But a team of Penn State meteorologists suggests that, depending on the location, other pollutants may actually be the limiting factors.

“Sulfate aerosols have a large effect on the lungs and on visibility,” says Ariel Stein, graduate student in meteorology. “They are also the main component in acid rain.” While acid rain episodes have decreased over the past decades, there are still episodes of very acidic rain in the Northeastern United States.

Stein and Dr. Dennis Lamb, professor of meteorology, looked at the variety of pollutants that figure into the formation of sulfate particles. These emissions include sulfur dioxide, nitrogen oxides and volatile organic compounds.

“We wanted to see how controlling the chemicals that oxidize sulfur dioxide affected creation of sulfate aerosols,” Stein told attendees last week at the spring meeting of the American Geophysical Union in Boston. “Simply controlling sulfur dioxide does not always reduce sulfate.”

The researchers found that the reactions involved are not linear and that reducing one component does not always reduce the target. They also realize that controlling a specific emission is not always possible.

Sulfur dioxide enters the atmosphere when power plants burn sulfur containing coal or oil. Nitrogen oxides come both from power plant emissions and from automobiles. A more difficult pollutant to control is volatile organic compounds, half of which are produced by automobiles, with the other half produced by nature.

“In general, in most urban areas, if you want to reduce sulfate, reducing volatile organic compounds is more effective than lowering nitrogen oxides,” says Stein. “In rural areas, the opposite seems true, that lowering nitrogen oxides reduces sulfates.”

The researchers warn that these generalizations do not always hold true and that it depends on the meteorology. Sometimes, lowering nitrogen oxides, because of the other chemical present in the atmosphere, will actually increase the formation of sulfate aerosols.

Stein and Lamb are looking for indicators that would identify atmosphere conditions when lowering volatile organic compounds would be the best choice and conditions when lowering nitrogen oxides would be the way to go.

“Part of the problem is that the Environmental Protection Agency regulates emission levels but leaves it up to local governments to enforce EPA regulation,” says the Penn State researcher. “Municipalities are trying to fix a problem that is really regional, not local.”

Emissions from areas such as the Ohio River valley blow over the Northeast, leading the researchers to believe that creating specific approaches for urban areas will not necessarily control the situation. They are, however, modeling the various pollutants and indicator chemicals to indicate when sulfate levels will be sensitive to changes in volatile organic compounds and when they will be sensitive to changes in nitrogen oxides. - By A'ndrea Elyse Messer

[Contact: Ariel Stein, A'ndrea Elyse Messer]

06-Jun-2001