An aerosol haze blurs the Chicago skyline that is usually visible from Lake Shore Drive.

Aerosols may travel halfway around world

Even if you live on an Illinois farm, the air you breathe could carry pollution from Los Angeles. New models of atmospheric chemistry developed at Argonne are substantially altering our concepts of airborne pollutants and their impacts on cardiopulmonary disease worldwide.

Aerosol pollution—particles from 0.1 to 1 micrometer (millionths of a meter) in diameter—is a major hazard to human health. Much aerosol pollution consists of particles emitted from factories and motor vehicles, particularly diesel trucks. “However, recent evidence suggests that a significant fraction of the fine aerosols are formed by chemical reactions in the atmosphere from gases emitted by the petrochemical industry, automobiles and vegetation,” said environmental chemist Paul Doskey.

“Years ago, we thought these particles didn’t travel very far,” said Jeff Gaffney, senior scientist in Argonne’s Environmental Research Division. “Now we are realizing that they have lives of 20 to 60 days, which means they can travel halfway around the Northern Hemisphere. To take just one example, researchers are seeing air pollution from China carried by prevailing winds all the way to Seattle.”

These aerosols are typically transported along with ozone and other pollutants during the summer months. High concentrations have turned up in rural areas such as the Atmospheric Boundary Layer Experiments site in southern Kansas where the Argonne group has sampled air quality.

“These observations are significant because they have been taken far outside urban centers,” Gaffney said.  “Some days, you get air with 100 parts per billion ozone flying across the prairie—and that level would be a bad ozone day for a major city.”

The findings run counter to assumptions incorporated into earlier atmospheric models, which viewed the atmosphere as a number of county-sized “air sheds,” each of which retained almost all of its locally produced pollutants. Gaffney, Doskey, meteorologist Rich Coulter, environmental chemist Nancy Marley and modeler V. Rao Kotamarthi are now trying to change these models of the atmosphere to reflect their observations.

“Air shed modeling needs to take long-range transport into account,” Gaffney said.  “At the very least, regional rather than local pollution control strategies are needed—we are getting more evidence of how the entire planet is connected.”

The high concentrations of ozone over rural areas suggest that the effects of urbanization could potentially cause regional increases in health effects, agricultural and forest damage and secondary aerosol production if left unchecked, according to Argonne researchers. 

“We need to devote more effort to studying how air quality problems affect human health,” Coulter said. “But we do know that prolonged exposure to low levels of pollution can be as hazardous as a single large dose and that the background levels of some pollutants are building in the atmosphere every day.”

The group is attempting to establish more closely the relationship between aerosol and ozone transport, as the two are often observed together. The investigators are also trying to define the conditions in which new aerosol particles are formed in the atmosphere.

The work is sponsored by the Department of Energy's Office of Science, Office of Biological and Environmental Research, Atmospheric Science Program.

For more information, please contact Dave Baurac.

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