NSF grant funds IU scientist?s study of `the Pac-Man of the atmosphere?

  • Sept. 29, 2014


BLOOMINGTON, Ind. -- Indiana University scientist Phil Stevens has been awarded a three-year, $718,562 grant from the National Science Foundation to continue his study of the impact of emissions from forests and their relationship to climate change and pollution.

Stevens is the Rudy Professor and chair of the environmental science faculty in the School of Public and Environmental Affairs and an adjunct professor in the Department of Chemistry at IU Bloomington. The grant will support measurements and modeling of processes involving the hydroxyl radical, a key factor in atmospheric chemistry.

"The hydroxyl radical is the Pac-Man of the atmosphere," Stevens said. "It's good to have, because it removes pollutants and helps clean the air. However, some models suggest that with increasing temperatures from climate change, emissions from trees may increase and this may decrease the concentration of the radical -- which means the ability of the atmosphere to clean itself would be reduced."

The hydroxyl radical, or OH, controls the atmospheric lifetime of methane, alternative chlorofluorocarbons, carbon monoxide and many other trace gases important to air quality and climate change. It also initiates the chemistry leading to the formation of ground-level ozone and particulate matter, the primary components of photochemical smog.

That means understanding the chemistry of the hydroxyl radical is extremely important. But it is also challenging, because the radical is short-lived, occurs only in low concentrations and is difficult to measure. Stevens' research group is one of only a few that can make accurate OH measurements.

Previous studies, including research Stevens helped conduct in Mexico City and Los Angeles, have produced a reasonably good picture of OH chemistry in urban areas. But the chemistry in natural environments is less well understood. Trees and other vegetation produce biogenic compounds that react with the hydroxyl radical. The interactions are not well understood and previous measurements and modeling of the chemistry have produced disparate results.

Stevens said some models suggest forests serve as a "sink" for the OH radical -- that compounds generated by trees react with and destroy the radical, reducing its ability to cleanse the atmosphere of pollutants. But some measurements have suggested that isn't occurring, and that the hydroxyl radical is instead recycled in the process and continues to be effective.

"The question we're trying to answer is, are these tree emissions green or not green," Stevens said.

The grant will fund measurements of the hydroxyl radical and the hydroperoxyl radical, or HO2, at forested sites including the Indiana University Research and Teaching Preserve near Bloomington, the University of Michigan Biological Station in Northern Michigan and the Manitou Experimental Forest Observatory in Colorado. Stevens and IU graduate students will carry out the research in collaboration with scientists from other institutions.

To speak with Stevens, contact Steve Hinnefeld at 812-856-3488 or slhinnef@iu.edu, or Jim Hanchett at 812-856-5490 or jimhanch@indiana.edu.

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Media Contacts

Steve Hinnefeld

Jim Hanchett

  • School of Public and Environmental Affairs
  • Office 812-856-5490
  • jimhanch@indiana.edu