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22 CHAPTER 8 Proposed Research Agenda and Problem Statements Concern about particulate matter (PM) emissions from air- 3. Reviewing airport emissions data for source chemical craft engines and other emission sources at airports is increas- markers or fingerprints is proposed as a synthesis proj- ing as demand for air travel grows. Without better information ect. PM emissions from various airport sources combine about PM emissions, airports will face increasing barriers to as they move off the airport and it is difficult to isolate expansion. This paper has provided a detailed assessment of individual emission sources, for example, when evaluat- current knowledge on PM emissions and has identified the ing the impact of airport operations on nearby commu- gaps that exist in our knowledge of airport-related PM. With nities. It would be a significant benefit to airports if there this in mind and an understanding of other research initiatives were characteristic markers or "fingerprints" that were that address this interest area, two problem statements and a unique to individual sources. Some airport emission synthesis report are proposed for future ACRP funding that sources have been studied individually and others are address the following three high-priority research needs. proposed in our top priority project. These studies will produce data such as particle size number, mass, and 1. Characterizing PM emissions of GSE, APUs, tires, and composition that can serve as a resource for this pro- brakes for source apportionment is our first priority pro- posed synthesis project. posal. These emissions remain either unknown, or at best, poorly characterized and represent a unique focal point Combined, these projects will eliminate critical knowledge for ACRP. Reliance on any existing estimates of such gaps identified in this report. The data these projects yield will emissions to predict emissions inventories for future permit the airport community to prepare credible and accu- airport activities is likely to result in significant overesti- rate future impact assessments. Detailed problem statements mations, which may impose unnecessary restrictions on are presented at the end of this chapter. needed expansion. As noted in previous chapters, PM emissions from aircraft 2. Developing an understanding of the atmospheric evolu- main engines represent possibly the most significant gap in tion of aviation PM is our second priority project pro- our understanding of all airport emissions. Existing emis- posal. One distinguishing feature of aviation emissions is sions data have been acquired on older technology engines. the significant presence of volatile particle precursors Although these engines represent a significant fraction of the that condense on preexisting particles or nucleate new current commercial fleet they are not representative of the PM, forming nanometer-sized particles as hot exhaust engines in the next generation air transportation system. gases cool. Information regarding the evolution of these FAA's PARTNER research program, NASA, and DOD, how- particles, especially in the near field, is required to assess ever, have already identified the development of a broader airport impacts on airport workers, passengers, and the aircraft emissions database as the most pressing need for the local community. The mechanisms and time-scales of entire air transportation system and the constituencies they these processes are poorly understood, however, as are serve, especially for newer technology engines. Combined the contributions from the various sources. To address they have recently proposed multiyear, multimillion-dollar this lack of understanding, a study of the atmospheric research programs to address these needs. For this reason, we evolution of PM emissions--coupling operational fac- are not proposing that ACRP initiate main engine testing tors with source emissions in the near and far field--is programs, however, it should continue to monitor progress needed. in this area. This may also be a fruitful area for information