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4 is, however, so prevalent in aircraft emissions literature, described here employs on-wing engine testing, pulling air- we continue to employ it in this document. craft from active commercial service of cooperating airlines. The test matrix used in this project includes the engine state defined in the certification databank (ICAO 2006), but also I.1Aircraft Engine Emissions includes engine states that reflect airport operational conditions at Airports developed with advice from airline propulsion engineers. The Government agencies and community groups frequently inclusion of different engines, each with a different maintenance ask airport operators to provide information that enables an history, implies that there may be variability in the results, assessment of the health impacts of toxic emissions from air- particularly when probing an engine state far removed from craft and other airport-related sources. Two important catego- the optimal combustor design. This project will attempt to ries of pollutants, as classified by the Clean Air Act, are criteria "see through" whatever variability is present in the key data pollutants (comprising particulate matter, ground-level ozone, trends and develop a simple methodology that can be used to carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead) estimate HAP emissions at different ambient temperatures and HAPs (e.g., benzene and formaldehyde). Information on and in-use fuel flow rates at the airport. the emission, transformation, and transport of aviation-related Although every airport is unique and universal statements HAPs and their health impacts is rudimentary. Without a bet- are not appropriate, several airport emission inventories ter understanding of aviation HAP emissions, airport operators report that the greatest source of HAP emissions is idling jet cannot develop accurate emission inventories or adequately engines (Wood et al. 2008). At power (thrust) settings greater respond to the queries from state and local constituencies. than idle, the combustion efficiency of modern jet engines The ACRP 02-03 study was undertaken in 2007 to examine is high, and emissions of carbon monoxide (CO) and VOCs, and identify gaps in research on airport-related HAP emis- which are products of incomplete combustion, are thus small. sions and to recommend and prioritize additional research Many of the VOCs are partially oxidized combustion hydro- to help understand potential impacts of those emissions. The carbons and are classified as HAPs (e.g., acetaldehyde). Aircraft study findings were published in ACRP Report 7: Aircraft and engines operating at idle power settings are responsible for the Airport-Related Hazardous Air Pollutants: Research Needs and majority of HAP emissions generated during landing/takeoff Analysis, which concluded that idling jet engines are a key (LTO) cycles. This point can be illustrated by examining data source of airport-related HAPs at most commercial airports from the emissions performance databank maintained by (Wood et al. 2008). Understanding the scale and character the International Civil Aviation Organization (ICAO). In of this emission source is a high priority for the airport Figure I-1, the emissions data (expressed as unburned hydro community. The report recommended a targeted research carbon [UHC]) is depicted for an LTO cycle at an airport. The effort to document the contribution of idling jet engines to relationship between UHC and the gaseous HAP compounds HAP emissions. This report describes the resulting research has been established previously (Herndon et al. 2009) and project and the development of a model to estimate emissions will be expanded later. from engines operating at near-idle engine states. In Figure I-1, the emission rate is estimated as a function of Testing from earlier measurement campaigns conducted time during a hypothetical operation. The estimate depicted by as part of the Aircraft Particle Emissions Experiment (APEX) the solid line is based on the tabulated emissions performance in 2004 and 2005 (Herndon et al. 2009, Knighton et al. 2007, data for aircraft equipped with two CFM56-2B24 engines Timko et al. 2010, Wey et al. 2006, Yelvington et al. 2007) confirmed that emissions of VOCs from modern jet engines, many of which are classified as HAPs, are relatively small at medium and high power settings, but higher at low power settings (engine idle) (Spicer et al. 1994). Notwithstanding the contributions from the APEX measurements, knowledge of VOC emissions from aircraft at idle power settings was still limited. VOC emissions vary as a function of engine state, environmental variables (especially ambient temperature), and engine type. To quantify airport HAP emissions in the context of an airport inventory, data are needed on HAP emission rates as a function of low power settings and ambient conditions. This research project is aimed at arming airport operators with a simple methodology for improving estimates of HAP Figure I-1. UHC emissions during a landing/ species in the airport operational context. The test program takeoff cycle.