Carbon tetrachloride (CCl4), which was once used in applications such as dry cleaning and as a fire-extinguishing agent, was regulated in 1987 under the Montreal Protocol along with other chlorofluorocarbons that destroy ozone and contribute to the ozone hole over Antarctica. Parties to the Montreal Protocol reported zero new CCl4 emissions between 2007-2012.
However, the new research shows worldwide emissions of CCl4 average 39 kilotons (about 43,000 U.S. tons) per year, approximately 30 percent of peak emissions prior to the international treaty going into effect. "We are not supposed to be seeing this at all," said Qing Liang, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study published online in the Aug. 18 issue of Geophysical Research Letters, a journal of the American Geophysical Union. "It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources."
Note: CCI4s were previously referred to as CFCs, which is to the public the more familiar abbreviation.
That there seems to be an unknown source of CFCs suggests strongly that the entire theory of CFCs destroying the ozone layer is faulty. If CFCs were being produced naturally in the past then the ozone layer should not exist based on this theory. That it does exist says the CFCs are not harmful to it and were banned unnecessarily.