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A new study by Purdue University and NASA confirms the efficiency of CFCs and HFCs in trapping radiation in the atmospheric window, a property that makes these gases stand out in their warming potential. The study warns also against their powerful cumulative effect over time, stressing the urgency to move away from compounds containing fluorine to fluorine-free solutions.

Purdue University and NASA investigated several chemicals, including chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), for the physical characteristics in order to assess which properties are most important in determining their efficiency. The results of this work appear in a special edition of the American Chemical Society's Journal of Physical Chemistry A, which was released on 12 November 2009.

Employing both results from experimental observations and from computer modeling, the researchers concluded that:

• Fluorine-containing compounds are the most effective global warming agents

• Fluorine-containing chemicals might have a powerful cumulative effect over time

Fluorine atoms the decisive factor in making effective global warming agents

“The compounds, which contain fluorine atoms, are far more efficient at blocking radiation in the atmospheric window’”, said Purdue Professor Joseph Francisco, who co-authored the study. The atmospheric window is the frequency in the infrared region through which radiation from Earth is released into space, helping to cool the planet. When that radiation is trapped instead of being released, a "greenhouse effect" results, warming the globe.

“The fluorine atoms that characterise the chemicals [such as HFCs and CFCs] are highly electro-negative and tend to pull electrons to themselves”, Francisco said. “This shift makes the molecules more efficient at absorbing radiation, which would normally bleed harmlessly into space”. As a result, the fluorine-containing compounds are the most effective global warming agents, the study concludes.

Fluorine-containing compounds might have a powerful cumulative effect

The compounds also persist longer than carbon dioxide and other major global warming agents, said Lee, chief of the Space Science and Astrobiology Division at NASA Ames Research Center. The concern is that, even if emitted into the atmosphere in lower quantities, the chemicals might have a powerful cumulative effect over time. Some of these chemicals don't break down for thousands of years.