The recovery of the ozone layer in the Earth’s stratosphere could be delayed by several years, according to an international study led by Empa. <\/p>\n\n\n\n
The cause is persistent emissions of so-called feedstock chemicals, which are still permitted as raw materials in industry. These ozone-depleting substances have so far been excluded from international agreements because, according to the current study, their emissions and use have been significantly underestimated.<\/p>\n\n\n\n
Although ozone-depleting chemicals such as carbon tetrachloride (CCl\u2084) or certain chlorofluorocarbons (CFCs) are no longer used in refrigerators and foams, they continue to serve as feedstocks in industrial processes for the production of modern refrigerants and plastics. Until now, these so-called feedstock chemicals have flown under the radar of international agreements because the quantities produced and leakage rates were significantly underestimated.<\/p>\n\n\n\n
Working with international research groups, Empa researchers have now used global measurements to show that during the production and processing of these substances, approximately three to four percent escapes into the atmosphere through leaks. Furthermore, their use has increased significantly in recent decades. In a study published in Nature Communications, they have now calculated that, as a result, the ozone layer is likely to recover about seven years later than previously assumed \u2013 unless emissions are reduced. \u201cThese substances are not only ozone-depleting but also highly harmful to the climate. Lower emissions would thus benefit both the ozone layer and the climate,\u201d says Stefan Reimann, an atmospheric scientist at Empa and lead author of the study.<\/p>\n\n\n\n
When the Montreal Protocol was negotiated in the 1980s and later strengthened, it led to a global ban on ozone-depleting substances in everyday products. Feedstock chemicals, however, were exempt from this ban. At the time, industry assumed that only about 0.5 percent of the quantities produced would escape into the atmosphere and that the use of these substances would decline in the long term. \u201cBut this assessment has not been accurate anymore for quite some time,\u201d says Reimann. \u201cFeedstock chemicals are now being released in increased quantities during production, transport, and further processing, and the volumes currently being produced are significantly larger than was assumed 30 years ago.\u201d<\/p>\n\n\n\n
These new findings are based on global atmospheric measurements from international networks such as the Advanced Global Atmospheric Gases Experiment (AGAGE), which includes the Empa research station on the Jungfraujoch. Since many ozone-depleting substances remain in the atmosphere for decades, their concentrations allow conclusions to be drawn about global emissions. \u201cWe measure the concentrations of these substances in the atmosphere. Based on their lifetimes, we can calculate how much they should actually be decreasing. If they aren\u2019t, emissions must still be occurring,\u201d explains Martin Vollmer, an Empa researcher and co-author of the study.<\/p>\n\n\n\n
A comparison of these measurements with the production figures officially reported by individual countries shows that today, an average of three to four percent of the feedstock produced enters the atmosphere \u2013 several times the originally assumed values. For carbon tetrachloride, which is particularly harmful to the ozone layer, emission rates are even above four percent.<\/p>\n\n\n\n