The structure of the frosty flakes also fascinate ice chemists like Purdue University's Travis Knepp, a doctoral candidate in analytical chemistry who studies the basics of snowflake structure to gain more insight into the dynamics of ground-level, or "tropospheric," ozone depletion in the Arctic.
"A lot of chemistry occurs on ice surfaces," Knepp said. Knepp can "grow" snow crystals year-round on a string inside this chamber. The chamber's temperature ranges from 100-110 degrees Fahrenheit down to minus 50 degrees Fahrenheit.
Knepp, under the direction of Paul Shepson, professor and head of Purdue's Department of Chemistry, is studying snow crystals and why sharp transitions in shape occur at different temperatures. "On the surface of all ice is a very thin layer of liquid water," Knepp said. Whenever you slip, you're not slipping on ice, you're slipping on that thin layer of water."
This thin, or quasi-liquid, layer of water exists on the top and sides of a snow crystal. Between 14 and 27 degrees Fahrenheit, crystals look like tall, solid prisms or needles.
Snow crystals transition to other shapes, and sometimes even back and forth, as the temperature and humidity change.
"The bottom line is that the thickness or the presence of this really thin layer of water is what dictates the general shape that the snow crystal takes," Knepp said. "By altering the quasi-liquid layer's thickness, we changed the temperature at which the snow crystal changes shape.
This knowledge has application for Knepp and his colleagues in their ozone work.
Ground-level ozone is very important. Complex chemical reactions regularly take place on the snow's surface. These reactions, which involve the thin layer of water found on the surface of snow crystals, cause the release of certain chemicals that reduce ozone at ground level.
"How fast these reactions occur is partially limited by the snow crystals' surface area," Knepp said. "Snow crystals with more branching will have higher surface areas than non-branched snow crystals, which will allow the rate of reaction to increase."
"Understanding ice and snow is part of that."

http://www.sciencedaily.com/releases/2009/12/091207143353.htm