Fires set for slash-and-burn agriculture in Asia, Africa, Australia and South America generate so much smoke that South Pacific skies are sometimes as smoggy as Los Angeles, according to a research paper by Nobel laureate F. Sherwood Rowland.
Research flights in 1996 detected significant levels of smog, most it thousands of miles from pollution sources, said Donald Blake, a co-author of the study. Both scientists work at the University of California, Irvine.
Rowland was in Dallas Tuesday to present the paper at the national meeting of the American Chemical Society. He shared the 1995 Nobel Prize in chemistry for discovering important aspects of ozone depletion.
A thin layer of high-altitude ozone gas protects the earth from the sun's ultraviolet rays. Ozone at surface levels, however, seriously harms people's respiratory systems.
It is a chief component of the smog that makes Los Angeles air the dirtiest in America.
A team of scientists sponsored by NASA, including experts from the National Center for Atmospheric Research and the National Oceanographic and Atmospheric Administration, carried out the research, covering islands from the Galapagos to Fiji.
They traced the pollutants to massive agricultural burning from areas where farmers are clearing brush to plant crops and graze cattle.
On several occasions, ozone over the Pacific was measured at 130 parts per billion, a level deemed unhealthy by the U.S. government.
``It was a revelation to see how widespread the effects of the burning are across areas of the atmosphere previously thought to be pretty pristine,'' said Elliot Atlas, a scientist with the National Center for Atmospheric Research.
``What came as a surprise was the extent of it and the fact that it traveled for such great distances,'' Blake said. ``We would have thought it would have dispersed more than it did.''
No evidence was found indicating that the Pacific ozone came from industry or motor vehicles. The researchers found higher levels of smog over the ocean than near the burning, Blake said.
The implications for human health were unclear. The flights measured ozone levels two to five miles above the surface, not at ground level.
But ``what goes up tends to come down,'' Blake said. Higher ozone``eventually can mix in with ambient air that people breathe.''
The flights predated last year's fire season, one of the worst ever in large parts of south Asia because of droughts associated with El Nino. The research will resume in 1999.