CU-Boulder contingent headed for Sweden to conduct Arctic ozone loss experiments

November 28, 1999

A contingent of University of Colorado at Boulder faculty and students are descending on Kiruna, Sweden, to help undertake the largest field campaign ever to assess ozone concentrations and chemical changes in the Arctic stratosphere.

The four-month campaign involves about 200 researchers, students and support staff from the United States, Canada, Europe, Russia and Japan, said Professor Owen B. Toon of CU-Boulder's Laboratory for Atmospheric and Space Physics. Toon is one of five project scientists heading up the SAGE III Ozone Loss and Validation Experiment, or SOLVE, which also includes a cadre of satellites, aircraft, balloons and ground-based instruments operated by various countries.

"There were two previous Arctic ozone campaigns in 1988 and 1992, but this is the most comprehensive one yet," said Toon, the project scientist in charge of NASA's DC-8 aircraft that carries 16 instruments weighing about 40,000 pounds. "We will be able to see various types of data in real-time, allowing us to instantly change altitude and direction when we detect interesting atmospheric activity."

The aircraft will cruise at various altitudes, flying nearly 4,000 miles on each eight- to 10-hour mission over the Arctic, including the first-ever U.S. science forays over Sweden and Russia. The DC-8 will make about 25 flights during the campaign.

Toon will be plotting the courses and objectives of the DC-8 flights in response to observed atmospheric phenomena linked to the chemistry of seasonal ozone loss. Unlike the more severe winter ozone loss in the Antarctic stratosphere -- which appears to have bottomed out -- the ozone loss over the Arctic has been increasing steadily since 1995-1996, he said.

He also participated in selecting the instruments for the DC-8, which include a variety of spectrometers, lasers, gas chromatographs and other equipment to detect and measure clouds, ozone molecules, water vapor, hydroxyl radicals, carbon dioxide, halocarbons, particulates and nitric oxide.

Chlorine and bromine compounds released from man-made CFCs and halons during past decades are considered the primary cause of ozone depletion. But polar stratospheric clouds -- made up of ice and nitric acid and created within vortices that form at the poles each winter -- also play a key part, said Professor Margaret Tolbert of the CU-based Cooperative Institute for Research in Environmental Sciences.

"Chlorine in the atmosphere is normally tied up as chlorine nitrate or hydrochloric acid, both of which are nonreactive," she said. "But if there is a surface available to attach to -- in this case, polar stratospheric clouds -- then the chlorine compounds become reactive. In late winter and early spring, increasing sunlight reacts with these compounds to make the chlorine radicals that destroy ozone molecules." The use of CFCs worldwide was banned in 1986.

Toon and Tolbert, a husband-and-wife team, will conduct an investigation on aerosols and clouds in the stratosphere and troposphere as part of SOLVE. CU-Boulder doctoral student David Glandorf, who works in Tolbert's CU lab, will team up with scientists Bill Mankin and Mike Coffey of the National Center for Atmospheric Research to take infrared spectra of the clouds to determine their chemical make-up.

Another of Tolbert's doctoral students, Sarah Brooks, will work with NCAR scientists Bruce Gandrud and Darrel Baumgardner of Boulder using a high-flying ER-2 airplane to look at the light scattering of cloud particles to determine their size and composition. Doctoral student Megan Northway, from Tolbert's group, will work with a National Oceanic and Atmospheric Administration science team headed by David Fahey of Boulder to study reactive nitrogen species in the stratosphere. Peter Colarco, a doctoral student under Toon, will work with NASA scientists attempting to forecast the formation of polar stratospheric clouds.

"This gives our students the opportunity to combine lab work with valuable field experience in a very important international science campaign," Tolbert said.

In addition, LASP Assistant Professor Linnea Avalone is the chief scientist for a prototype instrument package to measure ozone, water vapor, C02 and halocarbons that will fly on the DC-8. The instruments are designed for use on commercial aircraft to collect valuable atmospheric data during routine flights.

LASP Research Associate Cora Randall will work with a U.S. Navy team to gather data daily on clouds, ozone, nitrogen dioxide and water using the Polar Ozone and Aerosol Measurement satellite. The information should give SOLVE scientists a better overall picture of the changing Arctic atmosphere.

Research Associate Mike Mills of LASP will work with Toon to model stratospheric aerosols, while Associate Professor Darren Toohey of CU's Program in Oceanic and Atmospheric Sciences will team with NOAA scientists to detect chlorine monoxide, the ozone-gobbling compound, with DC-8 instruments. Toohey also is the principal investigator on several balloon launches.

The first stage of SOLVE in November and December includes sampling the polar vortex circling the North Pole as it cools the air enough to form stratospheric clouds. Polar stratospheric clouds generally appear about 13 miles above Earth when temperatures dip to roughly minus 110 degrees Fahrenheit.

The second stage, in January and early February, will involve sampling the clouds and the beginning of stratospheric ozone loss, while the third stage -- lasting until mid-March -- will include observing the period of greatest ozone loss and the eventual break-up of the polar vortex.

The cold temperatures sustaining the clouds usually persist into early spring, when increased sunlight fuels ozone loss through catalytic reactions. But in the last several years, the clouds appear to have formed earlier and lingered longer.

"It could be that greenhouse gases are cooling the stratosphere, making the clouds persist for longer periods each winter," said Toon. Some computer models show that greenhouse gas warming on Earth's surface may not only lead to increased ozone loss, but also delay the expected recovery of the global ozone layer.

"This is going to be a very exciting mission, given the diverse groups of scientists, air crews, pilots, navigators, engineers and ground crews from different nations," said Toon. "Hopefully, when it is over we will better understand polar ozone processes and improve on our prediction capabilities."
Downloadable images of past Arctic ozone campaigns are available on the Web at

University of Colorado at Boulder

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