Scientists develop a new method to assess the recovery of the ozone layer

Researchers have developed a new method to assess the impacts of ozone-depleting substances that threaten the recovery of the ozone layer.

Published in the journal Naturetheir method – the integrated measurement of ozone layer depletion (IOD) – provides a useful tool for policy makers and scientists.

The IOD was designed to provide a simple way to measure the effects of unregulated emissions of ozone depleting substances and to assess the effectiveness of ozone layer protection measures.

The ozone layer is found in a region of the Earth’s atmosphere known as the stratosphere and acts as an important protective barrier against most of the sun’s harmful ultraviolet rays.

Ozone-depleting gases such as chlorofluorocarbons, better known as CFCs, have been phased out under the Montreal Protocol – an international treaty agreed to protect the ozone layer.

The Montreal Protocol has been largely successful, but illegal violations undermine its effectiveness.

The IOD indicates the impact of any new emission on the ozone layer taking into account three elements: the strength of the emission, the duration of its stay in the atmosphere and the amount of ozone it destroys chemically.

For environmental protection and human health policies, the IOD represents a simple way to calculate the impact of a given emission scenario on ozone recovery.

This new metric was developed by researchers from the National Center for Atmospheric Science at the University of Cambridge and the National Center for Earth Observation at the University of Leeds.

Professor John Pyle, of the National Center for Atmospheric Science and the University of Cambridge, has spent his career studying ozone depletion in the stratosphere and developing the Montreal Protocol. He is the main author of the current Nature paper.

“Following the Montreal Protocol, we are now in a new phase – assessing the recovery of the ozone layer,” said Pyle, from the Yusuf Hamied Department of Chemistry at Cambridge. “This new phase calls for new metrics, like Integrated Ozone Depletion – which we call the IOD. Our new metric can measure the impact of emissions – regardless of their size. Using a computer model of atmospheric chemistry, we were able to show a simple linear relationship between IOD, emission size and chemical lifetimes, so with knowledge of the lifetimes it is straightforward to calculate the ‘IOD, making it an excellent measure for both science and policy.

The Montreal Protocol successfully protects the ozone layer, but there is growing evidence to suggest that the ozone hole is recovering more slowly than expected.

“IOD will be very useful for monitoring ozone recovery, and particularly relevant for regulators who need to phase out substances that can chemically destroy ozone,” Pyle said.

The IOD metric was created using a computer model of the atmosphere, called the UK Chemistry and Aerosols (UKCA) model. The National Center for Atmospheric Science and the Met Office developed the UKCA model to calculate future projections of important chemicals, such as ozone, into the stratosphere.

“We used the UKCA model to develop the IOD metric, which will allow us to estimate the effect of any new illegal or unregulated emissions on the ozone layer. In the UKCA model, we can experiment with different types and concentrations of CFCs and other ozone-depleting substances,” said co-author Dr Luke Abraham, also from the University of Cambridge. “We can estimate how chemicals in the atmosphere will change in the future and assess their impact on the ozone layer over the next century.”

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