The likely hood
Are you sure they aren't smoking reefer at ozonehole.com? <g>
This article is interesting. It appears the South Pole has a unique molecular structure.
Another Antarctic Atmosphere Surprise: Scientists Find Evidence of Highly Oxidizing Environment Over the South Pole
More than 15 years after the discovery of an ozone hole in the stratrosphere over the Antarctic, the remote continent is yielding another atmospheric surprise.
A team of researchers led by the Georgia Institute of Technology has found a surprisingly high level of an air-purifying chemical (or oxidizing agent) in the near-surface atmosphere over the South Pole. The finding has implications for interpreting historical global climate records stored in Antarctic ice cores.
The summertime 24-hour average value of the primary atmospheric oxidant -- known as the hydroxyl (OH) radical -- at the South Pole is higher than that estimated from OH measurements recorded at the equator. The researchers will report their findings this fall in the journal Geophysical Research Letters.
The OH radical is widely recognized as vital to scrubbing pollution and naturally occurring chemicals from the air throughout the globe; it prevents a buildup of toxic levels of these substances.
"What we now know is that the near-surface atmospheric zone called the mixed layer (from the surface upward to between 20 to 200 meters) is a highly oxidizing environment at the South Pole," says Doug Davis, one of the lead researchers and a professor in the Georgia Tech School of Earth and Atmospheric Sciences. "Equally exciting, we are beginning to see evidence that a lot of this oxidizing chemistry is also occurring down in the snowpack. Thus, once things get buried in the snow, there continues to be active chemistry -- including oxidation -- that could further modify chemical species before they are trapped in the ice in their final chemical forms."
This finding suggests that glacio-chemists -- who study climate change based on an analysis of trace chemicals trapped in polar ice -- have to be far more careful in their interpretation of Antarctic ice cores, says Davis, whose research team is funded by the National Science Foundation. Changes in some chemical species buried may continue for another five to 10 years after they are trapped in the snowpack. Davis expects that scientists will soon focus more attention on this topic.
"Snow release of nitric oxide, which leads to the formation of OH, can in principle occur anywhere globally where there are accumulations of nitrate ions in ice and there is also solar radiation," Davis says. "Other researchers have found evidence of this phenomenon in Summit, Greenland, and Alert, Canada. What makes the South Pole unique is that the levels of nitric oxide and other nitrogen oxides are nearly an order of magnitude higher than anywhere else.
"But any significant elevation of nitric oxide at any snow-covered location should result in an enhancement of OH," Davis adds. "And, anytime you are producing higher levels of OH, it means this chemistry is having some local or regional impact. The final global impact from this chemistry, however, is still unknown."
At the South Pole, researchers recorded OH radical levels over a 24-hour period; the average measurement was about 2 X 106 molecules per cubic centimeter of air several days during their December 1998 to January 1999 expedition and again from December 2000 to January 2001. These measurements are nearly an order of magnitude higher than what they originally expected to find based on their Antarctic coastal measurements of nitric oxide, Davis says.
To measure OH, the scientists used the selected-ion chemical-ionization mass spectrometer (SICIMS) technique, which in the early 1990s became the first sensitive method for measuring this radical. Georgia Tech Adjunct Professor Fred Eisele, the other lead researcher for this project, developed the SICIMS technique at Tech. Eisele is also a senior research associate at the National Center for Atmospheric Research in Boulder, Colo.
To measure nitric oxide (NO), researchers used the well-established chemiluminescence technique with modifications to improve its sensitivity by an order of magnitude. Nitric oxide, also a radical, is a byproduct of internal combustion engines. But Davis and his co-workers believe NO is formed at the South Pole when ultraviolet radiation interacts with nitrate ions. Scientists are not certain about the source of the nitrate, but it could originate from stratospheric denitrification processes and the long-range transport of nitric acid formed at low latitudes during electrical storms.
