That 40 - 50 km altitude absorption is where the high energy UV - c is absorbed. (theinconvenientskeptic.com)
The graph below from the International Panel on Climate Change (IPCC) Fourth Assessment Report (4AR) shows the predicted tropical troposphere hot - spot at 8 to 12 km altitude as a distinctive red area. (friendsofscience.org)
Professor Chipperfield said: «Ozone depletion in the polar regions depends on meteorology, especially the occurrence of cold temperatures at about 20 km altitude — colder temperatures cause more loss. (sciencedaily.com)