“Ozone depletion is a well-known phenomenon and, thanks to the success of the Montreal Protocol, is widely perceived as a problem solved,” says University of East Anglia’s David Oram. But an international team of researchers, led by Oram, has now found an unexpected, growing danger to the ozone layer from substances not regulated by the treaty. The study is published today in Atmospheric Chemistry and Physics, a journal of the European Geosciences Union.