Study: Bark beetle may impact air quality, climate

by Tim Crosby

CARBONDALE, Ill. -- If you’ve traveled to a forested national park out West in recent years, you may have noticed two things. First, a growing number of lodgepole pine trees are dying, victims of the bark beetle. And secondly, atmospheric haze, caused in part by tiny solid particles suspended in the air, is becoming a problem.

A study by a researcher at Southern Illinois University Carbondale shows these two phenomena may be related, tied together by chemistry and climate change factors.

Kara Huff Hartz, assistant professor of chemistry and biochemistry in the College of Science, has authored a study appearing today (May 23) in the journal Environmental Science & Technology, a division of the American Chemical Society. The study, which Huff Hartz conducted by collecting gas specimens from bark beetle-infested and non-infested lodgepole pines, shows a large increase in the gases given off by the beetle infestations, which could enhance airborne particulate matter problems and haze in the area.

The findings will bring better understanding to atmospheric maladies such as particulate matter, which can cause health problems in the very young and old, as well as other problems. It also may provide a window into understanding the links between climate change and environmental inputs such as volatile organic compounds (VOCs), which come from both natural and anthropogenic sources.

“I’m interested in gases that produce particulate matter as it contributes to climate change and that are also a health hazard,” Hartz said. “I look at how new particulate matter is formed and what its sources are. We know of a lot of sources, but when it comes to modeling how much is in the atmosphere we find that we can’t predict that very well, probably because we don’t know all the chemistry in the atmosphere.

“To me, this study looked at a potential source of particulate matter we didn’t think of before,” she said. “So if we can characterize it, maybe we can contribute to a better understanding of how much particulate matter is being formed in the atmosphere.”

Airborne particulate matter is a well-known health hazard that involves solids smaller in diameter than a human hair suspended in the atmosphere where they can be inhaled. Depending on the type, concentration and location, particulate matter can also impact climate by causing haze, preventing rain or leading to cooling, Huff Hartz said.

The gases given off by human activity and naturally occurring activity can enhance particulate matter concentrations in local areas, Huff Hartz said. This involves complex chemical and physical processes.

Anthropogenic VOCs -- that is, those caused by human activity -- arise from many sources, including burning fossil fuels. The presence of those VOCs increases the levels of atmospheric oxidants. When these human-caused oxidants mix with VOCs from both the human-caused and natural VOCs, the resulting oxidation can enhance existing particulate matter and can even form new particulate matter.

“If it was just the biogenic VOCs and along with very little oxidants we wouldn’t have this issue. It’s the enhancement that happens that we’re concerned about,” Huff Hartz said. “They form a product that is less volatile than it was before, and it can condense onto existing particulate matter, making it larger, or can even make more of it.”

Funded by almost $97,000 from the National Science Foundation, Huff Hartz’ findings come after her colleagues spent three months gathering samples from a dozen trees in a forested area near Steamboat Springs, Colo., in the fall of 2009. During that period of time, the fellow researchers extracted 400 air samples from trees using a handheld, battery-powered vacuum pump attached to a piece of tubing filled with a polymer sorbent material.

The polymer material adsorbed the VOCs while letting the other parts of the sample through. Those researchers sent the samples to Huff Hartz at SIU Carbondale, where she removed the VOCs from the sorbent material with a solvent, and analyzed them using gas chromatography/mass spectroscopy.

The samples from bark beetle-infested lodgepole pine trees suggested a 5- to 20-fold enhancement in total VOCs emissions. They also indicated the increased presence of beta-phellandrene emissions correlated with bark beetle infestation. Beta-phellandrene is a volatile organic compound.

Huff Hartz said the beta-phellandrene finding was quite unexpected and she intends to do further research with the substance in a laboratory at SIU Carbondale to see how it affects particulate matter enhancement and creation.

Huff Hartz said researchers don’t yet know why bark beetle-infested trees give off increased levels of VOCs. It could be caused by the beetle opening the tree trunk at a spot where it normally would be closed and allowing the VOCs to escape. Or it could be caused by a biosynthetic reaction between the tree and fungi that the beetles carry with them on their bodies.

“So it may be a multi-step process,” Huff Hartz said.

Huff Hartz said climate change has increased the bark beetle’s range in recent years, allowing it to spread to places it might not have in the past. Still, she said researchers have a lot of work ahead unlocking the relationships among the infestations, VOC emissions, particulate matter and climate change.

“If climate change is anthropogenic driven, is this really natural? It’s an intriguing question,” she said.

The journal article is titled “Effect of Bark Beetle Infestation on Secondary Organic Aerosol Precursor Emissions. It can be found at http://pubs.acs.org/doi/abs/10.1021/es204205m.