Last year, a report surfaced that suggested someone, somewhere was producing a huge amount of an ozone-destroying chemical which had already been banned worldwide way back in 2010. Scientists knew it was being pumped into the air, but they didn’t know where it was coming from or who was doing it. Now, scientists report that they’re getting much closer to finding the culprit.

A new report published in Nature has traced the source of the ozone-eating trichlorofluoromethane (CFC-11) to eastern China. Using global monitoring information and data from locations around eastern Asia, researchers have narrowed down the region where the CFC-11 is being produced, but some questions still remain.

After crunching the numbers from various locations the researchers detected a dramatic increase in CFC-11 emissions in the areas of Shandong and Hebei in northeastern China. The sheer amount of the chemical coming from these regions accounts for up to 60 percent of the global spike in CFC-11 reported last year. However, the scientists can’t venture a guess as to the exact source just yet.

“A recently reported slowdown in the decline of the atmospheric concentration of CFC-11 after 2012, however, suggests that global emissions have increased,” the study explains. “A concurrent increase in CFC-11 emissions from eastern Asia contributes to the global emission increase, but the location and magnitude of this regional source are unknown.”

The study reveals that no other elevated levels of CFC-11 appear to be coming from any other eastern Asian countries and that these specific areas of China are likely responsible for the majority of current CFC-11 emissions worldwide. That said, not all of the CFC-11 in the atmosphere is being emitted from China, meaning that there are other factors at play and likely other countries who are either willfully or unwittingly ignoring agreements made to halt production of the chemical nearly a decade ago.