ozone variations and a significant increase, likely due to stratospheric warming. The impact of chlorine on ozone levels was not clearly seen due to these variations.