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Intent on better understanding Earth's atmosphere, Margaret Tolbert and her research group spent years with their heads in the clouds -- polar stratospheric clouds, that is.
A professor in the chemistry and biochemistry department, Tolbert has spent much of her career studying the chemistry and physics behind stratosphere ozone loss. In 2004, she was elected to the National Academy of Sciences for her work on polar stratospheric clouds and sulfuric acid aerosols and their implications for the Antarctic ozone hole.
Recently Tolbert, who is also a fellow of the Cooperative Institute for Research in Environmental Sciences, has been working on a fundamental study of cirrus clouds wispy, high-altitude clouds rich in ice crystals. "There is now evidence that cirrus clouds have been increasing in the troposhpere in recent years, and we are not sure why," she said. "out of something like 10,000 particles in the troposhere, only one will end up nucleating an ice particle. Our group is trying to determine the nature of that special particle, to understand if it is of natural or anthropogenic origin, and finally to determine the cause of increased cloudiness."
One possibility is that particles from aircraft exhaust may serve as the "seeds" for the condensation of water molecules in the troposhere, Tolbert said. She and her students are chronicling key chemical reactions that cause the seemingly innocuous aircraft contrails to grow into cirrus clouds that spread across the sky in huge cloud banks over the course of a single day, causing Earth's heat budget to waver on longer time scales.
"In order to understand the atmosphere, we need to understand the clouds," she said. We now see that cirrus clouds have a big impact on climate by cooling the earth during the day and heating it at night.
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