From the Philadelphia Inquirer:

------------------------------------------------------------------------Posted on Fri, Mar. 28, 2003
Why Iraqi sandstorms are orange
By Tom Avril
Inquirer Staff Writer

Why do the sandstorms in Iraq appear orange?

Two reasons.

First, the sand and dust themselves have an orangeish hue for much the same reason that the surface of Mars appears reddish-orange.

The color comes from iron oxides - essentially, rust - that result from "the weathering of common rocks," said Ronald Greeley, professor of geological sciences at Arizona State University.

Second, when the sand and dust are kicked up into the air by wind, the color is intensified, said Yoram Kaufman, an atmospheric scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

Ordinarily, an orange object looks orange because it reflects orange light and absorbs the other colors in the spectrum.

When millions of dust particles are suspended in the air, light is bounced around between them repeatedly before it reaches the human eye. Each time the light strikes a dust particle, more of the blues and other non-orange colors get absorbed, Kaufman said. So by the time the light reaches us, all that's left to see is the orange.

"Instead of absorbing only once," Kaufman said, "the blue is absorbed even more."
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Contact staff writer Tom Avril at 215-854-2430 or tavril@phillynews.com.
http://www.philly.com/mld/philly/news/nation/5499589.htm

Bob Clark