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EACH CRYSTAL-CLEAR RAINDROP has dirt at its core. Tiny air- borne mineral particles—desert sand, topsoil dust, volcano ash, man-made soot—get layered with moisture from the air until droplets form and fall as rain. For ocean-dwelling micro - organisms, rain is a crucial source of iron. An influx of iron particles raining into the sea can stimulate plankton blooms, and since plankton take up carbon dioxide they help reduce global warming. But before then, while particles remain in the atmosphere, sunlight can alter their chemistry and pro- duce pollutants that increase global warming. “It’s a very complicated story,” says chemist Juan Navea. “Our lab is fine-tuning the data used by major atmosphere and climate- modeling systems.” Daniel Lesko ’17 and Amanda Paskavitz ’17 (at left), Navea


(center), and Jaya Borgatta ’16 and Matthew Lueckheide ’17 (at right) worked on several aspects of aerosol particle dissolu- tion, adsorption, and photochemistry. Using power-plant fly ash from coal mined in the US, Central Europe, and India,


the researchers tested how long it takes the particles to dis- solve; such aerosols typically float in the air, carried on wind currents all around the world, for weeks and even months. They also analyzed how the interactions between atmos - pheric compounds and dust particles are affected by sunlight. Exposing the particles to ultraviolet light in a solar simulator, they could check and recheck the chemistry every few min- utes, and “we may see that the compound attached to the particle lessens over, say, 30 minutes,” Navea says. “Where do those compounds go? They get released as greenhouse gases —such as nitrous oxide, which is 300 times more powerful than carbon dioxide as an agent of climate change.” The researchers used spectroscopy to identify chemicals, but there are no instructions or lab books for analyzing the varying shapes of these layered, agglomerated molecules. To confirm their findings, they compared spectroscopic results with quantum chemistry simulations on a computer. g


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