The Air That's Up There: Atmospheric Scientists Focus on Nature's Role. (Cover Story)

Article excerpt

The atmosphere is a tough laboratory. On a bench top, chemists can devise and carry out controlled experiments. But chemistry isn't so straightforward outdoors. Natural and humanmade chemicals from countless sources enter the air and react--again and again. Atmospheric scientists are continuously working to untangle the complicated interactions. It's often still unclear precisely what chemicals are present in the atmosphere, how they got there, what they're doing, or where they're going.

Complicating matters is nature--specifically, plants. Although the casual hiker doesn't see it, trees, underbrush, and even dead leaves can emit gases that mix with pollutants above a forest canopy and form new compounds. More than 20 years ago, President Ronald Reagan took much heat for blaming killer trees for pollution. But while tree emissions alone aren't responsible for killing anyone, they can react with humanmade compounds to make chemicals that further pollute the air or contribute to climate change.

In recent research, atmospheric scientists have been filling in holes in their basic knowledge about the ways that nature affects the chemistry of the atmosphere. The forest's gaseous influence doesn't stop at its boundaries--the reaction of naturally produced chemicals with humanmade pollutants can influence air quality far downwind. Moreover, many scientists say, human influences on the atmosphere can't be fully understood unless the natural influences, such as tree emissions, are carefully calculated.

The research is fundamental, but its implications could be wide-ranging. It could help scientists understand the fate of airborne chemicals. "Are they going to stay in the atmosphere and continue to react?" asks Chris Geron of the United States Environmental Protection Agency in Research Triangle Park, N.C. "Are they going to travel far? Are they going to form some other compound that will react under different light and temperature?"

Obtaining those answers, in turn, can drive decisions about how to regulate industrial and automobile emissions. The knowledge being gathered helps scientists improve their computer models of weather and pollution patterns.

"The more you understand about the chemistry," says Geron, "the more you can tune your models and understand what's going on in the atmosphere."

Such models already play various roles, from informing people of impending smog conditions to guiding multimillion-dollar decisions on how governments regulate industrial emissions. "There's definitely a multitude of questions and areas of research that we can work in to improve the models," Geron says.

MYSTERY GASES Detailed air analysis is necessary in both urban areas, where people typically think about smog, and forested regions. Although it might look pristine, forest air is often infiltrated by humanmade pollutants, such as nitrogen oxides from cars on nearby roads or distant power plants. When these pollutants mix with a variety of natural chemicals spewed by trees, they form new chemicals--including some that researchers haven't yet identified.

By discovering exactly which pollutants are in the air, scientists can better determine where chemicals will end up, what reactions created them, and how to prevent the pollutants from forming in the first place.

Air-analysis instruments generally available today can't simultaneously and sensitively identify all the individual nitrogen-containing chemicals. Recently, atmospheric scientist Ron Cohen and his colleagues at the University of California, Berkeley invented a new device that simultaneously measures concentrations of several classes of nitrogen-containing air pollutants.

Cohen's instrument, described in the March Journal of Geophysical Research-Atmospheres, takes advantage of the fact that various nitrogen-based compounds break down into nitrogen dioxide at different temperatures. …