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24 JETS-APEX 2 was similar to the Delta Atlanta-Hartsfield at both idle and takeoff is less than half that for the older study in that it included a second series of experiments focus- technology -3B series. ing on emissions sampled during normal airport operations In some cases, because of the unique aircraft traffic pat- from plumes transported downstream of the active taxiway terns, sampling location, and prevailing wind direction at and runway. The results of these downwind studies continue to OAK, takeoff and taxi plumes for different aircraft are found be analyzed, and the analysis to date has been summarized in to mix prior to sample extraction, greatly complicating two conference proceedings (Whitefield et al. 2007, Herndon data interpretation. The PM data from these mixed plumes et al. 2007). The major conclusions reported are broadly con- can be de-convolved to yield single aircraft specific infor- sistent with those from the Delta Atlanta-Hartsfield down- mation and such analysis is currently underway. wind studies. Specific conclusions include: 5.4 APEX3 As the plume expands and mixes with the ambient air, a large number of small particles are produced. These APEX3 is the most recent field study, and reporting on nucleation/growth mode particles are not present at the APEX3 data has not progressed as far as the earlier studies. exhaust nozzle. Although most data are available through the FAA, it has not The production of the small particles increases the number- been interpreted and reported, as is the case for the previous based emission index by at least an order of magnitude APEX-type studies discussed in this document. Furthermore, relative to samples acquired at the exhaust nozzle. the archived PM data have not been corrected for sample line The nucleation/growth particles do not significantly con- loss, as was the case in the previous studies. Preliminary tribute to the mass-dependent parameter values, and no analyses were presented at the APEX3 conference held in significant changes in the mass-based emission index are November 2006 (Hagen et al. 2006) and these could be used observed. to draw some qualitative results and intercomparisons. NASA The -3B series takeoff mass-based emission indices were may coordinate a final report, but that report was not available significantly greater than those for its taxi emissions and before publication of this ACRP document. For these rea- for both takeoff and taxi emissions for the -7B series. On sons, any reference to APEX3 data in this report exclusively average, the mass-based emission index for the -7B series, applies to Missouri S&T and ARI data available at press time.