Hong Kong (CNN) A mystery source of banned, ozone-destroying chemicals has been pinpointed to eastern China.

Scientists noted a spike in the amount of chlorofluorocarbons , or CFCs, in the atmosphere last year, despite a global ban on their use. The source of the emissions remained unknown, however, sparking concerns that it could hamper years of international effort to repair the protective ozone layer.

CFCs used to be common in refrigerators, aerosol cans and dry cleaning chemicals. But they were banned under the Montreal Protocol of 1987, after it was discovered they contributed to the creation of a giant hole in the ozone layer that forms over Antarctica each September. A global phaseout of CFCs has been in place since 2010.

The ozone layer, a fragile shield of gas, protects animal and plant life on Earth from powerful UV rays. When the ozone layer is weakened, more UV rays can get through and affect humans, making them prone to skin cancer, cataracts and other diseases. There also may be consequences for plant life, including lower crop yields and disruptions in the ocean's food chain.

After concerted global action, the hole in the ozone layer was gradually beginning to mend, but last year, scientists at the US National Oceanic and Atmospheric Administration discovered a sharp rise in CFCs from an unknown source.

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