NASA, Purdue research shows global warming's molecular mechanics

After examining more than a dozen human-generated chemicals, NASA and Purdue University researchers found that carbon dioxide and methane, cited most often as causes of climate change, have less greenhouse warming potential than fluorinated compounds.

A NASA and Purdue University research team reports that they have discovered a blueprint of the underlying molecular machinery of climate change and global warming. The team found that compounds which contain fluorine atoms, widely used industrially, are the most efficient radiation blockers of Earth's "atmospheric window, " the infrared region of the atmosphere where radiation is released into space, cooling the planet. The global warming "greenhouse effect" results when radiation is trapped by infrared absorbing and emitting chemicals within the lower atmosphere. NASA scientist Timothy Lee, lead author of the study with Purdue Professor Joseph Francisco and NASA postdoctoral fellow Partha Bera, characterized the fluorinated compounds as having the potential to quickly slam the atmospheric window shut, as opposed to gradually easing it shut like carbon dioxide. Francisco, whose research focuses on the chemistry of molecules in the atmosphere, stated that in their results, chemicals such as chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur and nitrogen fluorides stood out starkly in their warming potential because of their efficiency in blocking radiation release. Lee said that their team's study is the first to delineate how, on a molecular scale, the chemicals listed as warming agents by the Intergovernmental Panel on Climate Change contribute to climate change. This research provides a rational design basis for developing benign alternatives and testing new chemicals for their global warming capability before they go to market, Francisco said. The NASA-Purdue study analyzed results from experimental observations and from computer modeling, using supercomputers from Information Technology at Purdue (ITaP) and NASA. Fluorine atoms are highly electro-negative and tend to pull electrons to themselves, Francisco said, a shift that makes the molecules more efficient at absorbing radiation, which would otherwise bleed harmlessly into space. The study concludes that the fluorine-containing compounds are the most effective and critical global warming agents, though the concentration of carbon-dioxide in the atmosphere is much greater. CFC use waned after it was discovered that the chemicals contributed to the destruction of Earth's protective ozone layer, which absorbs dangerous ultraviolet radiation from the sun. But concentrations of other fluorinated compounds, such as HFCs and PFCs, are increasing steadily because they persist in the atmosphere longer, and are still widely in use in air conditioning and the manufacturing of electronics, appliances and carpets. The team's results appear in a special edition of the American Chemical Society's Journal of Physical Chemistry A, released Nov. 12.