If you thought that the depletion of the ozone layer was a problems of the '90s, think again: according to new NASA research, the Earth's atmosphere contains an unexpectedly large amount of 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 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?"
That is very good question indeed — and it is, obviously, the next puzzle to solve. [NASA]