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10/28/2003 08:00:00

Atmospheric scientists still acquire samples the old-fashioned way--by flying up and getting them

PASADENA, Calif.—Just as Ishmael always returned to the high seas for whales after spending time on land, an atmospheric researcher always returns to the air for new data.

All scientific disciplines depend on the direct collection of data on natural phenomena to one extent or another. But atmospheric scientists still find it especially important to do some empirical data-gathering, and the best way to get what they need is by taking up a plane and more or less opening a window.

At the California Institute of Technology, where atmospheric science is a major interest involving researchers in several disciplines, the collection of data is considered important enough to justify the maintenance of a specially equipped plane dedicated to the purpose. In addition to the low-altitude plane, several Caltech researchers who need higher-altitude data are also heavy users of the jet aircraft maintained by NASA for its Airborne Science Program--a longstanding but relatively unsung initiative with aircraft based at the Dryden Flight Research Center in California's Mojave Desert.

"The best thing about using aircraft instead of balloons is that you are assured of getting your instruments back in working order," says Paul Wennberg, professor of atmospheric chemistry and environmental engineering science. Wennberg, whose work has been often cited in policy debates about the human impact on the ozone layer, often relies on the NASA suborbital platforms (i.e., various piloted and drone aircraft operating at mid to high altitudes) to collect his data.

Wennberg's experiments typically ride on the high-flying ER-2, which is a revamped reconnaissance U-2. The plane has room for the pilot only, which means that the experimental equipment has to be hands-free and independent of constant technical attention. Recently, Wennberg's group has made measurements from a reconfigured DC-8 that has room for some 30 passengers, depending on the scientific payload, but the operating ceiling is some tens of thousands of feet lower than that of the ER-2.

"The airplane program has been the king for NASA in terms of discoveries," Wennberg says. "Atmospheric science, and certainly atmospheric chemistry, is still very much an observational field. The discoveries we've made have not been by modeling, but by consistent surprise when we've taken up instruments and collected measurements."

In his field of atmospheric chemistry, Wennberg says the three foundations are laboratory work, synthesis and modeling, and observational data--the latter being still the most important.

"You might have hoped we'd be at the place where we could go to the field as a confirmation of what we did back in the lab or with computer programs, but that's not true. We go to the field and see things we don't understand."

Wennberg sometimes worries about the public perception of the value of the Airborne Science Program because the launching of a conventional jet aircraft is by no means as glamorous or romantic as the blasting off of a rocket from Cape Canaveral. By contrast, his own data-collection would appear to most as bread-and-butter work involving a few tried-and-true jet airplanes.

"If you hear that the program uses 'old technology,' this refers to the planes themselves and not the instruments, which are state-of-the-art," he says. "The platforms may be old, but it's really a vacuous argument to say that the program is in any way old.

"I would argue that the NASA program is a very cost-effective way to go just about anywhere on Earth and get data."

Chris Miller, who is a mission manager for the Airborne Science Program at the Dryden Flight Research Center, can attest to the range and abilities of the DC-8 by merely pointing to his control station behind the pilot's cabin. On his wall are mounted literally dozens of travel stick-ons from places around the world where the DC-8 passengers have done research. Included are mementos from Hong Kong, Singapore, New Zealand, Australia, Japan, Thailand, and Greenland, to name a few.

"In addition to atmospheric chemistry, we also collect data for Earth imaging, oceanography, agriculture, disaster preparedness, and archaeology," says Miller. "There can be anywhere from two or three to 15 experiments on a plane, and each experiment can be one rack of equipment to half a dozen."

Wennberg and colleagues Fred Eisele of the National Center for Atmospheric Research and Rick Flagan, who is McCollum Professor of Chemical Engineering, have developed special instrumentation to ride on the ER-2. One of their new instruments is a selected-ion- chemical ionization mass spectrometer, which is used to study the composition of the atmospheric aerosols and the mechanisms that lead to its production.

Caltech's Nohl Professor and professor of chemical engineering, John Seinfeld, conducts an aircraft program that is a bit more down-to-earth, at least in the literal sense.

Seinfeld is considered perhaps the world's leading authority on atmospheric particles or so-called aerosols--that is, all the stuff in the air like sulfur compounds and various other pollutants not classifiable as a gas. Seinfeld and his associates study primarily atmospheric particles, their size, their composition, their optical properties, their effect on solar radiation, their effect on cloud formation, and ultimately their effect on Earth's climate.

"Professor Rick Flagan and I have been involved for a number of years in an aircraft program largely funded by the Office of Naval Research, and established jointly with the Naval Postgraduate School in Monterey. The joint program was given the acronym CIRPAS," says Seinfeld, explaining that CIRPAS, the Center for Interdisciplinary Remotely Piloted Aircraft Studies, acknowledges the Navy's interest in making certain types of environmental research amenable for drone aircraft like the Predator.

"The Twin Otter is our principal aircraft, and it's very rugged and dependable," he adds. "It's the size of a small commuter aircraft, and it's mind-boggling how much instrumentation we can pack in this relatively small aircraft."

Caltech scientists used the plane in July to study the effects of particles on the marine strata off the California coast, and the plane has also been to the Canary Islands, Japan, Key West, Florida, and other places. In fact, the Twin Otter can essentially be taken anywhere in the world.

One hot area of research these days, pardon the term, is the interaction of particulate pollution with radiation from the sun. This is important for climate research, because, if one looks down from a high-flying jet on a smoggy day, it becomes clear that a lot of sunlight is bouncing back and never reaching the ground. Changing atmospheric conditions therefore affect Earth's heat balance.

"If you change properties of clouds, then you change the climatic conditions on Earth," Seinfeld says. "Clouds are a major component in the planet's energy balance."

Unlike the ER-2, in which instrumentation must be contained in a small space, the Twin Otter can accommodate onboard mass spectrometers and such for onboard direct logging and analysis of data. The data are streamed to the ground in real time, which means that the scientists can sit in the hangar and watch the data come in. Seinfeld himself is one of those on the ground, leaving the two scientist seats in the plane to those whose instruments may require in-flight attention.

"We typically fly below 10,000 feet because the plane is not pressurized. Most of the phenomena we want to study occur below this altitude," he says.

John Eiler, associate professor of geochemistry, is another user of the NASA Airborne Research Program, particularly the air samples returned by the ER-2. Eiler is especially interested these days in the global hydrogen budget, and how a hydrogen-fueled transportation infrastructure could someday impact the environment.

Eiler and Caltech professor of planetary science Yuk Yung, along with lead author Tracey Tromp and several others, issued a paper on the hydrogen economy in June that quickly became one of the most controversial Caltech research projects in recent memory. Using mathematical modeling, the group showed that the inevitable leakage of hydrogen in a hydrogen-fueled economy could impact the ozone layer.

More recently Eiler and another group of collaborators, using samples returned by the ER-2 and subject to mass spectroscopy, have reported further details on how hydrogen could impact the environment. Specifically, they capitalized on the ER-2's high-altitude capabilities to collect air samples in the only region of Earth where's it's simple and straightforward to infer the precise cascade of reactions involving hydrogen and methane.

Though it seems contradictory, the Eiler team's conclusion from stratospheric research was that the hydrogen-eating microbes in soils can take care of at least some of the hydrogen leaked by human activity.

"This study was made possible by data collection," Eiler says. "So it's still the case in atmospheric chemistry that there's no substitute for going up and getting samples."

Written by Robert Tindol