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23 The black carbon component of the PM emissions detected The amount of sulfate emitted by the CFM56 engines in the transported plume varies among engine types as is increased with fuel sulfur content, as did the number of par- observed at the exhaust nozzle. ticles formed in the diluting exhaust gas in the 30-m (98-ft) For all plumes sampled, the number-based emission index and 50-m (164-ft) samples. ranged from 3 1016 to 2 1017 particles/kg fuel and the The CFM56 engine exhaust did not contain substantial mass-based emission index ranged from 0.1 to 0.35 g/kg quantities of lubrication oil in the exhaust, even at high fuel. These averages, based on measurements of PM thrust. Lubrication oil contributed at most about 3mg/kg emissions from in-service aircraft during normal operating to the overall quantity of emitted organic PM. conditions, give credence to the rough averages reported in A significant fraction of the organic PM contained in the Intergovernmental Panel on Climate Change (IPCC) CFM56 exhaust appears to be UHC. Unburned hydrocar- report. (Penner et al. 1999) bons constitute as much as 80% of the CFM56 organic PM emissions at idle and as much as 70% at climb-out/takeoff. The measured ratio of sulfate to organic PM was greater 5.3 JETS-APEX2 at high thrust (climb-out and takeoff) than at low thrust The objective of the next APEX study, JETS-APEX2, was to (approach and idle) by a factor of at least three. The develop TOG and PM speciation profiles for engines used in observed thrust dependence is consistent with combustor newer Boeing 737-type commercial aircraft burning standard efficiency (and, therefore, HC emissions) being more Jet A fuel. These aircraft were specifically chosen since they sensitive to thrust condition than conversion of fuel sulfur represent greater than 70% of the aircraft currently in opera- to condensible species (i.e., SO3). tion in the domestic commercial fleet. The data from APEX1, Delta Atlanta-Hartsfield, and The JETS-APEX2 study aimed to produce a comprehen- JETS-APEX2 indicate that PM emissions depend on sive data set of emission factors for TOG and PM for older engine/airframe. (CFM56-3) and newer (CFM56-7) CFM56-class engines. The study was successful in producing the first state-of-the-art Upon the completion of this study, the following recom- measurements for PM physical characterization of in-service mendations for future aircraft emission characterization tests CFM56-type engines. were made: The major conclusions from the JETS-APEX2 study are as follows: Emissions studies of wider range of engines/airframes should now be performed (e.g., B747/CF6-80, etc.). The qualitative emissions trends observed are consistent The ideal testing conditions afforded by the GRE at OAK with those measured for the CFM56-2C1 engine studied in recommends the use of the GRE for future tests. the APEX1 campaign. Since the mix of transports routinely operating in and out At takeoff, the mass-based emission index for the -7B of OAK will limit the range of engines/airframes that can engines was significantly lower than that for the older tech- be studied, for future studies where B747, B757, B767, and nology -3B and -2C1 engines. At takeoff (typically 85% B777 and the larger Airbus transports A320, A340, etc. are rated thrust at OAK), the -7B mass-based emission index anticipated test vehicles, it will be necessary to consider was found to be four times less than that of the -3B. GREs located at other airports. NOX measurements were in good agreement with ICAO In future tests, engine operating data (e.g., N1--fan rotor certification data, indicating that the engines were in good speed [rpm], N2--core rotor speed [rpm], EGT--exhaust condition and lending credence to the assumption that gas temperature, fuel flow rate) should be recorded to the concomitant PM emissions are also representative of facilitate interpretation of emissions data. Ideally, engine an engine in good condition. operating data will be recorded at high-frequency and Most individual HC species decrease with increasing thrust made available in real time. Recording of engine data may in proportion to each other. As one of the most plentiful be difficult for older airframes, but straightforward for emitted hydrocarbons, formaldehyde is easily measured newer additions to the commercial fleet that digitally record and provides a good standard for comparing the emissions engine operating conditions. of other less abundant trace hydrocarbons. Engine-to-engine variability is difficult to estimate when The emission index of SO2 increases directly with fuel sul- the engine sample size is small (in this study 4 engines fur content. per model). The value of accurately estimating this Volatile particles are composed of both sulfate and organic parameter warrants the consideration of a longer period materials, adding to the carbonaceous aerosol that is present of study, allowing more engines of a given model to be already at the exhaust nozzle. studied.