Improving Carbon Measurements In Global Climate Studies

By knowing the effects of plants on the atmosphere, scientists will be better able to determine the amount of human-generated carbon dioxide (CO₂) injected into the atmosphere, according to Greg Carmichael, professor of chemical and biochemical engineering in the UI College of Engineering and co-director of the Center for Global and Regional Environmental Research (CGRER).

"This work demonstrates a technique to get a direct estimate of the photosynthetic uptake by plants over large regions," he said. "This is critical because in the carbon budget analysis we need to be able to quantify the various sources of carbon dioxide, especially the carbon dioxide from anthropogenic activities and the uptake of carbon dioxide by plants.

"Both are needed if we are to come up with better management strategies in reducing manmade emissions and in the case of plants increasing their carbon uptake," said Carmichael, who was named in September to a National Academy of Sciences (NAS) study on the significance of the international transport of air pollutants.

In addition to Carmichael, the paper's UI co-authors include lead author Elliott Campbell, who participated in the study while earning his doctoral degree at Iowa and who currently is assistant professor of engineering at the University of California, Merced; Tianfeng Chai, former postdoctoral student at CGRER and currently at the U.S. EPA Air Resources Lab, Research Triangle Park, N.C.; Marcelo Mena-Carrasco, former UI doctoral candidate and currently at the Department of Environmental Engineering, Universidad Andres Bello, Santiago, Chile, and the Molina Center for Energy and the Environment, MIT; Youhua Tang, formerly of CGRER and now at the National Oceanic and Atmospheric Administration/Scientific Applications International Corporation (NOAA/SAIC); Jerald Schnoor, professor of civil and environmental engineering and CGRER co-director; and Charles Stanier, assistant professor of chemical and biochemical engineering, and assistant research engineer at IIHR-Hydroscience and Engineering.

In the paper, Campbell and his colleagues show that measurements of carbonyl sulfide (COS), a naturally occurring atmospheric gas consumed by plants, can be related to plant uptake of carbon dioxide. The hope is that future work can exploit this relationship to reduce uncertainty in carbon dioxide fluxes. The paper tells how COS analysis may be used as a measurement-based photosynthesis tracer.

"We've always looked at the total change in CO₂, but now we can look for the influence of photosynthesis on this total change," remarked Campbell. "Our approach, based on the relation of carbonyl sulfide to photosynthesis, gives us this unique ability."

The researchers used a NASA aircraft and NASA/NOAA funding to gather and analyze airborne observations of COS and carbon dioxide concentrations during the growing season over North America with a 3-D atmospheric transport model. They note that the study likely will result in additional measurements of COS being added to current carbon networks.

They plan to continue their work and use data from the NOAA-supported Iowa Tall Tower atmospheric measurement site in West Branch, Iowa, some 10 miles from the UI campus.

This research was published November 13, 2008 in the journal Science.