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14 that sampled the exhaust plume gases without introducing any dilution because exhaust plume was already diluted significantly with ambient air. Samples to all particle instru- ments were distributed through the sample distribution manifold. Modification of the aerosol size and composition due to various mechanisms such as inertia, thermophoresis, and diffusional effects, can occur in the sample train and are accounted for with calibration experiments (Lobo, Hagen et al. 2007). Gas samples (undiluted) were transferred through about 30 m (98 ft) of heated (177°C [350°F]) sampling line and distributed to individual instruments. 3.2 Delta Atlanta-Hartsfield Study The second of the APEX series of studies was carried out Figure 5. Probe rake assembly used during Phase 1 with the support of Delta Airlines at Hartsfield-Jackson of the Delta Atlanta-Hartsfield Study. Atlanta International Airport in September 2004. Mobile laboratories operated by Missouri University of Science and Technology (Missouri S&T), Aerodyne Research, Inc. (ARI), opportunity to measure PM and gaseous emissions from in- and the National Oceanic and Atmospheric Administration service commercial transports. (NOAA) were deployed to conduct two series of measure- Dedicated engine tests on stationary aircraft took place be- ments of aircraft engine-generated PM emissions. The first tween 10:00 P.M. and 5:00 A.M. on September 21-25, 2004. The series was conducted at the maintenance facilities of Delta aircraft tested were selected from those scheduled to be Airlines and focused on PM emissions in the vicinity of the overnight at the airport. The exhaust plumes of each aircraft exhaust nozzle of several different aircraft whose engines were investigated using both probe sampling at the engine were cycled through a matrix of reproducible engine operat- exhaust nozzle exit (Missouri S&T-ARI), see Figure 5, and ing conditions as in APEX1. The second series introduced a remote sensing using LIDAR (light detection and ranging) novel approach focusing on emissions generated under actual (NOAA) at a point in the plume close to the exhaust nozzle exit, operational conditions. This series was conducted by placing thus permitting comparisons of measurement techniques. the mobile laboratories adjacent to, and downstream of, Another objective was a study of engine-to-engine variation active runways. In these latter measurements advected exhaust within the same class and, where possible, two aircraft with plumes generated by a broad mix of commercial transport the same engine class were studied. The airframes and engines aircraft taxiing and departing the airport during normal oper- studied are listed in Table 1. ations were detected and analyzed. The range of engine operating conditions examined focused The Atlanta study was originally subject to nondisclo- on the LTO cycle with additional intermediate settings. For sure agreements between the research team and Delta the JT8Ds, the complete range of thrust settings was explored, Airlines and, until December 2006, was referred to as the but for the higher thrust engines, transient instabilities in- Un-Named Airline--Un-Named Airport (UNA-UNA) Study. duced vibration in the probe stands at mid- to high thrust, In November 2006, the nondisclosure statement was re- and this limited the range of thrusts sampled. scinded, permitting the public release of the data, and the The probe sampling measurements by Missouri S&T focused study was henceforth known as the Delta-Atlanta Hartsfield on physical characterization measurements including particle Study. The Delta-Atlanta Hartsfield Study was the first size distribution, number- and mass-based emission indices Table 1. Airframes and engines measured during the Delta-Atlanta Hartsfield Study. Date Aircraft Airframe Engine Thrust Number (kN) September 22, 2004 908 MD-88 JT8D-219 93 September 23, 2004 918 MD-88 JT8D-219 93 September 23, 2004 134 B767-300 CF6-80A2 217 September 24, 2004 1816 B767-400ER CF6-80C2B8F 258 September 24, 2004 635 B757-200 PW 2037 166 September 25, 2004 640 B757-200 PW 2037 166