Looking for Clues, Above and Below: THE SKY DETECTIVE

Sometimes when she talks about her work, Azadeh Tabazadeh mischievously mentions talk-show host Rush Limbaugh, who famously asserted that volcanoes are the cause of ozone depletion. "He was only half right," she says with a laugh. For as Tabazadeh and her colleagues have shown, volcanic eruptions do speed up the rate of ozone depletion--but only because their emissions combine with industrial pollution to create a destructive cocktail. Volcanic chlorine, for example, is water soluble, so it is quickly removed by rain. The sulfurous compounds that volcanoes spew out are another matter. These rise high into the atmosphere to create chemically active clouds that in the presence of man-made chlorine dangerously accelerate the process of ozone destruction. Volcanoes, says Tabazadeh, are a problem for ozone all right, but only because of us.

This is the kind of insight that other scientists have come to expect of Tabazadeh. As a UCLA graduate student, Tabazadeh made observations about the composition of high- altitude clouds that provided clues enabling scientists to understand why ozone destruction over Antarctica is so much more severe than over the balmier Arctic.

Tabazadeh, 39, grew up in Tehran and became interested in science at age 7, when an uncle gave her a chemistry set as a present. When she was 17, chafing under the restrictions placed on women by Ayatullah Khomeini's regime, she fled Iran with her brother, followed by other family members. Currently on leave from NASA, she is a visiting professor at Stanford, where her husband Mark Jacobson is an associate professor of engineering. The two are collaborating on a project that's probing the likely atmospheric impact of a broad-scale switch from fossil fuels to hydrogen. The results, she hopes, will provide society with the information it needs to make rational decisions about global warming. --By J. Madeleine Nash