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Acid Rain, Washington, D.C., 1981

Photo: Close-up of red and yellow raindrops

In this macro close-up, a bromophemol solution is dripped on raindrops found on a daisy petal to test their acidity. The solution is reddish and has turned one drop yellow. The rain is pH 3, the same as vinegar.

(Text adapted from and photo shot on assignment for, but not published in, "Acid Rain: How Great a Menace?" November 1981, National Geographic magazine)

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Photograph by Robert Sisson