In their recent ACPD article, A.Y. Park and co-authors take a statistical look at Umkehr ozone profiles at Boulder, USA, and Arosa, Switzerland. Using principal component analysis and a number basis functions they found that they could accurately capture fine variations in the time evolutions of ozone profiles. At Boulder, strongly declining trends from 2003-2011 at altitudes of 64-32hPa were found, indicating that stratospheric ozone over this region is not yet fully recovering. Find the full abstract here.