Every day, thousands of jet aircraft fly through the Earth's atmosphere, but scientists are still uncertain how much pollution is produced. To better understand this relatively unknown source of air pollution, researchers at NASA's Langley Research Center, Hampton, VA, are measuring emissions from the engines of two NASA research jets -- Boeing 737 and a Boeing 757.

During a two-week experiment, as part of NASA's Atmospheric Effects of Aviation Project (AEAP), a NASA T-39 jet will fly behind a NASA 737. Instruments aboard the T-39 will measure various gases and small pollutant particles (called aerosols) emitted by the 737's engines. The T-39 data also will be used to study how the 737's engine emissions disperse in the atmosphere, and how rapidly. Jet engine emissions can often be seen in the atmosphere in the form of contrails flowing behind the aircraft.

The NASA 737 also will fly over a ground-based laser system at Langley that can measure the aerosols emitted from the engines. These aerosol measurements can be used as tracers to study how air flows around the jet, dispersing the emissions into the atmosphere. Jet engine emissions have been shown to affect the concentrations of atmospheric water vapor and aerosols, and they may affect how clouds form and the concentrations of atmospheric ozone. Few direct measurements of their effects have been made, however.

In addition to the ground-based laser system and the T-39, researchers from the University of Missouri-Rolla will measure engine emissions from both the 737 and the 757 in ground tests at Langley. Using a probe mounted near the rear of the engine, the University of Missouri researchers will measure the amount of aerosols emitted by each engine and the distribution of the particle sizes.

The data collected during this experiment will provide AEAP scientists with a unique data set to help them better understand how jet aircraft emissions are affecting our atmosphere and how these emissions are dispersed.

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