Although the factors that cause NO levels at the South Pole to exceed 550 parts per trillion by volume of air (pptv) are still under investigation, Davis believes the most important factor is the atmospheric mixing depth at the South Pole. This depth seems to be highly variable at the pole and is sometimes no more than 25 meters above the surface. The Davis team's latest results indicate large fluctuations in atmospheric levels of NO without major changes in NO levels within the snowpack.
Elevated levels of NO (20 to 550 pptv) in the near-surface atmosphere react with the hydroperoxyl radical -- a less reactive oxidizing agent than OH -- and are converted to OH and nitrogen dioxide. The latter reacts with OH to produce nitric acid, which can return to the snow, thus forming a closed cycle.
"It's not that this is new chemistry," Davis explains. "Most of the time in the background remote atmosphere where NO levels are typically less than 10 pptv, a large fraction of the hydroperoxyl radical reacts with itself and creates hydrogen peroxide, which is lost to the surface. But at the South Pole, in the presence of this large source of nitric oxide, the hydroperoxyl radical predominantly reacts with NO to generate the more reactive OH radical. Everybody tends to associate nitric oxide levels with combustion, thus the South Pole is one of the last places on earth that you might expect to find nitric oxide in such large concentrations."
Davis and his colleagues discovered the high NO and OH radical levels in their funded research project to study sulfur chemistry. The project, called ISCAT, for the Investigation of Sulfur Chemistry in the Antarctic Troposphere, began in 1994 with an expedition to Palmer Station on the Antarctic Palmer Peninsula. Specifically, the scientists are working to more fully understand the oxidation of dimethyl sulfide (DMS) under the cold conditions and high latitudes of Antarctica. This information will also help glacio-chemists better interpret sulfate and methane sulfonate concentrations incorporated into the continent's 400,000-year-old ice records, Davis says.
Sulfate is a chemical signature for both southern hemispheric volcanic activity and major fluctuations in phytoplankton populations in the Southern Ocean that surrounds Antarctica. Phytoplankton lead to the release of DMS from the ocean, part of which is oxidized by OH to sulfate. Methane sulfonate is formed only from DMS.
Antarctic ice cores have revealed clear evidence of major volcanic activity in the Southern Hemisphere, and together with methane sulfonate, evidence of glacial and interglacial periods in the earth's climate history. The level of DMS is a chemical indicator of biomass production in the Southern Ocean, which, in turn, reflects both water temperature and solar radiation, Davis explains. So a more comprehensive understanding of DMS chemistry around and on the Antarctic should provide valuable information in studying past climate changes, he adds.
Based on the results of the sulfur chemistry studies led by Eisele and former Georgia Tech Research Institute scientist Harald Berresheim at Palmer in 1994, Davis and his colleagues moved their ISCAT research to the South Pole. They expected to record significant atmospheric transport of sulfate and DMS from the coast to the pole, which is 10,000 feet above sea level.
"Well, our initial hypothesis was wrong, and we found out why when went to the South Pole," Davis explains. "There was very little unreacted DMS that reached the South Pole because of the very high levels of OH in the near-surface air at the South Pole -- and perhaps more importantly -- over the entire polar plateau."
Elevated NO maintains a highly oxidizing environment on the polar plateau 24 hours a day, Davis says. The OH radical oxidizes most of the DMS before it reaches the South Pole.
"The oxidizing environment at the South Pole is truly astounding," Davis says. "We didn't expect it. And, initially, it made no sense. Nobody had the foggiest notion what was going on…. It was like finding some distant planet's atmosphere plugged into Earth's atmosphere, but having it limited to only the Antarctic polar plateau."
The researchers hope to make more sense of their data as they analyze measurements from their 2000-01 trip during the next year. Already, Davis' colleague, Associate Professor Greg Huey, may have identified a new atmospheric nitrogen oxide species in the Antarctic troposphere. The research team hopes to return to Anarctica in 2003 to continue its study. Other institutions represented in the ISCAT team are the National Center for Atmospheric Research, New Mexico State University, the University of California at Irvine, Drexel University, the University of Minnesota, the University of New Hampshire and Arizona State University.
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