8 December 1998

Asian Smog Settles In California

Air pollution from eastern Asia is beginning to have measurable effects on air quality in western North America, a researcher from the University of Washington, said today.

Pollutants traceable to Asia include carbon monoxide, a direct byproduct of combustion; peroxyacetyl nitrate (PAN), indirectly caused by combustion; and particulates, said Dan Jaffe, an associate professor who studies atmospheric chemistry and air pollution.

Jaffe, meteorologist Theodore Anderson and several other researchers, are presenting their findings this week during the fall meeting of the American Geophysical Union.

The scientists found that Asian pollution travels to North America in the troposphere, at a maximum altitude of about 10 000 feet, when meteorological conditions are right. 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, act like twin gears pulling a high-speed conveyor belt laden with Asian air directly across the Pacific Ocean. On average the air reaches the West Coast in about seven days, but it can take as few as four and as many as ten.

"We're still talking about a relatively small part of the pollution, but with the rapid industrial growth taking place in Asia we expect that the impacts will increase," he said.

Measurements taken on March 29, 1997, at the Cheeka Peak Observatory on Washington's northwest coast showed pollutant levels elevated substantially from what is typically found in marine air that has been cleansed as it crosses the Pacific. Several other instances of direct airflow from Asia during March and April 1997 also showed higher levels of the pollutants. However, the March 29 measurements came from air that was most clearly traceable to a large area of eastern Asia. Those readings showed carbon monoxide levels 10 percent higher than normal marine air, a nearly 100 percent rise in PAN, and a 50 percent increase in particulates.

"In this suite of measurements, we don't yet have enough data to say it's coal burning in China or an oil source in Tokyo. But we're moving in that direction," Jaffe said.

Jaffe said the team has not seen significant ozone increases from Asia as expected, but he's not certain whether that is because of limited sampling or because the model needs to be adjusted.