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2. 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.
