Scientists have discovered four new ozone-depleting gases in the atmosphere, which had previously not been identified.
The scientists, led by Dr Johannes Laube from the University of East Anglia, found three new chlorofluorocarbons (CFCs) and one new hydrochloroflurocarbon (HCFC), according to an article this week in the journal Nature Geoscience.
"There have been seven CFCs and six HCFCs known to be present in the atmosphere and contributing to ozone destruction, and now we've found four more," Laube said.
The gases, which may have been used in making pesticides or refrigerants, have previously gone unnoticed as they were at very low levels and tricky to detect.
Armed with new measurement techniques, Laube and colleagues examined air bubbles trapped deep within firn snow in Greenland and an archive of air samples collected at Cape Grim in Tasmania which dates back to 1978.
They estimate that more than 74,000 tonnes of the gases had been emitted before 2012.
While, this is small compared to the millions of tonnes of CFCs produced every year in the 1980s, Laube said two of the gases show very concerning trends.
"Two of the CFCs do what you would expect for CFCs — they increase in the 1980s, they slow down their increase in the 1990s, and then slowly start to decline. But the other two gases, they don't do that," he said.
"The other two gases are actually becoming more abundant and this indicates that they are still being emitted into the atmosphere."
CFC production was phased out under the Montreal Protocol, and a complete ban on CFC production came into effect in 2010. These actions have led to a gradual decrease in atmospheric CFC levels, and the hole in the ozone layer has also shown signs of recovery.
But Laube warned continued emissions of the newly-discovered gases could reverse this situation.
"The worry is if the two gases that are increasing continue on their trajectory, and one of them is actually accelerating, then it could counteract the measures of the Montreal Protocol," he said.
Dr Paul Fraser from CSIRO's Centre for Australian Weather and Climate Research, who was also involved in the study, said the source of the emissions is unknown.
"We know they are coming from the northern hemisphere, but that is as good as we know at this stage," Fraser said.
"It is good that we have found them quite early and that they haven't accumulated to a significant degree in terms of ozone-depletion. Now we are hoping to find out where they are coming from so their sources can be switched off."