Scientists discover secret polluters may be eroding the ozone layer

One of humanity's few global environmental triumphs has been our work towards protecting the ozone layer.

The ozone layer shields us from harmful ultraviolet rays of the Sun. And after the discovery in the 1970s that chloroflourocarbons, a group of man-made chemicals, were destroying it, we actually did something about it.  

Yet even with productions going to zero, the emissions of CFC-11 were sustained at a constant level for some reason we didn't understand.- Stephen Montzka

In the late 1980s governments around the world agreed to phase out production of these ozone-depleting chemicals in the Montreal Protocol — often celebrated as the most successful international environmental agreement in history.

Ozone levels stabilized by the mid-1990s and began to recover in the 2000s. It was a job well done, a problem on its way to being solved.

• Research paper in the journal Nature

But last week, scientists announced they'd detected a large spike in the atmospheric levels of the ozone-destroying chemical CFC-11. It was a shocking discovery for Dr. Stephen Montzka, a scientist with the National Oceanic and Atmospheric Administration (NOAA) in the United States, who led the team.

"We came to the conclusion that emissions of CFC-11 have increased since the 2012 period," said Montzka. The data suggests to him that someone may have started producing the banned chemical again.

CFC-11 is the second most abundant ozone-depleting gas controlled by the Montreal Protocol. It's part of the CFC family of chemicals, which were widely used during the mid-1900s as foam blowing agents, propellants for bug sprays and aerosol sprays, and inexpensive coolants for air conditioners and refrigerators. During its peak, more than 1 million metric tons of CFCs were produced annually, and annual sales reached $1 billion.

While they're safe to use in industrial applications and remain inert in lower atmosphere, they undergo chemical reactions once they reach the stratosphere, which destroy ozone.

The global concentration of CFC-11 peaked in the early '90s, according measurements done by NOAA since the '70s, but has been falling ever since. The reported production amounts to the United Nations Environmental Programme pretty much became zero by 2008, according to Montzka. "Yet even with productions going to zero, the emissions of CFC-11 were sustained at a constant level for some reason we didn't understand."

"Beginning in 2013, CFC-11 concentration began decreasing more slowly, rather than more rapidly," said Montzaka. Concentrations declined only half as fast over the past three years compared to the rate measured during the previous decade, which was substantially slower than expected.

This suggested there was an emission increase, which baffled Montzka. So he did more tests and concluded that the extra emissions probably came from new productions of CFC-11.

"We looked carefully at what the emission increase might imply about CFC-11 being emitted from the large reservoir of material that still exists in foams, in buildings, in refrigerators, and things like that," said Montzka. This material gets released as buildings are demolished, and fridges leak. But this legacy production simply couldn't account for the new emissions they were observing. "That seems to make no sense."

They tried to determine the source of the new emissions, and narrowed it down to Eastern Asia. Beginning in 2013, they observed an increased concentration of CFC-11 in the polluted air reaching Hawaii. Analysis suggests the plumes came from Eastern Asia.

"We're not sure why they're doing this." said Montzaka. "There are substitutes chemicals that presumably have been in use for many years. Some of them are more expensive to produce than CFC-11, but others are less expensive."

A quick Google search also found that there are banned CFC products still being sold online. 

Since 2013, about 13 kilotons of CFC-11 were being emitted each year. "If these emissions were to go away soon, then the influence on the ozone is probably going to be minor," said Montzka. "But if they were to persist for the next 30, 40 years, then it would probably delay the recovery of the ozone layer by about 10 years."

• 'Father of global warming' worries the climate young people inherit will be out of their control
• Trump is losing the 'war on coal' to the free market
• What happens when you warm the Antarctic seabed by 1 degree
• The Great Barrier Reef sounds sick, so baby fishes aren't attracted to it

Is this a failure of the Montreal Protocol? Not so, according to Montzka. "I'm shocked and surprised by the findings, but not disappointed in the Montreal Protocol," he said.

"It still remains one of the most successful international protocols, and we need to remember that the concentration of ozone-depleting gases are still going down, just a little less rapidly than they might have been."

He has confidence in the systems that the Montreal Protocol has put in place. If it comes to it, he thinks they'll be ready to deal with the problem.  

The best way to find the culprit is probably to collaborate with scientific institutions in Eastern Asia, Montzka suggested. If they've also been tracking CFC-11 levels over time in their respective regions, then the data could lead them to the scene of the crime.

"The state of our understanding of interpretation of those measurements is that we'll be able to pinpoint the location precisely."