As described in the journal Nature Communications, 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.
Researchers have now used global measurements to calculate that, as a result, the ozone layer is likely to recover about seven years later than previously assumed - unless emissions are reduced.
Members of the Atmospheric Chemistry Research Group at the University of Bristol used atmospheric transport models to track these chemicals as they move through the atmosphere. By comparing their simulations with long‑term measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE), a network Bristol has been involved in since 1978, they were able to derive global emissions estimates.
“The measurements show that emissions linked to fluorochemical production are substantially higher than expected," said Professor Rigby. "This suggests much greater leakage of ozone‑depleting and climate‑warming gases than the controls of the Montreal Protocol assumed, with clear implications for climate change and ozone layer recovery."