It's been decades since the world realized the danger that chlorofluorocarbons (CFCs, formerly found in products like aerosol sprays, refrigerants, and solvents) posed to the Earth's ozone layer. But despite the fact that the CFC known as carbon tetrachloride (CCl4) was banned way back in 1987, a new study from NASA shows a troubling amount of the compound in our atmosphere — something that presents a continued threat to the hole in the ozone layer over Antarctica.
"We are not supposed to be seeing this at all," said NASA's Qing Liang, lead author of the study. "It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources." Between 2007 and 2012, studies showed now new CCl4 emissions — but this new study shows that worldwide emissions of CCl4 were still at 30 percent of their peak levels back before ban went into effect. The study also showed that concentrations of the compound were declining by only one percent per year during that 2007 to 2012 time period, not by the four percent rate originally estimated.
Beyond the unexplained sources of CCl4, the compound is also staying in the atmosphere 40 percent longer than earlier studies showed. "Is there a physical CCl4 loss process we don't understand, or are there emission sources that go unreported or are not identified?" Liang asked. But unfortunately, the team behind the study isn't ready to release any theories about what's causing the higher-than-expected concentration of ozone-depleting chemicals.