Research Projects

In-Flight Aircraft Emissions Tracer Study

The emissions dispersion model used by airports for regulatory purposes does not account for aircraft-specific exhaust emissions transport and may be under- or over-estimating ground-level concentrations. Tracer studies for aircraft do not exist as they do for vehicles and are needed to evaluate newly developed dispersion models designed to better estimate the transport of aircraft exhaust emissions during low-altitude flight.

Background (Describe the current situation or problem in the industry, and how your idea would address it.)

Air quality assessments are periodically needed at airports to estimate impacts due to proposed changes in airport operations or flight plans (e.g., adding a runway, increasing flight operations, etc.) in order to comply with National Environmental Policy Act and Clean Air Act requirements. Dispersion models using the best available science may be underestimating pollutant levels under flight paths and overestimating pollutant levels further away (laterally), because they do not account for exhaust emissions entrainment from aircraft due to the wingtip vortices that are generated during flight. These vortices may lead to more efficient transport of aircraft emissions to the ground during low-altitude flight operations (i.e., during landings and take-offs). Current models may not accurately predict the location or level of peak concentrations, possibly leading airports into conducting unnecessary (and costly) emissions offsets or other requirements. While new dispersion models specific to aircraft emissions are being developed, currently no comprehensive tracer, or tracer-like data set exists to evaluate these dispersion models against. Without an evaluation data set, there is a risk that newly developed models may still inaccurately estimate the spatial distribution of aircraft emissions. This research proposes to create a public data set of measured exhaust emissions from in-flight aircraft upon landing and take-off at an airport with minimal influence from external pollution sources.

Objective (What is the desired product or result that will help the airport industry?)

The objective of this research is to create a public data set of a measured tracer or tracer-proxy (e.g., ultrafine particle (100 nanometers diameter or less) emissions) based on the current fleet of commercial aircraft flying in the US as measured at an airport located far from other pollution sources (i.e., major cities, highways, point sources). Similar to other tracer studies, an array of ground-level monitors would be positioned both directly under the flight path as well as laterally (relative to the flight path) at varying distances away from the airport and flight path. Measurements would be conducted under various meteorological conditions (i.e., wind speeds and direction) at high temporal resolution (e.g., 1-minute averaging). An accompanying report would detail all on-site measurements (meteorological conditions, pollutant concentrations) as well as relevant aircraft details (e.g., aircraft type, weight, flight mode – landing or take-off), and provide suggestions for data stratifications when conducting model evaluations. The data set produced from this research would be measurements of aircraft-specific emissions transport at multiple ground-level receptors (measured simultaneously) for which new dispersion model estimates can be evaluated against. This type of data set is critical when attempting to build a dispersion model for regulatory use as a potential alternative to AERMOD.

Approach (Describe in general terms the steps you think are needed to achieve the objective.)

The following steps would be used to conduct the research:
- Identify an airport with minimal impact from other emission sources that accommodates a range of commercial aircraft (e.g., Denver International Airport or Jackson Hole Airport).
- Design monitoring array ground layout.
- Install pollutant/tracer monitoring array and on-site meteorology station.
- Measure aircraft emissions, meteorology, and acquire flight position data and aircraft details.
- Compile data into public data set.
- Write report documenting measurement details, assessing data quality, and summarizing general data results.

Cost Estimate and Backup (Provide a cost estimate and support for how you arrived at the estimate.)

The following cost estimate was based on prior experience with measurement studies of ultrafine particles.
Airport/receptor scouting: $25,000
Array/equipment design, acquisition & installation: $325,000
Measurements (including setup): $100,000
Final dataset & report development: $100,000
Total: $550,000

Related Research - List related ACRP and other industry research; describe gaps (see link to Research Roadmaps above), and describe how your idea would address these gaps. This is a critical element of a synthesis topic submission.

ACRP Research Report 179 (2017) – "Dispersion Modeling Guidance at Airports Addressing Local Air Quality Health Concerns" – details an intercomparison of four different dispersion models, including AERMOD. The report points to a need for dispersion models to incorporate aircraft engine exhaust plume rise and to better understand the effects on plume rise due to aircraft downwash. This proposed project would result in the creation of a detailed public data set of a measured aircraft exhaust tracer/pollutant, which would inherently include aircraft plume rise and downwash effects, for public use to assist with the development and intercomparison of new dispersion models for airports.

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Idea No. 305