UCI Study Uncovers Unexpectedly High Air Pollutant Levels In Southwest States

F. Sherwood Rowland, Donald R. Blake and colleagues sampled ground-level hydrocarbon gases through a 1,000 mile-wide swath of the central and southwest regions of the United States in late 2001 and early 2002. They recorded levels of various hydrocarbons -- including methane, ethane, propane and butane -- in and around Oklahoma City that equaled or surpassed those in such high-smog cities as Los Angeles, Houston, New York and Chicago.

These hydrocarbons participate in the formation of ground-level ozone, a major component in smog that contributes to lung ailments in children. Study results appear in the Online Early Edition of the Proceedings of the National Academy of Science the week of Oct. 6, 2003. (www.pnas.org)

"Based on these findings, it appears that the U.S. is emitting four to six million tons more methane per year than previously estimated," said Rowland, a Nobel laureate in chemistry and one of the world's leading experts on global air pollution. "In fact, our study suggests that total hydrocarbon emissions are higher than stated in current estimates. This means the American air pollution problem has still another new, significant aspect."

In their study, Rowland and Blake recorded high pollution levels in Texas, Oklahoma and southwestern Kansas. These regional levels correlated with the locations of the oil and natural gas refineries concentrated in these areas. The UCI researchers then compared atmospheric hydrocarbon levels in Oklahoma City and a dozen other U.S. cities. They discovered that the air in and around the Oklahoma capital contained more than double the amounts of ethane, propane and butane than the air in more congested urban areas. They also found elevated amounts of methane -- a gas that in the past half century is regarded second only to carbon dioxide as a root cause of the greenhouse effect.

In addition, their samples revealed ample amounts of alkyl nitrates. These chemicals are byproducts of the atmospheric reactions involving hydrocarbons that lead to the formation of ozone, a major component of urban smog. The alkyl nitrates are reliable markers of ozone formation and were found at levels higher than in most urban environments.

"Our group found these higher hydrocarbon levels over the area incorporating the largest natural gas and oil reserves in the continental U.S.," Rowland said. "Similar studies of natural gas and oil regions in other countries would help better monitor global emission of greenhouse gases such as methane which contribute to air pollution and overall climate change."

In addition to this Oklahoma City study, Rowland and Blake have studied the air content in high-smog cities such as Mexico City; Karachi, Pakistan; Santiago, Chile; and other areas around the world to help local governments improve their air quality.

UCI chemists Aaron S. Katzenstein, Lambert A. Doezema and Isobel J. Simpson assisted Rowland and Blake on this study. It was funded by the National Institute for Global Environmental Change, a division of the U.S. Department of Energy.

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