A study has found four new man-made ozone-depleting gases in the atmosphere. The gases consist of three new chlorofluorocarbons (CFCs) and one new hydrochlorofluorocarbon (HCFC) that are being emitted despite the Montreal Protocol that called for a total ban of ozone-depleting gases by 2010.

The researchers from the University of East Anglia say loopholes are to blame for the continued use of CFCs and HCFCs and the source of these new gases are unknown.  Air samples that were trapped in polar firn (unconsolidated snow) were used to create a snapshot of the atmosphere that dates back a century. The century-old photo was then compared to samples collected between 1978 and 2012 from Tasmania, the site is used as the atmosphere there has been unaffected by pollution.

Based on the analysis, lead researcher Johannes Laube of the UEA said in a statement, “Our research has shown four gases that were not around in the atmosphere at all until the 1960s, which suggests they are man-made.”

CFCs are compounds made of chlorine, fluorine and carbon, notes the Environmental Protection Agency, which release chlorine atoms in the stratosphere when broken down by ultraviolet light. HCFCs were used as a way to replace CFCs but they also release ozone-depleting chlorine atoms in the atmosphere. CFCs and HCFCs were used as propellants and refrigerants.

The United Nation's Montreal Protocol was established in 1987, and enacted in 1989, following the discovery of a hole in the ozone layer over Antarctica. The international treaty banned the use of ozone-depleting substances, phasing out the use of CFCs and HCFCs with the goal of a total ban of the former by 2010 and the total ban of the latter by 2030. Based on these efforts, the thinning of the ozone layer, which protects humans from ultraviolet light, has reduced considerably and some believe it could be restored to 1950s levels by 2080, reports National Geographic.

There are loopholes and exemptions that allow for the use of CFCs but the three new gases are troubling, as they will take decades to break down, notes Laube, and CFCs are extremely effective at trapping heat, “often thousands of times more powerful than carbon dioxide,” reports Reuters.

The amount of ozone-depleting gas found by the researchers is not considered to be a threat to the ozone, notes Reuters, and is dramatically lower than the peak of CFC emissions in the 1980s. Around 74,000 metric tons of the new gases were emitted compared to the million metric tons of CFCs that were emitted before the ban.

For the researchers, the next step is identifying the source of these new gases. "We don’t know where the new gases are being emitted from and this should be investigated. Possible sources include feedstock chemicals for insecticide production and solvents for cleaning electronic components," said Laube. The research was published in Nature Geoscience.