Photo courtesy of Pacific Northwest National Laboratory
The high-resolution sum frequency generation spectrometer developed by EMSL's Hongfei Wang serves as a resource for scientists studying iron oxides and aerosol particles.
Even after the holiday hustle and bustle, Amanda Mifflin can smell Christmas in the air – and in, of all places, a research lab at EMSL. That's because she's studying alpha-pinene, an organic compound emitted from trees – such as pine trees – that gives off a pleasant odor.
"Normally chemicals we use in our studies don't smell good," said Mifflin. "But with this, it smells like Christmas."
But scientists question if alpha-pinene's impact is less than pleasant. Studies at EMSL may help answer that question. EMSL, or the Environmental Molecular Sciences Laboratory, is a Department of Energy national scientific user facility within Pacific Northwest National Laboratory (PNNL) supported by the DOE Office of Science.
Alpha-pinene (α-pinene) is a terpene, one of the organic compounds emitted by plants and trees that are important in biology for cell signaling and species communication. When released into the atmosphere, these small volatile molecules are oxidized by ozone and hydroxide, and their products form particles that affect air quality and climate.
Scientists, including Mifflin, want to understand the conditions under which these transformations occur and then quantify their impact on air quality and climate in hopes of improving global climate models. The problem is not insignificant. The ecosystems in which these compounds appear stretch across 10 time zones, in some cases.
Mifflin began studying α-pinene at EMSL while on sabbatical from her role as an assistant professor of chemistry at the University of Puget Sound in 2012. At EMSL, she has conducted a series of studies in collaboration with EMSL chief scientist Hongfei Wang and Franz Geiger, a professor at Northwestern University and her former graduate advisor.
At the center of her efforts is a new high-resolution sum frequency generation (SFG) spectrometer Wang and postdoc Dr. Luis Velarde developed that improves the resolution that can be achieved by more than 10 times over previous systems. Greater resolution provides greater levels of detail about complex particle structure and reactions on surfaces. With α-pinene, Mifflin and Geiger wanted to understand the structural properties and how they might change under different conditions.
Beauty of peaks
The data obtained with Wang's new system "are beautiful," Mifflin says. Past techniques provide data that, when graphed, look like rolling ‘hills.' With such wide hills (or broad data peaks), it leaves lots of room for interpretation and, as Mifflin says, "scientists are arguing about how to interpret the meaning." With HR-SFG, however, those rolling hills become jagged peaks – as many as a dozen in the same space as the wide hills - that provide much more specific data and, therefore, meaning.
Photo courtesy of Pacific Northwest National Laboratory
EMSL Scientist Hongfei Wang (right) and collaborator Amanda Mifflin work on the high-resolution sum frequency generation spectrometer prior to running experiments.
The data clearly showed more structure than had ever been achieved before in studying this complex molecule and how it interacts with surfaces.
"This technique is in fact giving us new information that will be really helpful," Mifflin says. "When we first saw the peaks, it was a beautiful spectrum."
What the newly resolved peaks and valleys mean will be addressed in studies through a collaboration with Geiger, Regan Thomson of Northwestern University, Scot Martin of Harvard University and Victor Batista of Yale University. The next phase will be using HR-SFG to study samples that are grown in Martin's laboratory and that are from a research site in the Hyytiälä forest of conifer trees in Southern Finland known for its long, dry and cold winters and its short but pleasant summers.
Geiger values collaborations across multiple institutions, including EMSL, and says Wang's "machine is just wonderful. It's really a terrific method."
This method is the gift that keeps on giving. Mifflin also has studied iron oxides, a complex mineral oxide, using HR-SFG. Iron oxides are much tougher to analyze than commonly studied oxides like silica. She'll be looking at how organic ligands bind to iron oxides and then capture a geochemical perspective of metal transport in groundwater.
The interactions of organics and mineral surfaces are poorly understood even though they can be important in the transport of contaminants in groundwater and the subsurface.
Mifflin appreciates that the HR-SFG allows her to study a variety of scientific challenges all related to environmental issues, from air pollution to carbon cycling and climate. And she recognizes that with EMSL, she can pursue these passions in many forms.
"I'm a physical chemist by training but it's the environment that keeps me interested. The direct tie of my work to environmental chemistry is a big draw for me."
The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit
. Mifflin spent her seven-month sabbatical at EMSL located at Pacific Northwest National Laboratory through PNNL's Alternate Sponsored Fellow program. For more information about PNNL's Alternate Sponsored Fellow program, please visit the web
. For more information is available on the HR SFG
Staci West is the communications manager for EMSL at PNNL