Researchers unlock key to regional haze in Yosemite Valley in 2002

December 10, 2002

SAN FRANCISCO, Calif. -- A researcher from the Lawrence Livermore National Laboratory and colleagues from Colorado State University on Tuesday will show that forest fires likely contributed to periods of regional haze in Yosemite National Park in 2002.

Graham Bench, an LLNL scientist, and researchers from Colorado State conducted a three-month survey of air quality in Yosemite. Their findings, discussed Tuesday during the 2002 fall meeting of the American Geophysical Union in San Francisco, demonstrate that organic aerosol concentrations in Yosemite National Park were significantly above the historical average in 2002.

The researchers conducted their study taking measurements of PM 2.5, (particulate matter; in this instance, the particulate matter is 2.5 micrometers or smaller in size) from July to September 2002 from a site atop Turtle Back Dome in Yosemite.

Sources of PM2.5 include fuel combustion from automobiles and diesel powered vehicles, power plants, wood burning, forest fires, industrial processes and agricultural practices.

"It became apparent during the course of the study that smoke transported from massive wildfires in the Western United States likely contributed to periods of haze in Yosemite this year," said Bench, who works at Livermore's Center for Accelerator Mass Spectrometry.

Using mass spectrometry, Bench analyzed the air samples to determine the fraction of biogenic and man-made carbon contributing to the PM 2.5. His findings show that biogenic carbon contents varied directly with the total carbon loading and for periods of the study contributed up to 90 percent of the total PM 2.5. The high concentration of organic carbon that contributed to periods of reduced visibility in Yosemite this summer likely came from forest fires in Oregon and Southern California during the sampling.

PM 2.5 particles are so small that they are able to penetrate to the deepest parts of the lungs. Studies have shown links between fine particulate matter and numerous respiratory problems. PM 2.5 also is a major source of visibility impairment in most parts of the United States.

These fine particles also have a great attraction to water, which results in acid rain. Acid rain affects all biological or man-made products and can have repercussions to human health.

The group will present its findings at 1:30 p.m. Tuesday in Moscone Center, Room 124.
Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.

DOE/Lawrence Livermore National Laboratory

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