NCAR scientists investigate air above Antarctica

Four scientists from the National Center for Atmospheric Research (NCAR) are studying the chemistry of sulfur and nitrogen in the air above Antarctica. The investigation will help them understand the continent’s chemical processes better, as well as refine scientists’ interpretations of ice cores, which provide information on past climates.

The expedition, which runs through January 4, is part of the Antarctic Tropospheric Chemistry Investigation (ANTCI), a four-year program funded by NCAR’s primary sponsor, the National Science Foundation. Along with NCAR, 10 universities and federal laboratories are participating in the investigation.

“The atmosphere of Antarctica is probably the least explored part of the lower atmosphere on the planet right now. This is the first time people have looked at any of these chemical processes in this environment,” says Lee Mauldin, a chemist from NCAR and one of the project’s co-investigators.

The scientists are studying sulfur to learn more about its oxidation processes, or how it reacts with oxygen. Natural sources of sulfur in the atmosphere include emissions from volcanoes and the oceans. In Antarctica sulfur is released into the air mainly in the form of dimethyl sulfide, a reduced form of sulfur. In the air over Antarctica, the dimethyl sulfide reacts with oxygen to form sulfates. The sulfates are eventually transferred from the air to snow and fall to the ground, where they become part of the snow pack. Scientists drill ice cores deep into the snow pack and measure their sulfate concentrations to determine past geophysical events such as volcanic eruptions, El Niño episodes, and climate change.

The scientists are also studying nitrogen chemistry because they’ve found evidence of high levels of atmospheric nitric oxide, a reactive form of nitrogen, at the South Pole. In most regions of the world, nitric oxide is considered a pollutant, but it occurs naturally at the Pole when the sun shines on nitrate in the snow and a photochemical reaction releases the nitric oxide into the air. Levels are nearly 10 times higher at the Pole than in other parts of Antarctica.

“Sunlight releasing the nitric oxide in the snow is a unique phenomenon that nobody has seen before at the Pole. These levels bring the oxidizing capacity at the South Pole on par with that observed in the tropics, a region where this capacity is expected to be high,” Mauldin says. “As to the source of the nitrate in the snow, we don’t know that yet,” he adds.

Mauldin says that one of the reasons it is important to understand sulfur and nitrogen processes in Antarctica is because they are natural phenomena happening in one of the more remote regions of the planet. “You need to understand background processes in order to differentiate them from anthropogenic [human-caused] processes when you look at more complicated areas,” he says.

Scientists will measure the chemicals from the ground at the South Pole and from the air in different locations above Antarctica. During the airborne component, they’ll fly from McMurdo Station on the coast in a Twin Otter aircraft with air-sampling instruments on board.

As part of ANTCI’s outreach component, a high school teacher from Rockdale County High School in Conyers, Georgia, is accompanying the scientists and will communicate with her students via an interactive Web site that is also available to the public. The teacher, Jill Beach, will help set up experiments, prepare instruments, and compile data, in addition to maintaining the Web site.

“Not only will it be helpful to have another set of hands, but Jill’s going to be able to provide a unique outlook to people back home,” Mauldin says.

The scientists will return to Antarctica to take more airborne measurements in 2005 or 2006.

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under primary sponsorship by the National Science Foundation. Opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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