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24 reiterated that care must be taken when backcasting and/or Aircraft Method 1 forecasting since the data (e.g., source activities, emission fac- Emission Factors tors, etc.) to support these processes may not be very accurate. Airport Fuel and Other Data as EDMS Sales Data Necessary 3.1.4 Other Pollutants For some of the pollutants in Level 3 (beyond the six Kyoto Aircraft LTO Fuel pollutants in Level 2), AEDT/EDMS could be used to derive Calculate Consumption inventories for many of these pollutants, but only for the LTO portion. The inventory developer will need to determine the usefulness of such data based on airport needs. IPCC pro- Total Aircraft GHG Calculate vides cruise-related emission factors for NOx in Volume 2, Emissions HG Chapter 3, Table 3.6.10 of its guidelines (IPCC 2006). Poten- P U G ions A is s tially, the fuel use derived from Method 2 could be used with Em these emission factors. Emissions of H2O and SOx can be esti- mated using fuel composition data with mass balance, as indi- Aircraft LTO GHG Subtract Emissions cated in Appendix C. Emissions of fluorinated compounds (e.g., HFC and PFC) from fire extinguishers can also be taken into account. Vol- ume 3, Chapter 7 of the IPCC guidelines (IPCC 2006) and Aircraft Cruise GHG Emissions Annex 3 of the EPA inventory report (USEPAb 2008) provide HG P U G ions methods and data for calculating emissions from fire extin- A iss Em guishers. Discussions with manufacturers and airlines have indicated that no data currently exists to directly support the Figure 3-4. APU emissions accounted as part of modeling of emissions from the Halon systems on an aircraft aircraft emissions using either Aircraft Method 1 (Bennett 2008; Valeika 2008). (upper box) or Aircraft Method 2 (overall figure). 3.2 Auxiliary Power Unit The International Coordinating Council of Aerospace At this time, APU-related GHG emissions can only be ac- Industries Association (ICCAIA) is developing an APU data- counted for through Aircraft Methods 1 and 2 (fuel sales data). base to be managed by the Swedish Defense Research Agency As discussed later in this section, a subsequent dataset is ex- (FOI). The database is expected to contain fuel consump- pected to be released in the future, which will reflect the abil- tion and CO2 emission factors. However, under directions ity to separately itemize APU emissions. from ICCAIA and the manufacturers, it is expected that The fuel used by onboard aircraft APUs is accounted for in the Swedish FOI will only make the database available to the fuel sales data (fuel dispensed) as the main aircraft engines certain organizations (e.g., government agencies) for re- are powered by the same fuel that powers the APU. Therefore, search purposes and will likely have stipulations that the both Methods 1 and 2 in Sections 3.1.1 and 3.1.2, respectively, data not be published in any form. Another potential source account for APU fuel use, as shown in Figure 3-4. of APU data is a USEPA report entitled, "Technical Data to Although Aircraft Methods 1 and 2 account for APU emis- Support FAA's Advisory Circular on Reducing Emissions sions, it should be understood that the AEDT/EDMS (FAAa from Commercial Aviation" (1995). Although this docu- 2007) results for aircraft LTO fuel consumption, as shown in ment appears to be publicly available, it is not recommended Figure 3-4, presently do not include APU contributions. for use since it does not appear to have been intended for Therefore, since the LTO emissions are subtracted from the public review because it was never finalized. Therefore, total airport emissions to derive what is previously labeled unless the availability/usability of these datasets changes, cruise, the APU emissions would be included but as part of airports would not be able to specifically quantify APU the cruise emissions results for Method 2. This could poten- emissions outside of the total aircraft and cruise emissions tially be rectified as APU-specific fuel consumption and emis- determined from the Aircraft Methods 1 and 2, respec- sions data become available. Assuming the same combustion tively. If Aircraft Method 3 is used, the SAGE data would efficiency for jet engines, the same calculation methods from not include APU emissions because it only represents air- Section 3.1 can be used to convert APU fuel consumption to craft emissions. The inventory documentation should clearly APU emissions. indicate which of these methods was used, and the reasons