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Research on atmospheric particles helps scientists better understand regional climate

BOONE—The Southeastern U.S. has not experienced the same warming that has occurred across much of the world during the past century. Researchers and climate educators at Appalachian State University are conducting research to better understand why that is happening.

View larger imageThe familiar blue haze of the Blue Ridge Mountains is the result of aerosols, small particles in the atmosphere that result from both human activity and natural sources. Researchers at Appalachian State University are studying how the particles buffer the Southeastern U.S. from climate warming and contribute to the formation of precipitation in the region.

“We think that is due to the high aerosol loading in this region, which to some degree counteracts greenhouse warming,” explained Dr. Brett Taubman, an assistant professor of chemistry at Appalachian.

The research, published in the International Journal of Climatology December 2012 in November 2012, was a collaboration between geography, chemistry and physics professors at Appalachian, and the National Oceanic and Atmospheric Administration. It was conducted at the university’s atmospheric research facility, called AppalAIR, Appalachian Atmospheric Interdisciplinary Research.

“Our site is particularly valuable at getting a picture of the regional footprint in the Southeast,” Taubman said. “We are in the middle of the region and our sampling site is located about a kilometer above sea level. We also are in a site that’s pretty rural without a lot of pollution sources.”

Aerosols are tiny particles in the atmosphere that result from human activity, such as burning wood or fossil fuels, or from motor vehicle, incinerator or power plant emissions. Aerosols from natural sources include sea salt that becomes airborne, particles from sandstorms and volatile organic compounds emitted by plants, such as terpenes.

“As the amount and chemical composition of aerosols change in the area due to changing anthropogenic and biogenic emissions, how will that affect this area in the future and the warming associated with climate change,” Taubman said. “This is a first attempt to begin to understand those processes.”

“Atmospheric aerosols are one of the least understood facets in the body of climate change knowledge,” said Ginger M. Kelly, outreach coordinator of the NASA-funded Climate Action Network through Direct Observations and Outreach program. She was the lead author of the studies that looked at the amount of aerosols collected during a 16-month research period, how their microphysical properties impacted solar radiation and how those factors related to precipitation patterns in the Southern Appalachian Mountains.

“A lot of time when we talk about climate change, it’s in the context of carbon dioxide emissions. Areas that aren’t focused on are atmospheric aerosols and land use changes,” Kelly said. “This work shows a methodology that can be used to determine how aerosols are influencing earth’s climate system.”

Aerosols play a key role in the formation of precipitation – both rain and snow. Raindrops form from tiny specks of dust or airborne particles.

“Aerosols that result from human activity, such as soot particles or black carbon, tend to suppress precipitation because their texture and size prevents the raindrops from growing large enough to rain out,” Kelly explained.

The particles also are associated with climate forcing in the summer when the number of particles in the atmosphere is greatest. “A lot of that is due to emissions from trees, which together with manmade emissions produce aerosols that scatter solar radiation back into space, which has a cooling effect,” Taubman said. “We see a tremendous variability in the summer, when we have high loading that you can see as a haze in the atmosphere. And then we’ll go to the cleanest of background atmosphere. As a scientist, it’s great to be able to sample from both.”

The researchers’ next step will be to analyze the chemical composition of aerosols collected at the AppalAIR site. “That has the potential to be tremendously important information,” Taubman said. “Then you can say if you have a certain type of chemical composition you can expect a particular type of climate forcing. That’s information that could be applicable to other parts of the world.”

In addition to Kelly and Taubman, other authors of the study were Dr. L. Baker Perry, geography and planning; Dr. James P. Sherman, physics and astronomy; Dr. Peter T. Soulé, geography and planning and Patrick J. Sheridan, National Oceanic and Atmospheric Administration.