High Emissions from Feedstocks and Aged Equipment are Delaying Ozone Recovery

Washington, DC, December 2, 2024 – A new study published in Atmospheric Chemistry and Physics reveals a 17-year delay in the projected recovery of the ozone layer since 2006, underscoring the need for enhanced global environmental policies and enforcement.  The recovery date is an estimated year when the key ozone-depleting gases will be back to 1980 levels. Estimated recovery dates provide a benchmark for measuring progress on the global coordinated effort to reduce emissions of ozone-depleting chemicals. The findings are part of a comprehensive analysis led by Georgetown University Earth Commons scientist Megan Lickley and co-authored by University of Maryland Earth System Science Interdisciplinary Center professor Ross Salawitch alongside an international team of researchers.

The study focuses on the recovery of equivalent effective stratospheric chlorine (EESC), a critical metric for estimating stratospheric ozone depletion, and explores why the timeline projected by the scientific assessment of EESC returning to pre-1980 levels has been extended from 2049 as of a 2006 report to 2066, as reported in 2022.

Researchers identified key contributors to this delay, including changes in modeling assumptions, unanticipated emissions, and larger-than-expected sources of lawfully produced ozone-depleting substances (ODS) —some manufactured recently to be used as feedstock, others leaking from old equipment—are significantly delaying the recovery of the ozone layer. Subsequent revised calculations of ODS’ atmospheric lifetimes and updates to historical emissions estimates accounted for part of the delay.

“The 2022 International Scientific Assessment of Ozone Depletion showed that our expected return date was now 17 years later than the 2006 assessment had projected, and this delay caused us to wonder, ‘why’?” said Lickley. “Our paper shows that part of the delay is due to improved understanding of how long these chemicals last in the atmosphere, as well as how we estimate their precise impact on ozone depletion. However, another very important part of this delay is that humans have emitted more of these chemicals into the atmosphere than had initially been anticipated.”

Undocumented production of ODSs, such as carbon tetrachloride and CFC-11, further contributed to the delay, reflecting gaps in compliance and monitoring under the Montreal Protocol. Updated calculations revealed significant reservoirs of CFC-11 and other ODSs in old equipment that continue to emit harmful agents into the atmosphere, delaying ozone recovery by years.

“Our study shows that the ozone layer will not recover as quickly as had once been expected due to depletion caused by human release of ozone depleting substances,” says Salawitch, who also holds appointments in the departments of Atmospheric and Oceanic Science and Chemistry and Biochemistry. The ozone layer protects the ecosystem, including humans, animals, and crops, from harmful solar ultraviolet radiation. A delay in the recovery of the ozone layer means that higher amounts of solar UV will reach Earth’s surface than would have occurred without the emission of these pollutants, with a number of deleterious effects including higher rates of human skin cancers.”

The study highlights opportunities for accelerating ozone recovery through tighter controls on feedstock emissions and aged equipment, enhanced monitoring and enforcement mechanisms, and efforts to recover and safely destroy existing ODS stocks from equipment and foam applications.

Lickley concludes that, while the Montreal Protocol helped avoid catastrophic ozone loss, and while cheating on protocols has been shown to play only a minor role in further ozone depletion, “Ongoing scientific work, continued monitoring of the atmosphere, and updating of the Montreal Protocol agreement when called for are all necessary to ensure progress.”

The full study and additional information is available at Atmospheric Chemistry and Physics.