9.11 Commercial Aircraft, Piston

Categories 1130, 1131, and 1132

9.11.1 Introduction

Considered in these categories are criteria pollutant emissions (particulate, organic, NOx, SOx, and CO) and greenhouse gas emissions (CO2, CH4, and N2O) from commercial piston aircraft during their operations at the three major airports in the Bay Area, namely, San Francisco International (SFO), Oakland International (OAK), and San Jose International (SJC). A classification system for commercial aircraft was formulated consisting of major passenger, cargo, and commuter/air taxi. The commuter/taxi class is primarily of the piston type aircraft.

Category Description
1130 Commuter/Taxi Aircraft (SFO)
1131 Commuter/Taxi Aircraft (OAK)
1132 Commuter/Taxi Aircraft (SJC)

In the piston engine, the basic element is the combustion chamber. Mixtures of fuel and air are burned in this chamber from which energy is extracted by)a piston and crank mechanism driving a propeller. The turboprop engine has a propeller turned through a system of gears from a gas turbine system; it usually delivers more thrust–up to medium-high subsonic airspeeds. The majority of the commuter/taxi aircraft use this turboprop engine propulsion.

9.11.2 Methodology

Categories 1130, 1131 and 1132 are considered an area source category since they cover facilities / emission sources that are not directly permitted by the District, and hence not systematically cataloged. Emissions for area source categories are determined using the formula:

Current Year Emissions = Base Year Emission X Growth Profile, and,

Base Year Emission = Throughput X Control Factor X Emission Factor

where,

  • throughput or activity data for applicable base year(s) is determined using a top-down approach (e.g. state-, national-level data);
  • emission factor is derived from general literature, specific literature and reports, and/or source testing results provided by Air District staff;
  • control factor (if applicable) is determined by District and state rules and regulations in effect;
  • and, historical backcasting and forecasting of emissions is based on growth profiles as outlined in the Trends section of this chapter

More details on throughput, county distribution, emission factors and controls is provided in the following subsections.

The pollutants emitted by an aircraft during take-off and landing operations are dependent on the emission rates and the duration of these operations. The emission rates are dependent upon the type of engine and its size or power rating. An aircraft operational cycle includes landing and takeoff (LTO) cycle. For criteria pollutant emission inventory, an LTO cycle includes all normal operational modes performed by an aircraft between its descent from an altitude of about 2,300 feet on landing, and subsequent takeoff to reach the 2,300-foot altitude. The 2,300-foot limit is a reasonable approximation to the meteorological mixing depth over the Bay Area metropolitan areas. The term “operation” is used by the Federal Aviation Administration (FAA) to describe either a landing or a take-off cycle. Therefore, two operations make one LTO cycle.

For criteria pollutant emission calculations, the aircraft LTO cycle is divided into five segments or operational “modes” and categorized by:

  1. Landing approach (descent from about 2,300 ft. to touch down), 2. Taxi/idle-in

  2. Taxi/idle-out

  3. Take-off

  4. Climb out (ascent from lift-off to about 2,300 ft.)

The emissions are based on the time of operation in each mode and the emission rates of the engines. The time in the landing approach and climb out modes are assumed to be 3.02 minutes and 1.55 minutes, respectively. Take-off time of 0.95 minute (including 0.25 minute for reverse thrust) is fairly standard for commercial aircraft and represents the time for initial climb from ground level to about 500 feet. The time in taxi/idle mode usually varies with airports.

For greenhouse gas (GHG) emission inventory, in addition to LTO cycle explained above, the aircraft landing approach and climb out modes above 2,300 feet elevation and aircraft cruise mode in the District’s air space is also included.

(a) Activity Data / Throughput

The information on number of aircraft operations and fleet mix was obtained from the three major commercial airports in the Bay Area and the Federal Aviation Administration (FAA).

(b) County Distribution / Fractions

The county location of each airport was used to distribute emissions into each county, where SFO is in San Mateo County; OAK is in Alameda County, and SJC in Santa Clara County.

(c) Emission Factors

The modal emission rate information and the fuel specific greenhouse gas emission coefficients for aircraft engines in commercial use were obtained from the International Civil Aviation Organization (ICAO) Aircraft Engine Emissions Data Bank373, the Intergovernmental Panel on Climate Change (IPCC)374, the FAA’s Aviation Environmental Design Tool (AEDT) 375, the U.S. Environmental Protection Agency (EPA) document AP-42376, and the California Air Resources Board (CARB)377.

