It was a typical winter in Antarctica. Temperatures hovered somewhere below freezing and fierce winds relentlessly blew massive gusts of snow across the icy landscape. Despite the bitter cold, Susan Solomon was outside eagerly taking measurements to understand what air and ice particles were doing high in the sky. And what she was about to discover laid the scientific basis for what would become one of the central environmental stories of the late 20th century.

Disturbing news that a massive hole had suddenly appeared in the Earth's protective ozone layer—letting harmful ultraviolet radiation reach the Earth—shocked the scientific community in 1985. Less than a year later, Solomon, M.S. chemistry '79, Ph.D. '81, developed a novel theory: chlorine species derived from man-made chlorofluorocarbons (CFCs) were destroying the blanket of ozone high above the South Pole. Evidence gathered during two expeditions to Antarctica in 1986 and 1987 confirmed her theory.

When CFCs—substances that had been widely used as spray can propellants and refrigeration materials since the 1950s—are released into the air, they eventually rise to the stratosphere, the region between 6 and 30 miles above the Earth's surface. Reaction of CFCs with sunlight frees highly reactive chlorine compounds. Solomon, a senior scientist at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, hypothesized that a reaction involving chlorine compounds on the surfaces of polar clouds destroyed the ozone molecules: "That reaction doesn't happen in the gas phase, but it happens quite readily on surfaces, such as ice particles that form polar stratospheric clouds." And because Antarctica is the coldest place on Earth, more polar clouds form there than anywhere else on the planet.

Solomon's discovery blew the whistle on CFCs and resulted in substantial amendments of the Montreal Protocol, an unprecedented international agreement established in the mid-1980s to protect the ozone layer. CFCs were banned in the 1990s and their concentration in the atmosphere recently has started to decline. Scientists predict that the ozone layer eventually will make a full recovery, but there is still a long way to go, Solomon cautions.

"CFCs have lifetimes of 50-100 years, which allows them not only to reach the stratosphere in significant quantities but also to remain in the atmosphere long after emissions have stopped," she says.

Solomon's discoveries were recognized with numerous awards, including the 1999 National Medal of Science. She also was inducted into the Colorado Women's Hall of Fame this year. In 1994, the Solomon Glacier and Solomon Saddle were named in honor of her leadership in Antarctic research.

Recently, Solomon has shifted her focus to gases other than carbon dioxide that could contribute to global warming. She and her colleagues showed that perfluorinated chemicals, highly potent greenhouse gases emitted during some semiconductor manufacturing processes, can live for thousands of years.

"A molecule that can outlast the pyramids of Egypt might be one to think carefully about venting into the atmosphere," she says. "The question is not just what is or may be happening now, but if something does happen tomorrow, how long will we have to live with it?"