Ozone-Depleting Compound is Being Released into Earth's Atmosphere Despite Montreal Protocol

It turns out that our ozone is still in danger. Scientists have examined Earth's atmosphere and have found an unexpectedly large amount of an ozone-depleting compound from an unknown source even though it's been decades since the compound has been banned worldwide.

The compound in question is carbon tetrachloride (CCl4), which was once used in everything from dry cleaning to a fire-extinguishing agent. In 1987, this compound was regulated under the Montreal Protocol along with other chlorofluorocarbons that had the potential to destroy the ozone and contribute to the ozone hole over Antarctica.

Even with this agreement, though, it seems like there are still emissions of CCl4 occurring. In fact, scientists have found that there's an estimated 39 kilotons per year being emitted into the Earth's atmosphere; that's about 30 percent of peak emissions before the treaty went into effect.

"We are not supposed to be seeing this at all," said Qing Liang, lead author of the new study, in a news release. "It is now apparent there are either unidentified industrial leakages, large emissions from contaminated sites, or unknown CCl4 sources."

For years, researchers have wondered why the levels of CCl4 in the atmosphere have declined slower than expected. Now, it seems as if they may have an answer. With zero CCl4 emissions between 2007 and 2012, atmospheric concentrations of the compound should have declined at about four percent per year. Yet it seems that that rate is only about one percent per year.

The researchers used NASA's 3D GEOS Chemistry Climate Model and data from global networks of ground-based observations. In the end, they found that there had to be an unidentified, ongoing current source of CCl4 in order to explain the discrepancy.

"People believe the emissions of ozone-depleting substances have stopped because of the Montreal Protocol," said Paul Newman, co-author of the study. "Unfortunately, there is still a major source of CCl4 out in the world."

The findings are published in the journal Geophysical Research Letters.