First-of-its Kind Rice Paddy Study to Determine Methane Levels

04/16/02    Portland, Ore.

Methane is the second most important atmospheric gas implicated in global warming (after carbon dioxide). Four of its main sources are attributed to human activities: cattle, landfills, urban areas and rice paddies.

The latter will be the focus of a novel experiment that may one day become the standard by which atmospheric scientists worldwide efficiently gather accurate, timely information about greenhouse gases over large areas.

A recent $435,000 grant from the U.S. Department of Energy to OHSU's OGI School of Science & Engineering and Portland State University will fund the one-of-a-kind experiment. Rei Rasmussen, Ph.D., professor of atmospheric chemistry in the Department of Environmental Science and Engineering at the OGI School of Science & Engineering, and Aslam Khalil, Ph.D., professor of physics at Portland State University, are co-investigators.

Rasmussen and Khalil have been studying methane levels in China's rice paddies for 17 years. In 1981, they were the first to report that methane was increasing in the atmosphere, and they later determined that atmospheric methane had doubled in 100 years.

This summer, the internationally respected team will employ a new method of measuring methane -- a string of 12 colorful, durable balloons, each approximately the diameter of two average-size refrigerators. Six balloons will form a curtain on the downwind side of the paddy and six will contain the upwind side, encompassing about 6.2 square miles in area.

Sophisticated sampling equipment will be strapped to each balloon. As air flows across the rice paddy, the equipment will measure the precise concentrations of methane entering and exiting through an undisturbed, large source area.

"We can then compare this data with measurements that we've taken in past years using conventional ground-based enclosure chambers," says Rasmussen, who maintains in a sea of canisters on OHSU's West Campus, the world's largest collection of air. "Such chambers are now the standard way of determining the rate of methane flux to the atmosphere."

The balloon-borne "open curtain" experiment is the first of its kind in the world. It may prove a highly efficient way for scientists to gather accurate, timely information about atmospheric gases and pollutants over a large area, say Rasmussen and Khalil.

For example, the chambers typically used to collect and measure methane are efficient because of their small size but don't provide the consistent information scientists need to extrapolate results reliably from one area to another, much less make estimates about regions, such as countries.

"The beauty of the balloon approach," says Khalil, formerly an OGI faculty member who often teams with Rasmussen for field work, "is that we can extend our measurements to a much larger area. A large chamber can measure about one square meter of air. With this experiment, we're able to radically increase the scale by about 50 million times."

Obtaining methane samples from a larger area also will help Rasmussen and Khalil quantitatively understand nitrous oxide (another harmful atmospheric gas) and the mechanisms that naturally cause it to increase in the air as methane decreases. Such an understanding is critical for policymakers looking to reduce greenhouse gases capable of causing global warming from rice agriculture.

The OGI School of Science & Engineering (formerly the Oregon Graduate Institute of Science & Technology) became one of four specialty schools of Oregon Health & Science University in 2001. OHSU's OGI School of Science and Engineering has 63 faculty and more than 200 full-time master's and Ph.D. students in five academic departments.

Portland State University's Physics Department includes Atmospheric Physics and Global Change Science as one of its major research areas. The inter-disciplinary program spans several departments and includes 6 faculty and about 20 graduate and undergraduate students.