Scientists have spotted four mysterious ozone-depleting gases in Earth's atmosphere, two of which are still accumulating and causing researchers some concern, AFP reports. Three of them are chlorofluorocarbons—which were mostly banned by the 1987 Montreal Protocol—and one is another ozone-destroying gas called a hydrochlorofluorocarbon. The scientific team from Europe and Australia says the gases are likely coming from the northern hemisphere, possibly due to chemicals used in electronic-component cleaning or insecticide production.
Most concerning of the four is CFC-113a, which is being emitted in small amounts but still doubled between 2010 and mid-2012, New Scientist reports. This particular chlorofluorocarbon was covered in a loophole that let industries apply for exemptions to the Montreal Protocol, said lead researcher Johannes Laube. "What's more, the three CFCs are being destroyed very slowly in the atmosphere—so even if emissions were to stop immediately, they will still be around for many decades to come," said Laube, the BBC reports. (Read more ozone layer stories.)