Arctic Ozone Thins

March 17, 2011

Unusually chilly temperatures in part of the Arctic atmosphere, iridescent ice clouds and the ongoing presence of ozone-depleting substances are triggering significant depletion of the protective ozone layer, according to recent, ongoing observations by NOAA scientists and international colleagues.

“This is pretty sudden and unusual,” said Bryan Johnson, a research chemist in the Global Monitoring Division of NOAA’s Earth System Laboratory (ESRL), and leader of ESRL’s Ozonesonde Group.

Aidan Colton at NOAA's Mauna Loa Observatory demonstrates how early flask samples were filled at the site.

Photo credit: Seth White/UNAVCO

Icy and high-altitude polar stratospheric clouds. Ozone-depleting chemical reactions can take place on the ice crystals in these clouds.

The stratospheric ozone layer protects Earth from damaging ultraviolet radiation, but chlorine and bromine from air pollutants such as chlorofluorocarbons and similar compounds can eat away at ozone in the right conditions: Temperatures below -78C (cold enough to form nitric acid-containing ice crystals in the relatively dry atmosphere) and sunlight (to trigger chemical reactions on ice surfaces).

Earth’s best-known ozone hole forms with the return of sunlight in the Antarctic spring every year (September), when total ozone levels can drop from 250-300 Dobson units to just above 100. Springtime above the Arctic is usually far less eventful, but this year, the so-called polar vortex winds have kept the region very cold at high altitudes.

“The Arctic vortex is holding together, keeping stratospheric temperatures cold enough for these ice clouds to stay around” Johnson said. “As sunlight returns, it all comes together to trigger significant thinning of the ozone.”

Total column ozone measurements in the Arctic, normally 400 Dobson units this time of year, were down to 310 Dobson units last week. And although the thinner ozone means more radiation can hit Earth’s surface, levels in the Arctic remain higher than elsewhere, Johnson said. Ozone levels are normally lower in equatorial regions, for example, meaning Spring Break travelers in Mexico are baring skin under an ozone blanket of about 270 Dobson units.

The unusual Arctic depletion this year means Johnson and his colleagues are making arrangements to take observations more frequently. NOAA scientists typically release ozonesondes (giant balloons carrying ozone instruments) weekly this time of year, from the National Science Foundation’s Summit Station in Greenland. The researchers have enough supplies on site to send up ozonesondes at least twice weekly for the next few weeks, Johnson said, and NSF and contractor CH2MHill Polar Field Services are assisting in the logistics by planning to send in more balloons next month, to replenish depleted supplies.

International scientists at other locations around the Arctic have also taken note of dropping levels, and are increasing observation frequency.

Stratospheric ozone varies from year-to-year, although satellite and radiosonde measurements show a long-term cooling trend in stratospheric temperatures. Climate models predict cooling of the stratosphere, along with warming at Earth’s surface.

Read a Q&A interview with Bryan Johnson.

Related Links

ESRL's ozone pages

Data from NOAA's Greeland ozonesondes

The National Science Foundation’s Summit Greenland Observatory

News from the Potsdam Research Unit of the Alfred Wegener Institute in Germany (which coordinates ozone measurements made at more than 30 stations in the Arctic and Subarctic)

The Scientific Assessment of Ozone Depletion: 2010