CFC replacements: better but not ideal.

CFC replacements: Better but not ideal

The 1985 discovery of an ozone "hole" over Antarctica awakened the world to the dangers of chlorofluorocarbons (CFCs) after decades of their widespread use. Today, as companies fashion replacements for CFCs, scientists want to ensure the environmental safety of the new compounds before they build up in the atmosphere.

The first broad study of CFC substitutes shows that they should indeed cause less damage to Earth's ozone layer and contribute less to the greenhouse effect than the CFCs. But the new analyses, based on computer models of the atmosphere, also reveal that the substitutes are far from harmless.

"They're to be used with some precautions. They don't answer all the concerns we have," says Donald A. Fisher, an atmospheric scientist at Du Pont in Wilmington, Del., the world's largest producer of CFCs. With colleagues from several U.S. and Norwegian research institutions, he describes the study's results in the April 5 NATURE.

CFCs harm the protective ozone layer because their long atmospheric life spans allow them to drift up to the stratosphere, where ultraviolet light breaks them apart and frees ozone-destroying chlorine. In addition, CFCs contribute to greenhouse warming by absorbing infrared radiation emitted by the Earth.

Their replacements address the ozone problem in two ways (SN: 4/9/88, p. 234). Some lack chlorine altogether, while others include a hydrogen atom that presumably shortens their atmospheric life span, preventing them from reaching the stratosphere in large amounts.

The atmospheric models verify that assumption, showing that the chlorine-containing replacements have less than 10 percent the ozone-destroying potential of CFCs. But the same models indicate that these compounds, while an improvement over CFCs, can still harm stratospheric ozone, whereas those without chlorine cannot.

And both kinds can add to the greenhouse effect, the computer models show. Though many of the substitutes are better than CFCs by a factor of 10 or more, they would still exert a strong warming effect on Earth's climate if allowed to build up.

Fisher says the modeling results underscore the need to view this first generation of replacements as an intermediate measure to help wean the world from CFCs as quickly as possible.