Published: Thu, May 17, 2018
Research | By Raquel Erickson

Banned ozone-destroying chemical makes a mysterious resurgence

Banned ozone-destroying chemical makes a mysterious resurgence

Atmospheric levels of a key ozone-depleting chlorofluorocarbon (CFC) are not going down as fast as they should be, researchers in the U.S. have discovered.

According to global CFC-11 levels measured by scientists at NOAA and Cooperative Institute for Research in Environmental Sciences (CIRES), the concentration of the chemical declined at an accelerating rate till 2002, but then, the fall became stagnant for nearly a decade. Production was banned, emissions fell and the hole shriveled. "I've been making these measurements for more than 30 years, and this is the most surprising thing I've seen", says lead researcher Stephen Montzka at the NOAA, which monitors chemicals in the atmosphere.

If rogue production continues, it might just hold back the fragile recovery of Earth's vital ozone shield, despite years of success. CFC-11 was originally used as a refrigerant but was banned in 1987 under the Montreal Protocol, the worldwide agreement created to protect the ozone layer.

To be clear, CFC-11 concentrations in the atmosphere are still declining, but they're declining significantly more slowly because of the possible new source as compared to if there was none. "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.

The researchers built mathematical models to account for these observations, which suggest CFC-11 emissions have actually been increasing by around 25% each year since 2012, despite virtually no CFC-11 production being reported to the relevant authorities during this time. It is only destroyed in the stratosphere, some 9 to 18 miles above the planet's surface, where the resulting chlorine molecules engage in a string of ozone-destroying chemical reactions.

"It is therefore imperative that this finding be discussed at the next Ministerial meeting of Governments given recovery of the ozone layer is dependent on all countries complying with the Montreal Protocol (and its adjustments and amendments) with emissions globally dropping to zero".

The team said the emissions were most likely due to new, unreported production from an unidentified source in East Asia.

David Fahey, director of NOAA's Chemical Science Division and co-chair of the United Nations Environment Programme's Ozone Secretariat's Science Advisory Panel, said ongoing monitoring of the atmosphere will be key to ensuring that the goal of restoring the ozone layer is achieved. "It's therefore critical that we identify the precise causes of these emissions and take the necessary action". "They should tell the industries that's not going to work". "A delay in ozone recovery [.] is anticipated, with an overall importance depending on the trajectory of CFC-11 emissions and concentrations in the future". Even more unexpected was that the rate of decline slowed by 50% after 2012.

But there a growing scientific doubts about the progress of healing in the ozone hole.

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