Crystalline Structure of Carbon Dioxide Seen for the First Time

For the first time, scientists are able to see the crystalline structure of carbon dioxide--a view that could help them learn how the crystals cause the greenhouse effect.

According to William Wergin and colleagues with the Agricultural Research Service, carbon dioxide crystals are as small as 1/200,000 of an inch. The crystals generally appear as eight-sided structures called octahedrons, the scientists say.

Carbon dioxide ranks high--along with nitrous oxide and methane--as a greenhouse gas that contributes to global warming as it increases in concentration in the atmosphere. Scientists say knowing the crystalline structure may give them clues to the capacity of carbon dioxide gas to absorb and re-radiate energy, which is the behavior of greenhouse gas that makes it so troubling.

Plants take up carbon dioxide through photosynthesis. When they are harvested, the crop residue is incorporated into soil and becomes organic carbon. This gives farmers a chance to reduce atmospheric carbon dioxide by improving their management of agricultural systems to increase soil organic carbon. The spinoff benefits from increased soil organic carbon are reduced soil erosion and improved soil tilth- -an indicator of soil health.

No one has ever before seen the structure of carbon dioxide crystals because the crystals evaporate at temperatures higher than minus 210 degrees F. But at ARS' Nematology Laboratory in Beltsville, Md., the scientists used a special scanning electron microscope (SEM) to view the crystals. At one point in the SEM viewing process, the material under observation is cooled to minus 320 degrees F, making it possible to observe the structure of the crystals of solid carbon dioxide.

Scientific contact: William P. Wergin, ARS Nematology Laboratory, Beltsville Agricultural Research Center, Beltsville, Md., phone (301) 504-9027, fax (301) 504-8923, wwergin@ggpl.arsusda.gov.