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CFCs MAY SPEND LESS TIME IN ATMOSPHERE THAN THOUGHT
New results are pointing to unexpected and illegal production of several CFCs over recent years .
MIT scientists have found that ozone-depleting chlorofluorocarbons , or CFCs , stay in the atmosphere for a shorter amount of time than previously estimated . Their study suggests that CFCs , which were globally phased out in 2010 , should be circulating at much lower concentrations than what has recently been measured .
The new results , published today in Nature Communications , imply that new , illegal production of CFCs has likely occurred in recent years . Specifically , the analysis points to new emissions of CFC-11 , CFC-12 , and CFC-113 . These emissions would be in violation of the Montreal Protocol , the international treaty designed to phase out the production and consumption of CFCs and other ozone-damaging chemicals .
The current study ’ s estimates of new global CFC-11 emissions are higher than what previous studies report . This is also the first study to quantify new global emissions of CFC-12 and CFC-113 .
“ We find total emissions coming from new production is on the order of 20 gigagrams a year for each of these molecules ,” says 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 CFC-11 , and also identifies likely new emissions of CFC-12 and 113 , which previously had been overlooked . Because CFCs are such potent greenhouse gases and destroy the ozone layer , this work has important implications for the health of our planet .”
The study ’ s co-authors include Sarah Fletcher at Stanford University , Matt Rigby at the University of Bristol , and Susan Solomon , the Lee , and Geraldine Martin Professor of Environmental Studies in MIT ’ s Department of Earth , Atmospheric and Planetary Sciences .
BANKING ON LIFETIMES Prior to their global phase-out , CFCs were widely used in the manufacturing of refrigerants , aerosol sprays , chemical solvents , and building insulation . When they are emitted into the atmosphere , the chemicals can loft to the stratosphere , where they interact with ultraviolet light to release chlorine atoms , the potent agents that erode the Earth ’ s protective ozone .
Today , CFCs are mostly emitted by ‘ banks ’ — old refrigerators , air conditioners , and insulation that were manufactured before the chemical ban and have since been slowly leaking CFCs into the atmosphere . In a study published last year , Lickley and her colleagues calculated the amount of CFCs still remaining in banks today .
Massachusetts Institute of Technology
The results suggest that during this period , there was new , illegal production of CFC-11 that was higher than previous estimates , in addition to new production of CFC-12 and 113 , which had not been seen before .
They did so by developing a model that analyses industry production of CFCs over time , and how quickly various equipment types release CFCs over time , to estimate the amount of CFCs stored in banks . They then incorporated current recommended values for the chemicals ’ lifetimes to calculate the concentrations of bank-derived CFCs that should be in the atmosphere over time . Subtracting these bank emissions from total global emissions should yield any unexpected , illegal CFC production . In their new paper , the researchers looked to improve the estimates of CFC lifetimes .
“ Current best estimates of atmospheric lifetimes have large uncertainties ,” Lickley says . “ This implies that global emissions also have large uncertainties . To refine our estimates of global emissions , we need a better estimate of atmospheric lifetimes .”
UPDATED SPIKE Rather than consider the lifetimes and emissions of each gas separately , as most models do , the team looked at CFC-11 , 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 chemistryclimate 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 .”
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