Emission rates vary according to engine type and operating mode. Emission factors for specific aircraft were estimated by the equation:

\[ \text{EMF} = \text{N} \times \sum{\left( v_e / v_t \right)_{m,p}} \times \text{TIM} \] where:

  • \(\text{EMF}\) = emission factor (lb/LTO)
  • \(\text{N}\) = number of engines
  • \(\left( v_e / v_t \right)_{m,p}\) = engine emission rates (lb/hr) at mode \(m\), pollutant \(p\); and
  • \(\text{TIM}\) = time in mode \(m\) (hr).

(d) Control Factors

No emission controls have been implemented by the Air District for these categories. Federal airport noise regulations, over the years, have forced changes to the commercial aircraft fleet resulting in replacement of loud and dirtier engines with newer, quieter, and cleaner burning engines.

(e) Speciation

The ROG/TOG ratios applied to this category or this group of related categories are based on an Air District internal speciation profile. Multiple data sources have been used for developing speciation profiles, such as Air District-approved source tests, TOG speciation ratios used by other regional air quality agencies, and relevant literature including latest speciation profiles developed by CARB378 and the US Environmental Protection Agency379. For this category or group of categories, ROG constitutes 99% of TOG. Further assessment and improvement of ROG/ TOG speciation profiles has been planned in future inventory updates.

The PM2.5/PM and the PM10/PM ratios applied to this category or this group of related categories are based on an Air District internal speciation profile. Multiple data sources have been used for developing speciation profiles, such as Air District-approved source tests, PM speciation ratios used by other regional air quality agencies, and other relevant literature. These ratios are not necessarily consistent with the latest speciation profiles developed by CARB380 or the US Environmental Protection Agency. For this category or group of categories, PM2.5 constitutes 94% of total PM and PM10 constitutes 99% of total PM. The Air District staff routinely review speciation profiles and may update ratios as needed for improving emissions estimates.

(f) Emission Calculations

TOG emissions per landing and take-off (LTO):

\[ \ \text{LTOs/yr} \times \ \text{lb/LTO} \div 365\ \text{day/yr} \div \text{2000 lb/ton} = \ \text{ton/day}\ \text{TOG} \]

TOG emissions per LTO for a Boeing 737-max aircraft with 12,000 LTOs per year:

TOG Emissions = (12,000 LTOs/yr x 0.95 lb/LTO) ÷365 day/yr÷2000 lb/ton = 0.0156 ton/day

9.11.3 Changes in Methodology

No changes to methodology were made in this version of the base year emissions inventory.

9.11.4 Emissions

A summary of emissions by category, county, and year are available via the associated data dashboard for this inventory publication.

The continuing effort in aircraft improvement, development of newer engine technology and their phasing in have resulted in reduced emissions. There is a continuing trend in the use of larger aircraft thereby increasing the passenger to LTO ratio. This will reduce the number of LTOs and consequently, lower emissions.

9.11.6 Uncertainties

The aircraft landing and take-off (LTO) cycle emission factors can be improved if more accurate local airport data was available for the aircraft operational modes such as, Landing approach, Taxi/idle-in, Taxi/idle-out, Take-off, and Climb-out. Use of actual verses typical or standard data, such as, time in each mode, throttle settings, frequency of less than all-engine taxi operations and better accounting of emissions from aircraft auxiliary power units will also help improve emissions inventory.

9.11.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Updated: November 06, 2023

9.11.8 References & Footnotes

  1. The International Civil Aviation Organization (ICAO). [accessed 2022 Dec 10]. https://www.easa.europa.eu/domains/environment/icao-aircraft-engine-emissions-databank↩︎

  2. The Intergovernmental Panel on Climate Change (IPCC). [accessed 2022 Dec 15]. https://www.ipcc.ch/↩︎

  3. The FAA’s Aviation Environmental Design Tool (AEDT). [accessed 2022 Dec 12]. https://aedt.faa.gov/↩︎

  4. EPA. 1995. AP-42. Compilation of Air Pollutant Emissions Factors. https://www.epa.gov/regulations-emissions-vehicles-and-engines/regulations-nitrogen-oxide-emissions-aircraft↩︎

  5. The California Air Resources Board. [accessed 2022 Dec 27]. http://ww2.arb.ca.gov/homepage↩︎

  6. CARB. 2022. ORGPROF. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎

  7. U.S. EPA. 2022. SPECIATE. https://www.epa.gov/air-emissions-modeling/speciate↩︎

  8. CARB. 2022. PMSIZE. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