3.3 Airports: aircraft-related emissions
The EPA estimated emissions related to aircraft activity for all known U.S. airports, including seaplane ports and heliports, in the 50 states, Puerto Rico, and U.S. Virgin Islands. Approximately 20,000 individual airports are geographically located by latitude/longitude and stored in the NEI as point sources. As part of the development process, S/L/T agencies had the opportunity to provide both activity data as well as emissions to the NEI. When activity data on landings and take-offs were provided by S/L/Ts, the EPA used that data to calculate the EPA’s emissions estimates.
3.3.1 Sector Description
The aircraft sector includes all aircraft types used for public, private, and military purposes. This includes four types of aircraft: (1) commercial, (2) air taxis (AT), (3) general aviation (GA), and (4) military. A critical detail about the aircraft is whether each aircraft is turbine- or piston-driven, which allows the emissions estimation model to assign the fuel used, jet fuel or aviation gas, respectively. The fraction of turbine- and piston-driven aircraft is either collected or assumed for all aircraft types.
Commercial aircraft include those used for transporting passengers, freight, or both. Commercial aircraft tend to be larger aircraft powered with jet engines. Air taxis carry passengers, freight, or both, but usually are smaller aircraft and operate on a more limited basis than commercial aircraft. General aviation includes most other aircraft used for recreational flying and personal transportation. Finally, military aircraft are associated with military purposes, and they sometimes have activity at non-military airports.
The national AT and GA fleets include both jet- and piston-powered aircraft. Most of the AT and GA fleets are made up of larger piston-powered aircraft, though smaller business jets can also be found in these categories. Military aircraft cover a wide range of aircraft types such as training aircraft, fighter jets, helicopters, and jet- and piston-powered planes of varying sizes.
The NEI also includes emission estimates for aircraft auxiliary power units (APUs) and aircraft ground support equipment (GSE) typically found at airports, such as aircraft refueling vehicles, baggage handling vehicles and equipment, aircraft towing vehicles, and passenger buses. These APUs and GSE are located at the airport facilities as point sources along with the aircraft exhaust emissions.
The emissions associated with airport activities are attributed to the following sources with associated source classification codes (SCC):
- Commercial aviation (SCC: 2275020000)
- Air taxis
- Piston driven (SCC: 2275060011)
- Turbine driven (SCC: 2275060012)
- General aviation
- Piston driven (SCC: 2275050011)
- Turbine driven (SCC: 2275050012)
- Military (SCC: 2275001000)
- Auxiliary Power Units (SCC: 2275070000)
- Ground Support Equipment
- Diesel-fueled (SCC: 2270008005)
- Gasoline-fueled (SCC: 2265008005).
3.3.2 Sources of aircraft emissions estimates
Aircraft exhaust, GSE, and APU emissions estimates are associated with aircraft’s landing and takeoff (LTO) cycle. LTO data were available from both S/L/T agencies and FAA databases. For airports where the available LTO included detailed aircraft-specific make and model information (e.g., Boeing 747-200 series), we used the FAA’s Aviation Environmental Design Tool (AEDT) to estimate CAP and HAP emissions. The EPA first used the AEDT model for the 2017 NEI. Previous NEIs, including 2008 and 2011, used the FAA’s previous model, Emissions and Dispersion Modeling System (EDMS). Therefore, comparisons of aircraft emissions output may be a function of model revisions, rather than an actual trend in emissions. If such detailed data were not available, generic emission factors were used in combination with estimates of activity by different aircraft types (i.e., air taxis, general aviation, and military aircraft) to calculate emissions. The emissions factors (EFs) used, as well as the complete methodology for estimating aircraft exhaust from LTOs is in the aircraft documentation available in the document “2023NEI Aviation Documentation” on the 2023 Supporting data FTP site. For 2023 NEI, only Texas and Georgia submitted aircraft emissions. Georgia submitted emissions for just the Hartsfield-Jackson Atlanta International Airport. Additionally, eight states (Connecticut, Delaware, Georgia, Maryland, Maine, North Carolina, Virginia, and Washington), the District of Columbia, and one local program (Maricopa County Air Quality Department) provided revised operations data through the state review process.
In addition to airport facility point, the EPA also estimated in-flight lead (Pb - from aviation gas) emissions and allocated those emissions to counties in the nonpoint inventory. For lead only, the NEI currently accounts for lead emitted in-flight, at altitudes above the landing and takeoff cycle. This calculation is derived by calculating the total amount lead in the national estimate of leaded fuel used (aviation gas), and then subtracting the lead accounted for in the LTO cycle. The remainder is assumed to be the in-flight lead emissions (Table 3.4). That value is distributed to states by the ratio of LTOs in the state from piston aircraft engine SCCs. They are stored in a single county estimate, with county code ending in **777 to indicate ‘multiple/portable’ location.
| 2011 | 2014 | 2017 | 2020 | 2023 | |
|---|---|---|---|---|---|
| Fuel Consumption (Gallons) | 217500000 | 210000000 | 209000000 | 193000000 | 224979700 |
| Total emissions in fuel (tons emissions) | 483 | 466 | 464 | 428 | 499 |
| Accounted for in LTO (tons emissions) | 245 | 228 | 221 | 176 | 245 |
| Remainder in Flight (tons emissions) | 238 | 238 (A) | 243 | 252 | 254 |
A. The value erroneously used for 2014 in-flight lead emissions: 228 tons. The percent difference caused by the error: 4.20%.
A summary of state-level in-flight lead estimates “2023-lead-calculations-by-state-final.xlsx” can be found on the 2023 Supporting data FTP site.