Introduction
The overall objective of the NASA Atmospheric Effects of Aviation Project (AEAP) is to develop scientific bases for assessing atmospheric impacts of the exhaust emissions discharged during cruise operations by fleets of subsonic and supersonic civil aircraft. The AEAP is comprised of two major entities, the Subsonic Assessment (SASS) project and the Atmospheric Effects of Supersonic Aircraft (AESA) project. The SASS project is being conducted under the auspices of NASA's Advanced Subsonic Technology Program (ASTP), and the AESA project under those of NASA's High-Speed Research Program (HSRP). Because of their shared focus on environmental impact, program management of these two assessment efforts has been consolidated into an overall program, the AEAP.
The purpose of the SASS project is to assess the possible impacts of both current and future fleets of subsonic civil transport aircraft. At cruise altitudes these aircraft operate in the upper troposphere and the lower stratosphere. The AESA project, on the other hand, is designed to assess the impacts of a potential future fleet of high-speed civil transports (HSCTs). These supersonic aircraft are expected to feature the use of advanced aircraft and engine technology being evolved in the NASA HSRP. Their cruise operations will take place at midstratospheric altitudes (in the range of 16 to 20 km).
The AESA project, which was initiated first, has been in progress for about six years. Its current status is summarized in 1995 Scientific Assessment of the Atmospheric Effects of Stratospheric Aircraft (Stolarski et al., 1995). The SASS project was started in 1994. Its current status is summarized in Atmospheric
Effects of Aviation: First Report of the Subsonic Assessment Project (Thompson et al., 1996).
Among the six primary elements of the AEAP are Emissions Characterization (Element 9.6) and Near-Field Interactions (Element 9.5). The objective of the Emissions Characterization effort is to determine the exhaust-emission constituents and levels discharged at cruise operating conditions by current-technology subsonic-transport aircraft engines, projected future advanced-technology subsonic engines, and projected advanced-technology supersonic-transport engines equipped with ultra-low-emission combustors. The objective of the Near-Field Interactions effort is to determine whether and how fluid dynamic, chemical, and/or physical processes in aircraft wakes can alter the engine-emission constituents or their deposition altitude.
The NRC's Panel on Atmospheric Effects of Aviation (PAEAN) was requested to evaluate the appropriateness of AEAP's research plan, appraise the project's results, and suggest how best to reduce the remaining uncertainties. (An earlier panel did the same for the AESA project (NRC, 1994).) This report accordingly provides an interim assessment of the NASA Emissions Characterization and Near-Field Interactions efforts conducted to date, as summarized in the two publications mentioned earlier. It is intended to aid in detailed planning of the future work of these two AEAP elements. A second PAEAN report, Interim Review of the Subsonic Assessment Project: Management, Science, and Goals (NRC, 1997), makes recommendations for the SASS component. A third report, dealing with AESA, is in process.
