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New system to verify urban CO2 cuts

by Adrian Bishop 14 May 2012
New system to verify urban CO2 cuts

CO2 image via Shutterstock

U.S. scientists have developed a new method of verifying urban reductions in carbon dioxide (CO2). Researchers from Harvard and the University of Utah say their computer simulation data from Salt Lake Valley identified differences in CO2 emissions of over 15%.

The system could be used to verify urban CO2 reductions if a global treaty is signed to lower carbon dioxide levels and reduce global warming.

The findings are being published online in the Proceedings of the National Academy of Sciences this week.

The proof-of-concept first step is a ground-based method, but by using satellite monitoring the accuracy rate may be increased. The panel of the National Academy of Sciences recommends five per cent accuracy.

Co-author Jim Ehleringer, a University of Utah professor of biology, says the aim of the research was to collect data on carbon dioxide in the atmosphere of an urban area to see if emissions patterns could be predicted.

"The ultimate use is to verify CO2 emissions in the event that the world's nations agree to a treaty to limit such emissions. The idea is can you combine concentration information - CO2 in the air near the ground - and weather patterns, which is wind blowing, and mathematically determine emissions based on that information."

Massachusetts atmospheric scientists Kathryn McKain and Steven Wofsy, from Harvard University and Thomas Nehrkorn and Janusz Eluszkiewicz from the Atmospheric and Environmental Research, Inc. worked on the study with Prof Ehleringer.

It is difficult to detect absolute levels of changes in carbon dioxide using the new method, but it is possible, says Prof Ehleringer.

The new system estimates that there are more carbon dioxide emissions than reported in earlier government surveys of industry, he says, due to under-reporting.

Prof Ehleringer started monitoring Salt Lake Valley's carbon dioxide levels 10 years ago, as part of a National Science Foundation-funded study in the Urban Airshed - part of the atmosphere that behaves coherently in the dispersal of emissions.

University of Utah biologist Jim Ehleringer

University of Utah biologist Jim Ehleringer; Credit: Lee J. Siegel, University of Utah

Six sites in Salt Lake Valley and another in nearby Snowbird ski resort monitor carbon dioxide levels. The data collected, which can be seen at, is extensive.

A computer simulation of carbon dioxide emissions in the area was created, which included projections from sites at the University of Utah, downtown Salt Lake City and Murray, Utah.

Weather forecasts were used to predict air and wind circulation and satellite images of the landscape were taken into account.

The emissions estimates were within 15 percent or more of the official figures and the team would like to increase the accuracy to within five per cent in future.

Cities are major producers of carbon dioxide, so could be vital in testing reduction claims in future.

Carbon dioxide levels on the ground rose at might when the air was calm, but fell in the morning as the sun rose and plants consumed carbon through photosynthesis.

The scientists say satellite measurements though a mile wide upright column of air is more accurate as they are not so affected by variations caused by smoking chimneys or stationary traffic.

However, the researchers say there are no satellites at present that are able to properly target urban areas for accurately measuring carbon dioxide levels.

The one study, in Germany, that accurately measured an urban area's carbon dioxide emissions was too costly for everyday use.

Professor Ehleringer's role in the research was finance by the U.S. Department of Energy. Other funding came from NASA and the National Science Foundation.

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