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Chemist finds current climate change models should bite the dust |
| Joseph Caputo |
The Sahara Desert is a shedder. No matter what the season, it releases a plague of unwanted grains into the atmosphere that eventually ride the wind across the Atlantic Ocean. Throughout their journey, the approximately 100 million tons of vibrating soil and sand granules bounce against ozone precursors, pollutants, and each other. By the end of the flight, reactions between the solid particles and atmospheric gases have formed new molecules, products with mysterious consequences for climate change.
In computer-generated models of possible factors contributing to global warming, the net effects of mineral dust on the Earth's climate are still unknown. Particulate matter from deserts and dirt scattered over the planet are often lumped together as one in atmospheric models, keeping their overall role and sources vague. A growing number of chemists, however, are arguing that dust from specific sites reacts with local atmospheres in vastly different ways. Their mantra: "Mineralogy matters."
One such scientific revolutionary is Ryan Hinrichs, a professor of chemistry at Sarah Lawrence College. "If dust originates in the Sahara, the actual minerals may be different than if it originated from the Gobi desert," he believes. "How is that going to affect the chemistry over the Atlantic versus the Pacific?"
Hinrichs set out to solve the mineralogy dilemma by comparing the molecular products of the atmosphere's interaction with two aerosol clays that differ slightly in three-dimensional shape. To find differences, he uses infrared spectroscopy to scatter light off of the airborne particles. The spectrometer detects reactions with the atmosphere and makes graphical records called spectra. These are read by scientists as molecular fingerprints to identify product chemicals.
After three years of research on a National Science Foundation grant, Hinrichs and his student assistants will publish "Heterogenous Reactions of Gaseous HNO3 [nitric acid] and NO2 [nitrogen dioxide] on the Clay Minerals Kaolinite and Pyrophyllite," in the Journal of Physical Chemistry A. The title defines the line of experiments throughout the paper, in this case the reactions of two prevalent atmospheric gas pollutants on solid airborne particles.
Megan Angelini, a senior and lead author of the paper, was responsible for setting up procedures, preparing samples, running tests and analyzing the majority of the data. "It's kind of weird doing research," she says. "You often think of experiments like in a science class, where everything is all set up for you. We had to really think about what questions we were asking and figure out appropriate techniques."
"Real research is troubleshooting and problem solving," says Professor Hinrichs. "These experiments haven't been done before." While pioneering work lessens the pressure to publish in a competitive field, it also means large investments in time. "There's a lot of waiting around in research," wrote co-author Sarah Rosen, a former S.L.C. student who transferred to Barnard College. "We occasionally spent entire days running one or two reactions. I maintained interest by thinking in terms of the big picture--about the potential application for our work to the world in which we live."
According to Hinrichs, this research is significant because human actions may be increasing the amount of mineral dust in the atmosphere. This would affect climate by reacting with ozone precursors to reduce ozone in the atmosphere. It could also cool the Earth by scattering solar radiation or contribute to warming by absorbing and readmitting outgoing radiation.
After evaluating the spectra, the research team found that when reacting with the atmosphere, kaolinite and pyrophyllite do form different products, providing solid evidence that mineralogy does matter. Hinrichs hopes that others will appreciate that computer simulation needs to include different mineral components in their models. "They can't treat it all as one because it is an oversimplification of reality," he says.
V
Professor Hinrichs will leave S.L.C. in August to teach chemistry at Drew University. Although he will continue his research throughout the summer, his devoted colleagues and students at the Science Center face a huge loss. "He had faith in me," said Angelini. "He didn't treat me like I didn't know anything. It really meant a lot, especially as an undergraduate woman in science. You wouldn't get that elsewhere."
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