Aircraft emissions represent approximately 90 percent of total airport emissions, and a majority of carbon monoxide (CO) and hydrocarbon (THC) emissions are produced during the taxi/idle phase of operation. Airports are often required to analyze emissions to gauge the impact of new projects that could result in operational changes or increased activity. It is therefore important that the impact of aircraft be accurately estimated for regional air quality State Implementation Plans and/or National Environmental Policy Act (NEPA) documents. The International Civil Aviation Organization (ICAO) tabulates engine emissions performance in its Emissions Databank and defines idle at 7 percent of rated thrust. Airports are required to use the Emission Dispersion Modeling System (EDMS) and Aviation Environmental Design Tool (AEDT), which use ICAO emissions indices to represent engine idle. In practice, however, most aircraft engines idle at fuel flow rates less than the ICAO definition for engine idle. It has been shown through both modeling and measurements that emissions of CO and THC increase as the fuel flow rate drops below the rate defined by the 7 percent thrust rating. Research is needed to develop an improved methodology to estimate aircraft engine emissions during the taxi/idle phase of operation.
The objectives of this research are to develop: (1) a prioritized list of potential improvements to EDMS/AEDT that will increase their predictive accuracy for estimating commercial jet aircraft emissions during the taxi/idle phase of operation and (2) detailed documentation of select near-term, high-priority improvements. The research should include:
1. A literature review;
2. A review of EDMS/AEDT modeling inputs, assumptions, algorithms, database coverage, and outputs relative to estimating commercial jet aircraft emissions during the taxi/idle phase of operation, and an assessment of the models’ ability to capture operational practice and predictive accuracy;
3. An analysis of actual, in-service engine performance data compared to taxi/idle assumptions in EDMS/AEDT. (See Special Note A);
4. An evaluation of the implications of model inaccuracies relative to airport emissions inventories;
5. A prioritized list of potential EDMS/AEDT improvements that would result in a more accurate methodology for estimating emissions during the taxi/idle phase that would consider (but not be limited to):
· Converting fuel flow data into emissions factors during taxi/idle conditions for representative engine/aircraft types,
· Incorporating ambient conditions (e.g., temperature),
· Improving representation of actual operational practice (e.g., single-engine taxi, e-taxi) and specific airport characteristics;
6. Detailed documentation of recommended near-term, high-priority improvements to EDMS/AEDT that would result in more accurate predictions of emissions during the taxi/idle phase (see Special Note B);
7. Stakeholder outreach to obtain feedback on the detailed documentation of recommended near-term, high-priority improvements to EDMS/AEDT (see Special Note C); and
8. A description of the steps needed for implementation of the model improvements.