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Nov 4, 2012 6:48 PM by Natalie Noah

From Discovery, To Solution, To Evolution: Observing Earth's Ozone Layer

Remember the ozone hole? A signature environmental concern of the 1980s has become a signature environmental success story. While a strong international treaty regulates ozone-depleting substances, scientists at NASA and NOAA continue to keep a close eye on the evolving state of ozone in the atmosphere.

Yes, an ozone hole above Antarctica still forms each year - just six years ago in 2006 it reached its largest size ever, covering more than 11 million square miles. The ozone hole this year is back, but is somewhat smaller than in the past because of the usual variations in Antarctic weather conditions. In the long term, worldwide adherence to the Montreal Protocol and its amendments has scientists expecting that the ozone layer will once again reach full strength - but they don't expect a return to 1980 global levels until 2050. The ozone hole itself could be completely eliminated by 2065. It will be a slow recovery and there may be obstacles along the way.

While the Montreal Protocol may have averted disaster, the ozone layer remains in flux, and will stay in the sights of atmosphere-observing satellites for a long time.

Satellite instruments that provide measurements of atmospheric ozone, such as the Ozone Mapping Profiler Suite (OMPS) on the Suomi National Polar-orbiting Partnership satellite and continuing on the Joint Polar Satellite System (JPSS) will become even more important as international ground-based measurement programs are being scaled back because of government budget cuts. The JPSS program will ensure continuity of OMPS for nearly the next 20 years.

The Antarctic Ozone Hole

In 1957, the British Antarctic Survey began routine observations at the Halley Bay ground station to better understand the Antarctic ozone layer. Their Dobson spectrophotometer measured the total amount of ozone between the surface and space over the station. In 1974, Drs. Mario Molina and F. Sherwood Rowland theorized that the chlorine from chlorofluorocarbons (CFCs) could lead to ozone depletion; they later won the 1995 Nobel Prize for their contributions. In 1985, the British science team published results that revealed a sharp decline in ozone in the Antarctic spring. We had a problem: Above Antarctica, the ozone layer that protects Earth from harmful solar radiation was disappearing.

"They did not know the extent of it because they only had data from one spot," said Pawan K. Bhartia, a NASA atmospheric scientist who was on the team analyzing NASA's Antarctic satellite data. The satellite readings also showed ozone levels so low the team thought it might be instrumental error. A few months after the British Antarctic Survey's paper, the NASA team presented findings at an atmospheric sciences conference in Prague that confirmed the ozone hole was real.

"After that," Bhartia said, "all hell broke loose."

The British Antarctic Survey data was accurate but the issue was more widely recognized when satellite images revealed that the ozone depletion was not confined over Halley Bay, but was continental in size. The NASA paper released a satellite image that showed the size and magnitude of the damage and made the "ozone hole" a well-known environmental phenomena. Word of the ozone hole spread through news headlines like wildfire, as people began to realize the significance of a region in the stratosphere that most had never heard of before.

Without the ozone layer Earth would be very different. Earth's gaseous envelope, the atmosphere, is made up of layers. When present near the surface, ozone (an unstable molecule composed of three oxygen atoms) is a pollutant. But in the stratosphere, the atmospheric layer 6 to 30 miles (10 to 50 KM) above the surface, ozone absorbs Ultraviolet-B (UV-B) radiation from the sun, which can damage DNA and lead to skin cancer in humans.

"The evolution of life is tied to the evolution of ozone," Bhartia said. "Ozone is critical for the longtime survival of the species."

A Realization: Human Impact

"With ozone depletion, mankind has demonstrated the capability to alter the world's atmosphere," says Larry Flynn, a physical scientist at National Oceanic Atmospheric Administration (NOAA). "The world's nations realized that it was not a limitless expanse but that human activity could have large and important impacts on the atmosphere."

In 1985, the nations of the world recognized that CFCs were a threat to our ozone layer. In 1987, a treaty to regulate CFCs was ready for signatures from countries around the world. By 1989, 193 countries had signed the Montreal Protocol, which phased down the production of CFCs. In the United States, the Clean Air Act of 1990 mandated that NASA and NOAA monitor the ozone hole. By 2011, every nation in the world had signed the Montreal Protocol.

"Atmospheric ozone is no longer declining because concentrations of ozone-depleting chemicals stopped increasing and are now declining," says Flynn.

Future of Recovery

But the atmosphere does not have a straight line to recovery. The same chemistry that creates the Antarctic ozone hole also takes place in the Arctic. The Arctic stratosphere is not as cold and isolated as in the Antarctic, so ozone depletion does not usually reach the very low levels seen in the ozone hole. In the winter of 2011, ozone depletion in the Arctic was very large because of a colder than usual winter. Colder temperatures lead to increased presence of polar stratospheric clouds; ice crystals in these clouds speeds up chemical reactions that break down ozone.

Matt DeLand, chief research scientist for Science Systems and Applications, Inc., said satellite monitoring of the ozone layer has become increasingly important since budget cuts have scaled back ground-based monitoring in many places.

"We are seeing that while the overall ozone layer is getting better, we still see changes in the Arctic," DeLand said. "We shouldn't relax." While CFCs have been regulated, greenhouse gases continue to increase, and these gases may have unrecognized effects on our ozone layer.

Laura Betz
NASA's Goddard Space Flight Center, Greenbelt, Md.

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