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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2012. Measurement of Gaseous HAP Emissions from Idling Aircraft as a Function of Engine and Ambient Conditions. Washington, DC: The National Academies Press. doi: 10.17226/13655.
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Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2012. Measurement of Gaseous HAP Emissions from Idling Aircraft as a Function of Engine and Ambient Conditions. Washington, DC: The National Academies Press. doi: 10.17226/13655.
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1 S u m m a r y This project characterized the dependence of gaseous hazardous air pollutants (HAP) and other partially combusted fuel emissions from aircraft on ambient and near-idle engine conditions, including temperature and engine thrust setting. The measurement work focused on characterization of on-wing CFM56 engines installed on commercial aircraft and operated according to airline practice. This project also developed a simple empirical frame- work (based on measurement data collected on variants of the CFM56 engine) that can be used in emissions scenario analysis. Three measurement campaigns were conducted at Chicago Midway Regional Airport (MDW), Chicago O’Hare International Airport (ORD), and Dallas Love Airport (DAL) in 2009 and 2010. Measurement tests focused on the CFM56-7B24 and -3B1 engine types. A single V2527 engine and a PW4090 engine were also characterized. The temperatures during these tests ranged from -8°C to 25°C (18°F to 77°F). Engine conditions examined ranged from the minimum fuel flow rates used at airports (ground idle with zero bleed air demand) to the International Civil Aviation Organization (ICAO) certification thrust setting for taxi/idle (7% of maximum rated thrust). Exhaust from the measured aircraft engines was collected using state-of-the-art probe/sampling schemes and analyzed using instrumentation housed in a mobile laboratory. Speciated measurements of HAP compounds such as formaldehyde, benzene, and 1,3-butadiene were measured using high-time-response, research grade instrumentation. The main HAP emissions from aircraft engines are volatile organic compounds (VOCs), with the important HAPs being formaldehyde, benzene, and acetaldehyde. Both the fuel-based emission indices (grams of benzene per kilogram of fuel combusted) and emission rates (grams of benzene per second) of VOCs increase with decreases in ambient temperature and fuel flow rate. A major accomplishment of this project’s research is the formulation of a simple model (currently only applicable to selected variants of the CFM56 engine type) that outputs the relative change in VOC emission index compared with ICAO’s reference temperature condition (15°C). Findings The findings of this project are summarized as follows: 1. Temperature dependence: VOC emission indices are approximately twice as high under cold conditions (-8°C to 0°C) as they are at 15°C for the CFM56-7B24. Measurement of Gaseous HAP Emissions from Idling Aircraft as a Function of Engine and Ambient Conditions

22. Fuel flow rate dependence: For the engine states that are likely to be most representative of the operational aircraft taxiway engine state, the VOC emission indices for the CFM56-7B24 are approximately 40% greater than the ICAO certification engine state (7% thrust). 3. VOC speciation: The composition profile of the exhaust is constant. The ratios of individual VOCs (e.g., formaldehyde to 1,3-butadiene) remain constant over all thrust settings and temperatures encountered. The first two findings are thus expected to be applicable to all VOCs measured, with the exception that there is a dependence of benzene emissions on fuel aromatic content. Implications for Airport Operators The data collected and analyzed in this project can be used by airport operators to improve the accuracy of taxiway emissions for selected aircraft engine types. Inventory assessment, whether performed for regulatory needs or not, can help prioritize sources that may require mitigation. Organic gas emissions can influence air quality by direct toxicological influence (HAP compounds specifically) by accelerating the production of ozone (a criteria pollutant) and by contributing to secondary organic aerosol (with its visibility and potential health consequences). This work has characterized the dependence of VOC engine emissions on ambient tem- perature under taxiway and terminal area operational engine states. These results can also be used to inform decisions on minimizing HAP emissions. The simple model developed in this work can be used to quantify the emissions benefits from proposed changes in airport operations. The results from this project can be used to relate the inventory of HAP emissions from aircraft engines during routine airport operation to emissions mitigation strategies such as single-engine taxiing or temporary engine shutdown practice during taxi delays.

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TRB’s Airport Cooperative Research Program (ACRP) Report 63: Measurement of Gaseous HAP Emissions from Idling Aircraft as a Function of Engine and Ambient Conditions is designed to help improve the assessment of hazardous air pollutants (HAP) emissions at airports based on specific aircraft operating parameters and changes in ambient conditions.

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