Arctic ozone was severely depleted in the winter of 1999/2000 due to reactions on polar stratospheric clouds, leading to a 70% reduction in ozone levels in the lower stratosphere. Different instruments confirmed this loss, totaling 117 ± 14 Dobson units by winter's end. Despite this chemical loss, ozone levels remained relatively constant throughout the winter due to a balance between chemical depletion and ozone redistribution. This contrasts with the usual increase in ozone levels observed in most years during the same period.