Huge Losses Found in Arctic Ozone Layer

By Cat Lazaroff

WASHINGTON, DC, April 6, 2000 (ENS) - More than 60 percent of the ozone layer blanketing the Arctic Circle was lost this past winter, due to record cold and continued pollution by humans, scientists from the United States and the European Union said Wednesday. The researchers also warned that global warming may speed up ozone loss and slow the recovery of the ozone layer.


A computer generated image of the thinning ozone layer, with the thinnest areas shown in dark blue (All photos courtesy NASA)
The ozone losses are likely to affect the ozone levels over Europe during spring, the scientists said.

Studies by the National Aeronautics and Space Administration (NASA) and the European Union have revealed ozone losses of over 60 percent in the Arctic stratosphere around 18 kilometers (11 miles) above the Earth, during one of the coldest stratospheric winters on record. This is one of the most substantial ozone losses at this altitude ever recorded in the Arctic.

"Last winter's results have heightened concerns that ozone levels over the north polar region may continue to decline despite the benefits of international agreements to stop production and release of ozone-destroying chemicals," said Dr. Hanjürg Jost of NASA's Ames Research Center, located in California's Silicon Valley.

More than a decade ago scientists determined that ozone depletion is caused mostly by man-made chlorine and bromine compounds. Manufacturers made the chlorine compounds, chlorofluorocarbons or CFCs, for use as refrigerants, aerosol sprays, solvents and foam-blowing agents. Fire fighters used bromine-containing halons to put out fires. Manufacture of chlorofluorocarbons ceased in 1996 in developed countries under the terms of the Montreal Protocol and its amendments.

But climate change in the stratosphere will likely result in increased ozone losses in the Arctic winter in the coming decades, even as the amount of chlorine and bromine introduced into the atmosphere is decreased, the researchers said. The buildup of greenhouse gases, such as carbon dioxide, tends to trap more heat near the Earth's surface, while at the same time colder than normal temperatures are experienced in the stratosphere, where the ozone breakdown occurs, scientists explained.


Opalescent polar stratospheric clouds help turn chlorine into the ozone destroyer chlorine monoxide
The cold air helps form high altitude clouds (at about 18 kilometers or 60,000 feet), called "polar stratospheric clouds" or PSCs, which play a unique role in atmospheric ozone loss. The opalescent clouds form only in the cold temperatures found at the poles. These clouds help trigger the conversion of chlorine from relatively non-reactive forms to a form (chlorine monoxide, or ClO) that, in combination with sunlight, destroys ozone.

PSCs were observed to extend widely over the Arctic region from early December to early March. "We were somewhat surprised to see PSCs so early in December," said Dr. Mark Schoeberl, who was the SOLVE co-project scientist for observations made from NASA's DC-8 aircraft. "Some of the PSC types and their locations which we observed in December did not fit within our current understanding."

The last PSCs were observed on March 8 by instruments aboard the DC-8, and on March 15 by satellite.

The polar stratosphere temperatures were extremely low over the course of this last winter. At 20 kilometers (66,000 feet) on January 28, the area covered by temperatures low enough to form PSCs was 14.8 million square kilometers (5.7 million square miles), which is larger than the continental United States. This is the largest area coverage recorded in more than 40 years of Northern Hemisphere stratospheric analyses.

"The polar stratospheric clouds covered a larger area, and persisted for a longer period of time, than for any other Arctic winter during the past 20 years. These conditions heighten our concern regarding possible couplings between climate change and stratospheric ozone depletion," said ozone researcher Dr. Ross Salawitch of NASA's Jet Propulsion Laboratory, Pasadena, California.


One of NASA's DC-8 aircraft prepares for a data gathering flight
The mixing of polar air into middle latitudes, both during the winter and as the polar circulation broke down in late March, influences ozone levels over the populated middle regions, particularly in Europe.

In March, the World Meteorological Organisation Mapping Centre at the University of Thessaloniki reported that the average ozone amounts over Europe were 15 percent below the pre-1976 average, lending credence to concerns that thinning ozone will significantly impact species living outside the Arctic Circle.

More than 350 researchers from the United States, Europe, Canada, Russia and Japan took part in the combined NASA/European Union-sponsored field campaign, said project manager Mike Craig of NASA Ames. Researchers measured ozone, other atmospheric gases, particle amounts and air motions in the Arctic stratosphere, the atmospheric layer between roughly eight and 50 kilometers (five to 31 miles) altitude.

From November 1999 to March 2000, investigators used spacecraft, aircraft, large, small and long-duration balloons, and ground-based instruments to gather data. The aircraft and large balloon launch teams were based in Kiruna, Sweden.

A National Oceanic and Atmospheric Administration ozone instrument aboard NASA's high altitude ER-2 aircraft was used to measure ozone losses in the lower stratosphere. Data from the ER-2 show ozone in the Arctic decreasing by about 60 percent between January and mid-March, said ER-2 co-project scientist Paul Newman of NASA's Goddard Space Flight Center.


Researchers prepare to send an instrument package up on a weather balloon
These measurements are comparable to the large ozone losses in the lower stratosphere observed during several winters in the mid-1990s. Total ozone losses throughout the depth of the atmosphere were slightly reduced because ozone losses were smaller above 66,000 feet (20 kilometers). Spacecraft observations by NASA's Total Ozone Mapping Spectrometer-Earth Probe clearly showed an area of low ozone over the polar region during February and March.

The average total polar ozone for the first two weeks of March was 16 percent lower than scientists observed during the same time period in the early 1980s.

The campaign - the biggest field measurement campaign yet undertaken - included the NASA-sponsored Stratospheric Aerosols and Gas Experiment (SAGE III) Ozone Loss and Validation Experiment (SOLVE), and European Union-sponsored Third European Stratospheric Experiment on Ozone (THESEO-2000).


A weather balloon heads for the Arctic stratosphere
The joint investigations into the Arctic stratosphere have provided better insights into the processes that control polar ozone. These insights considerably add to scientists' ability to predict ozone levels in the future as chlorine levels decline and as greenhouse gases increase.

"European cooperation within an international team has made it possible to achieve these research results," said Research Commissioner Philippe Busquin. "They will provide the best possible scientific advice to the regulatory process concerning ozone depleting substances in the framework of the Montreal Protocol and, equally important, to the citizens."