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7 II.1 Project Stages and Tests Figure II-1 depicts the four stages of this project. The first stage involved developing a test matrix suitable for probing near-idle engine states using in-service aircraft engines. The second and fourth stages were conducted at a cold weather airport in winter. For the third stage, the detailed probe work was conducted at a warm weather airport. We quantified emissions from both staged aircraft and in-use aircraft. Staged aircraft tests involved running tests on an out-of-service aircraft under controlled conditions using a test matrix developed specifically for this project. Testing was conducted using one of four exhaust sampling methods (three based on a one-meter probe and one using the mobile laboratory as a mobile probe). A total of 12 aircraft were sampled with this approach at three airport campaigns: MDW 2009, DAL 2010, and MDW/ORD 2010. The analysis of these test results form the basis of the temperature dependence of the near-idle HAP/VOC emission indices. In addition to the staged aircraft sampling, the emissions from in-use aircraft were also quantified. These tests were conducted in the provisional days at the end of each test, once the scheduled staged work was completed. To charac- terize the VOC emissions of in-use aircraft, exhaust plumes were continuously sampled and analyzed using high-time- response instrumentation downwind of an active taxiway. This approach measures diluted engine exhaust plumes formed under true operational conditions. Aircraft tail numbers were recorded and matched to time-coded video records to allow attribution of specific combustion plumes to the correspond- ing source engines. The in-use aircraft tests were conducted at various ambient temperatures and included a variety of aircraft engine types and taxiway operational throttle points. The analysis of the naturally diluted plume characterization produces a distribution of emission indices arising from air- craft operating with unknown fuel flow rates. To the extent that the precision in the trends observed in the staged aircraft testing is robust, the operational testing can yield information about the in-use engine state (Herndon et al. 2009). This type of data can also be used to investigate whether there are near- field atmospheric processes that could skew or undermine the effective use of an emissions inventory based exclusively on exhaust plane characterization. II.2 Test Venues, Temperatures, and Engines An overview of the test venues, ambient temperatures, and engines sampled is presented in Table II-1. In the MDW 2009 test, a subset of the complete instrument suite was deployed to characterize engine exhaust using a preliminary version of the test matrix that employed the mobile laboratory for sample acquisition. In the DAL 2009 test, the same subset of analytical equip- ment was deployed, but the sampling probe developed by Robert Howard (Arnold Engineering Development Center) was coupled to the probe stand developed by Phil Whitefield (Missouri University of Science and Technology). At DAL 2009, various test protocols were used to compare and evaluate sampling methodologies using a probe and stand situated behind the aircraft engine. These included the use of a heated transfer line, immediate dilution at the probe tip, and dilution plus pressure drop. The same aircraft was also characterized on an abbreviated test matrix using the mobile lab sampling methodology used in the first test. In the MDW 2010 test, a comprehensive set of instru- ments was used, including the instrumentation deployed by the Pacific Northwest National Laboratoryâs Environmental Molecular Sciences Laboratory. For the ORD 2010 test, the mobile laboratory sampling method was used for two dif- ferent engine technologies (non-CFM56) that had not been previously studied. S e c t i o n i i Project Plan and Approach
8This project also seeks to construct an empirically based model that will estimate VOC emissions as a function of fuel flow and ambient temperature. The methodology this work adopts is to treat fuel flow and ambient temperature as param- Figure II-1. Chronological depiction of the project stages. Table II-1. Testing overview. Te st En gi ne Ty pe s Te mp er at ur e MD W 2009 St ag ed CF M 56- 3B 1 -8 °C to -4 °C CF M 56- 7B 24 Ai rp or t Ta xi wa y Va ri ou s DA L 2009 St ag ed CF M 56- 7B 24 23° C to 25° C Ai rp or t Ru nw ay Va ri ou s MD W 2010 St ag ed CF M 56- 7B 24 -6 °C to -4 °C Ai rp or t Ta xi wa y Va ri ou s OR D 2010 St ag ed V 2527- A5 -3 °C to 2° C PW 4090 Airport Taxiway eters that influence the VOC emission index independently. Following the description and quantification of the near-idle fuel flow dependence, the data related to the ambient tem- perature dependence will be discussed.