9.10 Commercial Aircraft, Jet

Categories 1115, 1119, 1123, 1127, 1128, and 1129

9.10.1 Introduction

Considered in these categories are criteria pollutant (particulate, organic, NOx, SOx, and CO) emissions from commercial jet aircraft during their operation 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 aircraft. The major passenger aircraft are further broken down into sub-groups of short-ranged, medium-ranged, long-ranged, and seasonal/chartered aircraft. Both the major passenger and cargo aircraft categories are primarily jet aircraft.

Category Description
1115 Major Passenger Aircraft (SFO)
1119 Major Passenger Aircraft (OAK)
1123 Major Passenger Aircraft (SJC)
1127 Cargo Aircraft (SFO)
1128 Cargo Aircraft (OAK)
1129 Cargo Aircraft (SJC)

The basic types of gas turbine engines used for commercial jet aircraft propulsion are turbojet and turbofan engines:

  1. In a turbojet engine, large quantities of air enter the engine in the front and then compressed and squeezed by the compressor before passing into the combustion chamber. This resulting mixture of fuel and air is then burned to produce hot, expanding gases. These high velocity gases pass through a turbine that is used to drive the compressor. The remaining energy in the air stream is used for aircraft propulsion. The earlier centrifugal types of compressors used in turbojets were reliable and simple, but the amount of thrust produced was relatively low because the compression ratio is not very high. These engines were also noisy and had poor fuel economy. Therefore, the quieter and more fuel-efficient turbofan engines rapidly replaced these engines.

  2. Turbofan aircraft engines power most airline transports in service today. The air entering the forward end of the engine is compressed and then heated by burning fuel in the combustion chamber. The turbofan engine uses its fan to accelerate additional air around the outside of the engine (called the bypass flow) to produce a larger, slower-moving exhaust mass for efficient high subsonic propulsion.

9.10.2 Methodology

Categories 1115, 1119, 1123, 1127, 1128, and 1129 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 the landing and takeoff, or 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 2300 feet on landing and subsequent takeoff to reach the 2300-foot altitude. The 2300-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 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

  3. Taxi/idle-out

  4. Take-off

  5. 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 Bank367, the Intergovernmental Panel on Climate Change (IPCC)368, the FAA’s Aviation Environmental Design Tool (AEDT)369, the U.S. Environmental Protection Agency (EPA) document AP-42370, and the California Air Resources Board (CARB)371.

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 total organic gas (TOG) emitted from these emission categories is considered to be 99.11 percent reactive organic gas (ROG). The PM10 and PM2.5 to PM ratios (PM10/PM and PM2.5/PM) are 0.976 and 0.967 respectively. The ROG and PM speciation information is in accordance with the CARB 2015 speciation data for Jet Exhaust372.

(f) Sample Calculations

TOG emissions for B747-300 (long-range aircraft):

\[ \text{TOG Emissions } = 4,878\ \text{LTO/yr} \times 24.56\ \text{lb/LTO} \div 365\ \text{day/yr} \div \text{2000 lb/ton} = 0.164\ \text{ton/day}\ \text{TOG} \]

9.10.3 Changes in Methodology

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

9.10.4 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.

9.10.6 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.

9.10.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Update: November 06, 2023

9.10.8 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 28]. http://ww2.arb.ca.gov/homepage↩︎

  6. California Air Resources Board Speciation Data. [accessed 2022 Dec 27]. https://ww2.arb.ca.gov/speciation-profiles-used-carb-modeling↩︎