Fall 2013 Breakthroughs

Author(s): Elizabeth Gardner
Photographs by: Kerri Pratt and provided

Sunlit snow triggers atmospheric cleaning, ozone depletion in the Arctic

Sunlit snow

Purdue graduate student Kyle Custard explores the snow-covered sea ice near Barrow, Alaska.

A Purdue-led team of researchers discovered sunlit snow to be the major source of atmospheric bromine in the Arctic, the key to unique chemical reactions that purge pollutants and destroy ozone.

The team’s findings suggest the rapidly changing Arctic climate –– where surface temperatures are rising three times faster than the global average –– could dramatically change its atmospheric chemistry, says Paul Shepson, the professor of chemistry who led the team.

“We are racing to understand exactly what happens in the Arctic and how it affects the planet because it is a delicate balance when it comes to an atmosphere that is hospitable to human life,” says Shepson, who also is a founding member of the Purdue Climate Change Research Center. “The composition of the atmosphere determines air temperatures, weather patterns and is responsible for chemical reactions that clean the air of pollutants.”

Changes in the Arctic are felt throughout the rest of the planet through weather changes, like the longer and colder winter the Midwest experienced this past year due to Arctic weather systems, he says.

“Although changes in the Arctic seem far removed from our daily lives, more than the polar bears will be affected by the rising temperatures and melting sea ice,” he says. “We need to know what is happening there now in order to understand what we may face in the future.”

While it was known that there is more atmospheric bromine in polar regions, the specific source of the natural gaseous bromine has remained in question for several decades, says Kerri Pratt, a National Science Foundation postdoctoral fellow in polar regions research at Purdue who participated in the research.

She and Purdue graduate student Kyle Custard performed the experiments in minus 50 to minus 30 degree Fahrenheit wind chills near Barrow, Alaska. The team examined first-year sea ice, salty icicles and snow and found that the source of the bromine gas was the top surface snow above both sea ice and tundra.

“Salts from the ocean and acids from a layer of smog called Arctic haze meet on the frozen surface of the snow, and this unique chemistry occurs,” Pratt says. “It is the interface of the snow and atmosphere that is the key.”

A paper detailing the results of the National Science Foundation and NASA-funded work is published online at Nature Geoscience.

New visualization reveals virus particles have more individuality than thought

Virus particles of the same type had been thought to have identical structures, but a new visualization technique developed by a Purdue researcher reveals otherwise.

The bacteriophage T7 procapsid structure and
the DNA packaging apparatus at the portal
vertex was reconstructed using single particle
cryo-EM and a new Focused Asymmetric
Reconstruction (FAR) image processing technique
developed by Wen Jiang, a Purdue associate
professor of biological sciences.

Wen Jiang, an associate professor of biological sciences, found that an important viral substructure consisted of a collection of components that could be assembled in different ways, creating differences from particle to particle.

“There are actually slight differences that result in a number of potential structural combinations for this part of the virus,” Jiang says. “By looking at only one very small part of this substructure at a time, we were able to obtain clear images and show various different combinations an individual particle could possess. Better visualization allows us to better understand the structure of viruses, which could lead to new ways to treat infections and improve human health.”

In his pursuit of improved imaging, Jiang studied the bacteriophage T7, a virus that infects bacteria. He focused on a small substructure, called the portal vertex, to see if it was identical across individual particles. The portal vertex is similar to a stack of five rings, where each ring is made of several copies of a single protein molecule that is different for each ring, he said.

He found that when he focused only on one pair of neighboring rings at a time, the computer analysis and averaging worked, and a clear image was obtained. When he tried to include three or more rings, the images were smeared.

Jiang named the new imaging method “focused asymmetric reconstruction,” or FAR, because it focuses in on a single neighboring pair of components. A paper detailing the technique and findings of the National Institutes of Health-funded research was published in the journal of the Proceedings of the National Academy of Sciences.

Purdue professor wins the Hamburg Prize for Theoretical Physics

A Purdue University professor has won the 2013 Hamburg Prize for Theoretical Physics for his work on “giant” molecules.

Chris Greene, a distinguished professor of physics, won the prize for his theory of an unusual binding mechanism in ultracold quantum gases and the existence of huge Rydberg molecules, electronically excited molecules that behave in unique ways and can exhibit exaggerated sizes. His prediction, published in 2000 with coauthors Alan Dickinson and Hossein Sadeghpour, helped to trigger the experimental discovery of these unusual Rydberg molecules in 2008.

The prize, which is jointly awarded by Joachim Herz Stifung and the Hamburg Centre for Ultrafast Imaging (CUI), includes $53,444 and a research and teaching visit at the University of Hamburg. Greene received the award Nov. 14 during the annual CUI-Colloquium on the Science Campus Bahrenfeld in Hamburg.

“In being awarded the Hamburg Prize for Theoretical Physics, Chris joins a very elite group of physicists who have made fundamental contributions to our understanding of quantum systems,” says
Andrew Hirsch, interim head of the Purdue Department of Physics. “His work in the field of atomic, molecular and optical physics places him at the very forefront of an area of physics that holds both great discovery and application potential.”