The rise in CFC-11 was revealed by Stephen Montzka, at the US National Oceanic and Atmospheric Administration (NOAA) in Colorado, and colleagues who monitor chemicals in the atmosphere. Samples acquired in Hawaii lead to speculation that the CFC-11 production may be happening in East Asia, but an exact source isn't clear at this time.
CFC-11 is an ozone-depleting chemical whose phase out agreed upon in the '80s and has been under an global ban since 2010.
The findings, published in the journal Nature, show that since 2012, the rate of decline for a substance known as CFC-11 has slowed, and Montzka's research suggests new emission sources may have popped up over East Asia. "In the end, we concluded that it's most likely that someone may be producing the CFC11 that's escaping to the atmosphere", he said.
Thirty years or more ago CFC11 (R11) was commonly used as a refrigerant and insulation propellant. Use of the chemical was banned in 2010 via the Montreal Protocol, an worldwide agreement made to protect the environment.
Countries have reported close to zero production of the chemical since 2006 but the study found about 14,300 tons (13,000 metric tons) a year has been released since 2013.
Because CFC-11 still accounts for one-quarter of all chlorine present in today's stratosphere, expectations for the ozone hole to heal by mid-century depend on an accelerating decline of CFC-11 in the atmosphere as its emissions diminish- which should happen with no new CFC-11 production.
The study authors point out that while CFC-11 can persist in the atmosphere for 50 years, the overall level of chlorine atoms is still declining.
It is possible that the increased emissions could be due to older buildings being demolished, but that doesn't seem to be the case. This conclusion was confirmed by other changes recorded in NOAA's measurements during the same period, such as a widening difference between CFC-11 concentrations in the northern and southern hemispheres - evidence that the new source was somewhere north of the equator.
The USA ceased production in 1996 and other countries agreed to phase out CFC production by 2010.
"You are left with, boy, it really looks like somebody is making it new", said Montzka, who noted that the less damaging replacement for CFC-11 is more expensive to make. CFC-11 concentrations have declined by 15 percent from peak levels measured in 1993 as a result. Scientists say there's more of it - not less - going into the atmosphere and they don't know where it is coming from.
He calls it "rogue production", adding that if it continues "the recovery of the ozone layer would be threatened".
The findings of Montzka and his team of researchers from the Cooperative Institute for Research in Environmental Sciences (CIRES), the United Kingdom, and the Netherlands, represent the first time that emissions of one of the three most abundant, long-lived CFCs have increased for a sustained period since production controls took effect in the late 1980s. If not remedied soon, however, substantial delays in ozone layer recovery could be expected, Montzka said.
"The analysis of these extremely precise and accurate atmospheric measurements is an excellent example of the vigilance needed to ensure continued compliance with provisions of the Montreal Protocol and protection of the Earth's ozone layer", Fahey said.