A team of researchers from the University of Pittsburgh and the Electric Power Research Institute (EPRI) has developed a method that could identify the sources of nitrogen oxide (NOx) emissions.

Researchers collected emissions samples from several power plant stacks in the U.S. and developed a method for detecting the isotopic signatures of NOx emissions under different configurations. These isotopic signatures will be instrumental in helping to identify emission sources of air pollution across the nation.

NOx emissions are formed during the combustion of fossil fuels. They mix with organic gases in the atmosphere to form ozone and particulate matter, the main components of smog. These emissions eventually settle onto surfaces, and the deposited material, primarily nitrate, carries a measurable isotopic signature. Until now, scientists were unable to fully interpret these signatures because they lacked the "fingerprints" of various NOx emission sources.

The team developed a method of extracting NOx emission samples from the stacks of coal-fired power plants and measured their isotopic composition. Sampling took place at facilities with and without advanced NOx-reducing technologies. Researchers discovered that emissions from power plants using the advanced NOx controls had different proportions of the 15N atom in the NOx they emitted than the plants without the advanced technologies or from NOx emissions from other sources. Scientists will then be able to analyze deposition samples and better determine the sources contributing to the emissions.

"We've been mapping the isotopes of nitrogen oxide deposition products across the nation," said principal investigator Emily Elliott, assistant professor in the Kenneth P. Dietrich School of Arts and Sciences Department of Geology and Planetary Sciences at Pitt. "These 'isoscapes' can only be interpreted with fingerprint data like the isotopic signatures collected in this study."

Pitt's researchers modified existing EPA methods to collect NOx from power plant stacks. Once collected, the lab utilized bacteria to convert nitrate into a gaseous form for isotopic analysis. Previous analytical approaches were both time- and labor-intensive and precluded widespread characterization of environmental nitrate isotopes. The "Regional Stable Isotope Laboratory for Earth and Environmental Research" study directed by the Pitt lab is now using these methods to examine isoscapes of nitrogen in air, water, and across ecosystems.

These results, combined with additional information from other NOx sources, will allow scientists to look at rain samples and determine how much nitrogen comes from power plants stacks as opposed to how much comes from such other sources such as motor vehicles, lightning, or soil.

Funding for this study was provided by EPRI and the U.S. Department of Agriculture.

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