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Study assesses likelihood of Arctic ozone hole

This year's ozone hole over Antarctica was the second-smallest in 20 years, according to NASA.

Last year’s ozone hole over Antarctica was the second-smallest in 20 years, according to NASA.

CFC ban showing signs of success

Staff Report

FRISCO — Scientists say it’s unlikely that the Arctic will see ozone depletion on the scale of the Antarctic ozone hole, thanks mainly to international efforts to limit ozone-killing chemicals.

“While there is certainly some depletion of Arctic ozone, the extremes of Antarctica so far are very different from what we find in the Arctic, even in the coldest years,” said MIT atmospheric scientists Susan Solomon.

“It’s really a success story of science and policy, where the right things were done just in time to avoid broader environmental damage,” said Solomon, who made some of the first measurements in Antarctica that pointed toward CFCs as the primary cause of the ozone hole.

Frigid temperatures can spur ozone loss because they create prime conditions for the formation of polar stratospheric clouds. When sunlight hits these clouds, it sparks a reaction between chlorine from chlorofluorocarbons (CFCs), human-made chemicals once used for refrigerants, foam blowing, and other applications — ultimately destroying ozone.

When the ozone-attacking properties of CFCs were discovered in the 1980s, countries across the world agreed to phase out their use as part of the 1987 Montreal Protocol treaty. While CFCs are no longer in use, those emitted years ago remain in the atmosphere. As a result, atmospheric concentrations have peaked and are now slowly declining, but it will be several decades before CFCs are totally eliminated from the environment — meaning there is still some risk of ozone depletion caused by CFCs.

To obtain their findings, the researchers used balloon and satellite data from the heart of the ozone layer over both polar regions. They found that Arctic ozone levels did drop significantly during an extended period of unusual cold in the spring of 2011. While this dip did depress ozone levels, the decrease was nowhere near as drastic as the nearly complete loss of ozone in the heart of the layer seen in many years in Antarctica.

The MIT team’s work also helps to show chemical reasons for the differences, demonstrating that ozone loss in Antarctica is closely associated with reduced levels of nitric acid in air that is colder than that in the Arctic.

“We’ll continue to have cold years with extreme Antarctic ozone holes for a long time to come,” Solomon said. “We can’t be sure that there will never be extreme Arctic ozone losses in an unusually cold future year, but so far, so good — and that’s good news.”

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