Diana Hsueh at the University of California, Irvine, and colleagues collected corn from nearly 70 locations in the United States and Canada. They found that the Ohio Valley and California had the most fossil-fuel-emitted carbon dioxide, while the Colorado region had the least.
This method of measuring carbon dioxide produced by burning fossil fuels, such as coal, oil, and natural gas, can help atmospheric scientists better understand where carbon dioxide, a greenhouse gas, is located and how it mixes and moves in the air. Plants, the researchers say, provide a cost-effective way to record average daytime conditions over several months, as they take in carbon dioxide gas during photosynthesis, and it becomes part of the plant tissue. Their report will be published 23 January in Geophysical Research Letters, a journal of the American Geophysical Union.
The scientists chose corn, because it is widely grown and, as an annual plant, all of its carbon is derived from a single growing season. They avoided pollution point sources, such as highways and power plants, to allow for mapping of regional patterns across various states and provinces. In the laboratory, they dried samples of corn leaves and husks and chemically converted them into graphite. They then analyzed the graphite in a mass spectrometer, which measured levels of radiocarbon, a rare isotope of carbon.
Carbon dioxide derived from fossil fuels contains no radiocarbon, so it is easily distinguishable from other sources. With measurements from the mass spectrometer, the scientists calculated overall levels of carbon dioxide produced by fossil fuels at the locations where the corn samples were collected.
The scientists had expected carbon dioxide from California and other western coastal states to drift eastward, but they found that the Rocky Mountains appeared to provide a barrier. Air in the Mountain West, including Colorado, Idaho, and New Mexico, had the lowest carbon dioxide, about 370 parts per million. Air in the Eastern United States, which includes Massachusetts, New Hampshire, and New York, contained an additional 2.7 parts per million of carbon dioxide from fossil fuel sources.
Air in Maryland, Ohio, Pennsylvania, and West Virginia had nearly twice as much additional carbon dioxide from fossil fuels, 4.3 parts per million.
"Many nations are facing increasing pressure to monitor and regulate the release of carbon dioxide from fossil fuel sources to limit greenhouse gas warming," said James Randerson, a co-author of the study. "This method can help determine how much fossil fuel carbon dioxide is coming from different regions."
"We have to better understand emission patterns and changes in the atmosphere in order to better regulate fossil fuels," said Susan Trumbore, another co-author of the study. "This is a direct way to measure the release of carbon dioxide emissions that are contributing to climate warming."
The research was funded by the National Science Foundation and NASA.
Peter Weiss | AGU
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