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.
At the AGU meeting in 1997, Jaffe presented computer modeling indicating the likelihood that, under the proper springtime conditions, air pollution from East Asia could make its way across the Pacific relatively undiluted within a matter of days. Data collected from the UW's Cheeka Peak Observatory on Washington's northwest coast in 1997 and 1998 confirmed the model's prediction, though that data did not indicate heightened ozone levels.
To gather this year's data, Jaffe's team used a University of Wyoming plane that is part of a fleet of research aircraft operated by the National Science Foundation. The plane was outfitted with essentially the same equipment used at Cheeka Peak. On 14 flights between March 15 and April 28, the plane gathered data from several equally spaced levels between 1,500 feet (the same elevation as Cheeka Peak) and 23,000 feet. Pollution layers were observed on about one-third of the flights.
"This was a day when we could really see haze layers out there," Jaffe said of the April 9 flight.
Other scientists involved in the research are from the UW, Seattle; the University of California, Irvine; the National Oceanic and Atmospheric Administration; and the Atmospheric Environment Service of Canada.
Jaffe's previous research has shown that Asian pollution travels to North America when meteorological conditions over the Pacific are just right, typically during the spring. A low-pressure system over the Aleutian Islands and a high-pressure cell near Hawaii, which remain stable and in place for at least several days, work in concert to quickly move air from East Asia directly across the ocean to North America. The process, which the researchers have dubbed "The Asian Express," takes four to 10 days, too little time for the air to be cleansed over the ocean.
"For us to see what we're seeing, I think we have to be talking about a fairly large region of pollutants that remain intact and get transported across in one big blob," Jaffe said.
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