TECHNOLOGY UPDATE High-flying instrument helps scientists evaluate aircraft impacts Atmospheric scientists are currently analyzing data depicting the most detailed portrait yet of military and space aircraft emissions. The data were captured by an ultrasensitive mass spectrometer developed to help the military comply with its Clean Air Act requirements. Some analysis results are expected to be published this month. The new instrument was created with funding from the Strategic Environmental Research and Development Program, which is jointly sponsored by EPA, the Department of Energy, and the Department of Defense. The mass spectrometer is capable of measuring emissions at the part-per-trillion level and can sample every hundredth of a second. Its combination of sensitivity, time responsiveness, portability, and ruggedness make it unique, according to John Ballenthin the atmospheric physicist who spent fi^g years as part of the team that designed and refined it for the Air Force Research Laboratory in Hanscom Mass Rouehlv one-half to one-third the instrument is installed insirle a chase nlane that follows behind a ipt airnlanp or rocket to analyze its •
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After aircraft emissions leave the engines, they begin chemically reacting with each other and with the surrounding environment, explained Ballenthin. "To understand the effect of the emissions upon the Earth's environment, you want to trace the evolution of the chemistry in the aircraft exhaust from as close as you can get, to several kilometers away, to months after the aircraft goes by," he said. To capture that data, the prototype instrument was flown through aircraft contrails and exhaust plumes
in a series of over 100 flights conducted between 1995 and 1998 by both the Air Force and National Aeronautics and Space Administration (NASA). For example, in June 1997, NASA supplied F-16 fighter jet pilots with fuel containing various sulfur levels to determine the effect of fuel sulfur content on aircraft emissions. The chase plane contain-
Atmospheric scientists monitor instrument performance aboard a chase plane as it monitors emissions from military aircraft.
ing the mass spectrometer got to within 50 meters of the F-16s while they were flying in formation, Ballenthin recalled. The data from those flights, which include measurements of sulfur, sulfuric acid, and nitric acid content in the jet emissions at altitudes ranging from 10,000 to 41,000 feet, is still being analyzed. In another NASA-funded flight series, Ballenthin's instrument was used to measure "well-aged plumes" over the mid-Atlantic flight corridor the world's busiest he said. Analysis of the data allowed scientists to differentiate between plumes that had originated in jet aircraft "days weeks and even months prior" he explained This series of flights focused on measuring nitric acirl rnnrpntratinnQ Oiiring that instrument was
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able to recognize a plume of air that later analysis proved to come from a smelting plant in Ontario, Canada. "Nitric acid is an important component in trying to understand the interaction of the aerosols and the chemistry in the upper atmosphere, and so a good measurement of nitric acid certainly will help us in determining the overall chemical mixture and whether or not the exhaust from the aircraft is affecting that chemical mixture," said Donald Anderson, project scientist for NASA's Atmospheric Effects of Aviation Project at Goddard Space Center in Greenbelt Md. The Air Force and NASA also used the mass spectrometer as part of a payload that made the first stratospheric measurements of the fate of Space Shuttle, Titan W, and Delta rocket exhausts. After the rockets were launched, a WB57F high-altitude aircraft containing the instrument zipped back and forth through the solid rocket fuel emissions at 61,000 feet. "Our instrument was able to measure the hydrochloric acid emitted from the solid fuel rocket engines and see the HC1 converted to molecular chlorine in the exhaust plume of the rocket" Though models had predicted this chemical reaction, it was the first time the reaction was actually measured in the stratosphere. The instrument also was used to measure the rocket exhausts' concentration of atomic chlorine, molecular chlorine, and chlorine oxide; the latter is implicated in the destruction of ozone in the stratosphere. Preliminary results from this rocket testing campaign are expected to be presented at the American Geophysical Union meeting this month. "A lot of the data was unexpected," Ballenthin said. The conversion of hydrochloric acid to molecular chlorine proved to be lower than what the models predicted, and the molecular chlorine
0013-936X/98/0932-538A$15.00/0 © 1998 American Chemical Society
persisted for longer than predicted, he said. The ultrasensitive mass spectrometer is particularly well suited for characterizing acid-type emissions, he said. "It's a very selective technique," he explained. The instrument's selectivity can be "tuned" to target particular classes of compounds by modifying the ionization process at the input of the instrument, he said. This device is particularly well suited for monitoring fast-changing events such as how aircraft emissions mix with other gases in the atmosphere, Ballenthin said. In a recent test, the instrument was able to take measurements at 50 parts per billion accuracy per second. The instrument has since been refined so that it is capable of making even more precise measurements, Ballenthin said. Ultimately, he is aiming for the instrument to reach the 100-parts-per-quadrillion detection level.) On the same flight a mist chamber ion chromatograph
SIMPLE EXPERIMENT WITH MOUSE YIELDS AMAZING DISCOVERIES FOR CHEMISTS
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able to obtain measurements with the minutes The Air Force Research Laboratory is presently in the process of formalizing an agreement with a Massachusetts company that hopes to use the mass spectrometer for characterizing exhaust from oceangoing Navy ships. Ballenthin estimates it would cost $200,000 to produce the instrument, which could also prove useful for detecting chemical weapons, as well as explosives in airports. It also has potential applications for pollution monitoring Ballenthin said. NASA plans to use some of the data collected by the new instrument to attempt to predict the future climatic effects of increasing the world's fleet of commercial supersonic aircraft. The space agency also hopes to use the data to ascertain whether or not the emissions from subsonic commercial aircraft increase cloudiness, which could change the radiation balance in the Earth's atmosphere and ultimately affect climate Anderson said. Data from the project will also be used in a special report on aviation and the global atmosphere expected to be published by the International Panel on Climate Chanee bv the end of the KELLYN S. BETTS Vpar
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