Scientists have discovered a rise in emissions of an ozone-depleting chemical whose levels are supposed to be “at or near zero,” suggesting someone is violating the 1987 Montreal Protocol, according to The Washington Post. CFC-11, used to make foam, climbed “25 percent since 2012,” despite being one of the chemicals that were supposed to be “phased out” under the environmental accord. The chemical can reportedly stay in the atmosphere for over 50 years once released, and damage the ozone layer. Researchers have surmised that the polluter may be emitting the illegal chemical somewhere in East Asia, but can’t narrow it down any further than that. While it’s likely that the producer is “cheating,” researchers also haven’t ruled out more innocent causes—like “accidental” production and the release of CFC-11 via demolished buildings.