Mass Distribution and Concentrations of Negative Chemiions in the Exhaust of a Jet Engine: Sulfuric Acid Concentrations and Observation of Particle Growth

Measurements of negative-ion composition and density have been made in the exhaust of a J85-GE-5H turbojet, at ground level, as part of the NASA-EXCAVATE campaign. The mass spectrometer was placed 3 m from the exhaust plane of the engine. Measurements were done as a function of engine power in six steps from idle (50%) to military power (100%). Since the exhaust velocity changes with power, this also corresponds to a time evolution for ion growth. At 100% power most of the ions are HSO-4 with minor amounts of HSO-4(H2O)n-. With decreasing engine power the degree of hydration increases. In addition, ions with a 139-amu core dominate the spectra at lower engine power. The chemical identity of this ion is unknown. Observation of a small amount of NO-3 core ions in the high-power spectra allows the determination of H2SO4 concentrations, which turn out to be a fraction-of-a-percent of the total sulfur in the fuel. Combining the present data with several previous composition measurements allows one to observe ion evolution from bare ions to ions with masses 8000 amu. Ion densities are derived and appear consistent with previous measurements used in modeling studies indicating that ion nucleation is a probable mechanism for volatile aerosol formation. Pub. in Atmospheric Environment, v39 p3069-3079, 2005. Prepared in cooperation with National Aeronautics and Space Administration (NASA), Atmospheric Sciences Division, Langley Research Center, Hampton, VA, and Army Research Laboratory, Engine Components Division, NASA, Glenn Research Center, Cleveland, OH. Sponsored in part by the NASA Atmospheric Effects of Aviation Project, the Air Force Office of Scientific Research (AFOSR), and the Strategic Environmental Research and Development Program (SERDP).