If you thought that the depletion of the ozone layer was a problem confined to the '90s, think again: according to new NASA research, the Earth's atmosphere contains an unexpectedly large amount of an ozone-depleting chemical, decades after it was banned worldwide.
The new study shows that carbon tetrachloride — once used in dry cleaning and fire extinguishers but banned along with other chlorofluorocarbons (CFCs) back in 1987 — is still emitted at a rate of 39 kilotons per year. That's down 30 per cent from its peak output, but way, way higher than it should be; in theory, emissions of the compound should be practically zero by this point.
Parties to the Montreal Protocol (the agreement that banned the use of chlorofluorocarbons) reported zero new CCl4 emissions between 2007-2012. That means the compound's presence, which should have declined at a rate of 4 per cent per year, has in fact been decreasing at less than 1 per cent — so there must be some other source for the compound. Qing Liang, an atmospheric scientist at NASA's Goddard Space Flight Center, explains:
"We are not supposed to be seeing this at all. It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources. Is there a physical CCl4 loss process we don't understand, or are there emission sources that go unreported or are not identified?"