USA: While illegal emissions of the banned CFC11 have been identified in recent years, a new report points to higher emissions of the ozone-depleting gas, along with emissions of CFC12 and CFC113.
The new study by scientists at Massachusetts Institute of Technology (MIT) claims that estimates of new global CFC11 emissions is higher than previously reported. This is also the first study to quantify new global emissions of CFC12 and CFC113 and implies that new, illegal production of these CFCs has likely occurred in recent years.
“We find total emissions coming from new production is on the order of 20 gigagrams [20,000 tonnes] a year for each of these molecules,” said lead author Megan Lickley, a postdoc in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “This is higher than what previous scientists suggested for CFC11, and also identifies likely new emissions of CFC12 and 113, which previously had been overlooked.”
A study by the National Oceanic and Atmospheric Administration in 2018 revealed that despite a supposed global phase out in 2010, emissions of CFC11 has been rising again since 2013. Much of this was later traced to illegal manufacturing and use in the Chinese insulation industry.
In looking to improve the estimates of CFC lifetimes, the MIT researchers found that atmospheric lifetime of CFCs were shorter than current best-recommended values, suggesting emissions are likely higher than previously thought.
“Current best estimates of atmospheric lifetimes have large uncertainties,” said Lickley. “This implies that global emissions also have large uncertainties. To refine our estimates of global emissions, we need a better estimate of atmospheric lifetimes.”
Rather than consider the lifetimes and emissions of each gas separately, as most models do, the team looked at CFC11, 12, and 113 together, in order to account for similar atmospheric processes that influence their lifetimes (such as winds). These processes have been modelled by seven different chemistry-climate models, each of which provides an estimate of the gas’ atmospheric lifetime over time.
“We begin by assuming the models are all equally likely,” Lickley says. “Then we update how likely each of these models are, based on how well they match observations of CFC concentrations taken from 1979 to 2016.”
After including these chemistry-climate modelled lifetimes into a Bayesian simulation model of production and emissions, the team was able to reduce the uncertainty in their lifetime estimates. They calculated the lifetimes for CFC11, 12, and 113 to be 49 years, 85 years, and 80 years, respectively, compared with current best values of 52, 100, and 85 years.
“Because our estimates are shorter than current best-recommended values, this implies emissions are likely higher than what best estimates have been,” Lickley claims.
To test this idea, the team looked at how the shorter CFC lifetimes would affect estimates of unexpected emissions, particularly between 2014 and 2016. During this period, researchers previously identified a spike in CFC11 emissions and subsequently traced half of these emissions to eastern China. Scientists have since observed an emissions decrease from this region, indicating that any illegal production there has stopped, though the source of the remaining unexpected emissions is still unknown.
When Lickley and her colleagues updated their estimates of CFC bank emissions and compared them with total global emissions for this three-year period, they found evidence for new, unexpected emissions on the order of 20 gigagrams, or 20,000 tonnes for each chemical.
The results suggest that during this period, there was new, illegal production of CFC11 that was higher than previous estimates, in addition to new production of CFC12 and 113, which had not been seen before.
Prior to their global phaseout under the Montreal Protocol, CFCs were widely used in the manufacturing of refrigerants, aerosol sprays, chemical solvents, and building insulation. Both CFC11 and CFC12 were widely used in the refrigeration and air conditioning industry.
The report is published here.
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