From the Princeton Weekly Bulletin, December 15, 1997
Research on aerosol requires collecting air samples at various atmospheric levels
They won't fly low enough
By JoAnn Gutin
Chemical engineer Lynn Russell has only one complaint about the former military pilots who help her collect air pollution data for her research: they won't fly low enough. "The thing is," she says, "the information I'd really like to have would come from maybe 20 feet above the ocean surface. And they won't go any lower than 100 feet."
Russell, who became
an assistant professor at Princeton in February, studies aerosol
chemistry. In scientific terms, the aerosol is the number of mostly
invisible particles in the air; what Russell does on her research
flights is count the number of these particles and determine their
chemical composition.
Since 1992 she has been using this data to study the effect of both these factors on cloud structure and cooling. It's a quest that has taken her to the skies all over the world, from the LA basin to Tasmania to Tenerife -- and that's only in the past three years. This year she received a Young Investigator Award from the Office of Naval Research and a New Faculty Award from the Camille and Henry Dreyfus Foundation.
The atmosphere, Russell explains, has as many layers as an invisible Sachertorte, if the cake were about 20 miles high. "Pollutants vary a lot with altitude, and unless you understand the vertical structure of the atmosphere, you don't know if the chemicals and particles you detect are going up, where they may last months, or down, where they'll disappear in days." Flying and collecting at various levels will enable her to build up a portrait of this cross-section.
So why won't the pilots do what she wants? Russell concedes that they have some pretty good reasons. Having logged hundreds of hours aloft, she knows that updrafts and downdrafts make it hard to maintain a constant altitude. At 28,000 feet in a commercial airliner, a bump of 100 feet might make you spill your coffee; skimming the ocean in a C-130, a similar bump would have more serious consequences.
Still, the thought of all that data just out of reach is maddening. "It's fortunate I'm not a licensed pilot," says Russell, "because in this case the goals of science and of safety are sort of diametrically opposed. It's probably good to have people flying the plane who don't have so much vested interest in the data I'm trying to get."
Cheap, smoky brown coal
When Russell first became interested in air pollution, altitude wasn't a problem. As a double major in chemical engineering and international relations at Stanford University, she spent part of her junior year in Berlin. The air quality was terrible at the time, mostly because the Eastern Bloc nations were still burning a lot of cheap, smoky brown coal for fuel. Russell ended up doing an honors thesis on air pollution in eastern Germany.
The thesis was written from a policy, rather than a scientific, perspective, but Russell ended up pursuing a doctorate in atmospheric chemistry. "I'm more attracted to the scientific aspect," she says, "to the problems that seem more solvable."
She opted for chemical engineering and chose California Institute of Technology for graduate work. There, in the course of her dissertation research, she took part in a five-week research cruise near the Azores. The scientists would release balloons that would drift with prevailing air currents; later, planes would track the balloons.
"I was frustrated being at the surface," she says. After finishing her PhD, she was invited to join the Advanced Studies Program of the National Center for Atmospheric Research and took to the skies.
Whiter clouds produce cooling
If building up a portrait of pollution layers were of purely academic interest, you could legitimately ask whether risking an ocean dunking might not be foolhardy. However, much more is at stake. The data Russell is collecting may turn out to have implications for worldwide climate and climate change.
Aerosol pollution, she explains, can actually change the structure of clouds. The number, size and chemical makeup of particles affect the size of moisture droplets in the clouds, and the number and size of droplets affect the clouds' whiteness. A hundred years ago the color of clouds mattered mostly to landscape painters; today the significance is much more profound.
"As clouds get whiter, they reflect more solar heat and produce a local cooling effect that has been dubbed the `whitehouse effect,'" Russell says.
Which brings her to the punch line: "There's a lot of uncertainty to this, but it's been estimated that in the polluted area, the magnitude of this cooling effect may be equal, but opposite in sign, to that of global warming."
In other words, by pumping particulates into the atmosphere, we humans may have been damping the warming trend caused by the green-house gas, CO2. By enacting more stringent clean air standards on particulate emissions, we could inadvertently take the cloud brakes off.
Equally ominous and also still very uncertain, increased cloud whiteness and other aerosol effects may be cooling the industrialized northern hemisphere while allowing the less-developed, less-polluted southern hemisphere to warm, says Russell. What such unequal heating could do to change global air circulation patterns is unknown.
"To me what's intriguing about the problem is that if we're changing the atmosphere's natural balance of heating and cooling, we should probably figure it out before it becomes irreversible," Russell says.
Bringing aircraft to students
Given the time squeeze, it's a good thing that Russell and her colleagues in atmospheric research have hit on a solution to the careful-pilot problem: remote-controlled aircraft. She, along with researchers at the Office of Naval Research, Naval Postgraduate School, Caltech and Department of Energy, have founded CIRPAS, the Center for Remote Piloted Aircraft Studies. The group took delivery of the first of their two planes in 1996.
These aircraft may be light on personnel, but they're loaded with equipment. Russell and a colleague from Caltech have a patent pending on a machine called a radially classified aerosol detector that will be mounted in the front of the plane. A satellite link allowing researchers to see data on ozone, temperature and aerosol in real time is already up and running. And a video link is in the works, so Russell and her students will be able to see what the plane is seeing displayed on their desktop computers.
"We'd love to take a bunch of students up in a plane to let them learn about making measurements in the atmosphere, but since research aircraft are continually in use by many different research projects, we've designed a way to bring the aircraft to the students," Russell says.
There are still a few glitches in the system, Russell admits. For one thing, the remote piloting communications and algorithms -- which allow the pilot and scientists on the ground to guide the mission and "to tell it to come back to base and not crash into things" -- continue to be developed. Still, the planes can do 22-hour flights over the ocean, at high or low altitude, without making anyone nervous.
Yet Russell confesses that when the automation is complete, she'll miss the planes. "In the lab, you tend to forget all the uncertainties there are in atmospheric science. Flying is a good way to remind yourself."
Of course, there's always bungee jumping.
1215-russell.html