Plugging an ozone hole : Ozone levels in the Arctic haven’t yet sunk to the extreme lows seen in Antarctica.

Plugging an ozone hole

by Staff Writers
Boston MA (SPX) Apr 17, 2014

File image.

Since the discovery of the Antarctic ozone hole, scientists, policymakers, and the public have wondered whether we might someday see a similarly extreme depletion of ozone over the Arctic.
But a new MIT study finds some cause for optimism: Ozone levels in the Arctic haven't yet sunk to the extreme lows seen in Antarctica, in part because international efforts to limit ozone-depleting chemicals have been successful.
"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," says Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT, and lead author of a paper published this week in the Proceedings of the National Academy of Sciences.
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.
A success story of science and policy
After 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.

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Massachusetts Institute of Technology

An aerial view of clouds over a mountain range in Greenland.

Courtesy of Michael Studinger/NASA Earth Observatory

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Courtesy of Michael Studinger/NASA Earth Observatory

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An Arctic ozone hole? Not quite

MIT researchers find that the extremes in Antarctic ozone holes have not been matched in the Arctic.

Audrey Resutek | Joint Program on the Science and Policy of Global Change
April 14, 2014
Since the discovery of the Antarctic ozone hole, scientists, policymakers, and the public have wondered whether we might someday see a similarly extreme depletion of ozone over the Arctic.
But a new MIT study finds some cause for optimism: Ozone levels in the Arctic haven’t yet sunk to the extreme lows seen in Antarctica, in part because international efforts to limit ozone-depleting chemicals have been successful.
“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,” says Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT, and lead author of a paper published this week in the Proceedings of the National Academy of Sciences.
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.
'A success story of science and policy'
After 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.

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NASA Pinpoints Causes of 2011 Arctic Ozone Hole

by Maria-Jose Vinas for NASA's Earth Science News Greenbelt MD (SPX) Mar 13, 2013

Maps of ozone concentrations over the Arctic come from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite. The left image shows March 19, 2010, and the right shows the same date in 2011. March 2010 had relatively high ozone, while March 2011 has low levels. Credit: NASA/Goddard.

A combination of extreme cold temperatures, man-made chemicals and a stagnant atmosphere were behind what became known as the Arctic ozone hole of 2011, a new NASA study finds. Even when both poles of the planet undergo ozone losses during the winter, the Arctic's ozone depletion tends to be milder and shorter-lived than the Antarctic's.
This is because the three key ingredients needed for ozone-destroying chemical reactions -chlorine from man-made chlorofluorocarbons (CFCs), frigid temperatures and sunlight- are not usually present in the Arctic at the same time: the northernmost latitudes are generally not cold enough when the sun reappears in the sky in early spring. Still, in 2011, ozone concentrations in the Arctic atmosphere were about 20 percent lower than its late winter average.
The new study shows that, while chlorine in the Arctic stratosphere was the ultimate culprit of the severe ozone loss of winter of 2011, unusually cold and persistent temperatures also spurred ozone destruction. Furthermore, uncommon atmospheric conditions blocked wind-driven transport of ozone from the tropics, halting the seasonal ozone resupply until April.
"You can safely say that 2011 was very atypical: In over 30 years of satellite records, we hadn't seen any time where it was this cold for this long," said Susan E. Strahan, an atmospheric scientist at NASA Goddard Space Flight Center in Greenbelt, Md., and main author of the new paper, which was recently published in the Journal of Geophysical Research-Atmospheres.
"Arctic ozone levels were possibly the lowest ever recorded, but they were still significantly higher than the Antarctic's," Strahan said. "There was about half as much ozone loss as in the Antarctic and the ozone levels remained well above 220 Dobson units, which is the threshold for calling the ozone loss a 'hole' in the Antarctic - so the Arctic ozone loss of 2011 didn't constitute an ozone hole."
The majority of ozone depletion in the Arctic happens inside the so-called polar vortex: a region of fast-blowing circular winds that intensify in the fall and isolate the air mass within the vortex, keeping it very cold.

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