00:38 Levels of Ozone-eating Chemicals on the Rise Scientists are concerned over rising levels of ozone-eating chlorofluorocarbons in the atmosphere.

At a Glance Since 2013 more of the banned CFC-11 has gone into the atmosphere, scientists say.

Monitoring stations suggest the emissions are coming from northern Asia, specifically China, Mongolia and the Korean peninsula.

An ozone-eating chemical that has been banned for years is mysteriously on the rise again in the atmosphere, scientists say.

In 1987, countries around the world agreed to phase out chlorofluorocarbons (CFCs) under the Montreal Protocol after scientists concluded that the chemicals were depleting the protective ozone layer of the atmosphere.

The ban worked and the size of the developing hole over the South Pole began to shrink.

But, according to a study published Wednesday in the journal Nature, there has been a 25 percent increase of emissions of one of the chemicals , trichlorofluoromethane or CFC-11, since 2013. The chemical is the second-most common CFC in the atmosphere and has been used to make foam, degrease stains and for refrigeration, the Associated Press notes.

“It’s the most surprising and unexpected observation I’ve made in my 27 years” of measurements," study lead author Stephen Montzka, a research chemist at the National Oceanic and Atmospheric Administration, told the AP. “Emissions today are about the same as it was nearly 20 years ago."

While countries have reported nearly zero emissions of the chemical since 2006, the researchers found that roughly 14,300 tons a year of CFC-11 has been released since 2013.

Montzka said his team from NOAA's Cooperative Institute for Research in Environmental Sciences, the United Kingdom and the Netherlands became "detectives of the atmosphere" to try to determine the cause of the increased levels of CFC-11.

Monitoring stations suggest the emissions are coming from northern Asia, specifically China, Mongolia and the Korean peninsula, the study notes.

The researchers say the chemical can be a byproduct of other chemical manufacturing, although it's supposed to be captured and recycled.

(MORE: America's Success Story In Saving Ozone Layer Has Added Climate Benefits, Study Says )

Montzka said the most likely scenario is someone is producing new CFC-11.

"In the end, we concluded that it’s most likely that someone may be producing the CFC-11 that’s escaping to the atmosphere ," he said in a press release. "We don't know why they might be doing that and if it is being made for some specific purpose, or inadvertently as a side product of some other chemical process."

While concentrations of CFC-11 in the atmosphere continue to decline, they’re declining more slowly than they would if there were no new sources.

Montzka noted that if the source of these new emissions can be identified and controlled soon, the damage to the ozone layer should be minor. If not remedied soon, on the other hand, substantial delays in ozone layer recovery should be expected.

"We're raising a flag to the global community to say, 'This is what's going on, and it is taking us away from timely recovery from ozone depletion,'" Montzka said in a press release. "Further work is needed to figure out exactly why emissions of CFC-11 are increasing and if something can be done about it soon."