Purple Haze
Jimi Hendrix played "Purple Haze"--but did he know the chemical composition?This is Sandra Tsing Loh with the Loh Down on Science and on haze. Every year, plants give off hundreds of millions of tons of a chemical called isoprene. It's eventually transformed into haze-producing aerosols. In fact, isoprenes are the reason the Smoky Mountains appear, well, smoky. Atmospheric chemist Paul Wennberg and colleagues at Caltech now understand the mechanism by which that happens. Turns out, when isoprene is released into the atmosphere, it's chewed on by sunlight and oxygen. That transforms it into a new class of chemicals called epoxides. [ee-POX-ides] These epoxides, says Wennberg, are nature's glue. Your store-bought epoxy doesn't turn into a glue until an acid is added. Similarly, tree-spawned epoxides don't get sticky until they bump into acidic particles in the atmosphere. Then they glom onto to those particles, turning them into bigger, light-scattering aerosols. And voila! Purple Haze. And if that too-technical explanation spoiled the mystery for you? 'Scuze me while I kiss the sky!
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