A plume of pollution that crossed the Pacific Ocean from Asia earlier this year contained ozone at levels high enough to violate a new federal ozone standard.
"This is air that has health implications," said Daniel Jaffe, an atmospheric scientist at the University of Washington, Bothell, whose team of researchers discovered evidence of the high pollution content in data collected during a research flight off the Washington coast on April 9. He will present his findings Monday (Dec. 13) at the American Geophysical Union's fall meeting in San Francisco.
Equipment aboard the plane detected an ozone level of 85 parts per billion at about 20,000 feet. That would exceed a new U.S. Environmental Protection Agency standard of 80 parts per billion (or 0.08 parts per million). That standard, which was formulated in 1997 but is under legal challenge and has not yet taken effect, includes time limits for how long ozone levels can remain at or above 80 parts per billion. It would replace the current standard that allows concentrations of 120 parts per billion.
Eventually, air at 20,000 feet is likely to mix into the lower atmosphere, but it is uncertain where it might come to ground level and create a health risk, Jaffe said.
The research flight also found an ozone level of 72 parts per billion at about 10,000 feet, an altitude lower than the tops of many peaks in the Cascade Range. At that concentration, ozone is known to damage vegetation, he said.
A meteorological analysis of the plume shows it came from East Asia, though the exact source is unknown, he said. At the same time, elevated levels of other pollutants, including hydrocarbons, carbon monoxide and a key smog ingredient called PAN (peroxyacetylnitrate), proved that the ozone-rich air mass had not come from the upper atmosphere because those pollutants do not exist at high concentrations in the upper atmosphere.