9.12 General Aviation, Jet

Categories 441 - 444, 446 - 453, and 455

9.12.1 Introduction

Considered in these categories are criteria pollutant emissions (particulate, organic, NOx, SOx, and CO) from gas turbine (jet) engines from general aviation aircraft during their operations at various airports in the San Francisco Bay Area.

Category Description
441 General, Jet (Livermore)
442 General, Jet (Hayward)
443 General, Jet (Oakland North)
444 General, Jet (Buchanan Field)
446 General, Jet (Gnoss Field)
447 General, Jet (Napa County)
448 General, Jet (Half Moon Bay)
449 General, Jet (San Carlos)
450 General, Jet (San Francisco International)
451 General, Jet (Reid-Hillview)
452 General, Jet (San Jose International)
453 General, Jet (South County)
455 General, Jet (Sonoma County)

These general aviation jet aircraft operate from both, large commercial and smaller county airports. The gas turbine engine consists of a compressor, a combustion chamber and a turbine. Air entering the forward end of the engine is compressed and then heated by burning fuel in the combustion chamber. The engine uses its fan to accelerate additional air around the outside of the engine producing exhaust gases for efficient propulsion.

9.12.2 Methodology

Categories 441 - 444, 446 - 453, and 455 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.

Normal flight and ground operation modes of the aircraft constitutes the landing/takeoff (LTO) cycle. For criteria pollutant emission inventory, the aircraft LTO cycle is divided into five segments or operational “modes” and categorized by:

  1. Startup, idle and taxi out,
  2. Takeoff,
  3. Climb out to about 2,300 feet–this height is considered the average mixing depth in the Bay Area and assumed inversion height, wherein aircraft exhaust emissions are released below it,
  4. Descent/approach from 2,300 feet, touch down, and landing run,
  5. Taxi in, idle and shutdown.

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 operations and fleet mix were obtained from the airports, the Federal Aviation Administration (FAA), and the Metropolitan Traffic Commission (MTC).

(b) County Distribution / Fractions

The county location of each airport and aircraft activity was used to distribute emissions into each county . For example, San Francisco International Airport (SFO) is in San Mateo County, Oakland International Airport (OAK) is in Alameda County, San Jose International Airport (SJC) is in Santa Clara County, and about a dozen smaller airports with jet aircraft activities in their corresponding counties in the Bay Area.

(c) Emission Factors

The landing and take-off (LTO) cycle has its equivalent operating time-in-mode (TIM) which is the time for a particular aircraft to go through each of the five modes. Composite modal emission rates (MER) for various types of aircraft engines in general aviation use were developed based on information from the International Civil Aviation Organization (ICAO) Aircraft Engine Emissions Data Bank381, the Intergovernmental Panel on Climate Change (IPCC)382, the FAA’s Aviation Environmental Design Tool (AEDT)383, the U.S. Environmental Protection Agency (EPA) document AP-42384, and the California Air Resources Board (CARB)385.

Emission rates vary according to engine type and operating mode. Emission factors for a 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.

(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 CARB386 and the US Environmental Protection Agency387. For this category or group of categories, ROG constitutes 89.19% 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 CARB388 or the US Environmental Protection Agency. For this category or group of categories, PM2.5 constitutes 96.7% of total PM and PM10 constitutes 97.6% of total PM. The Air District staff routinely review speciation profiles and may update ratios as needed for improving emissions estimates.

(f) Sample Calculations

TOG emissions for Cessna Citation Jet:

\[ 7,942\ \text{LTO/yr} \times 1.82\ \text{lb/LTO} \div 365\ \text{day/yr} \div \text{2000 lb/ton} = 0.02\ \text{ton/day}\ \text{TOG} \]

9.12.3 Changes in Methodology

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

9.12.4 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 will result in reduced emissions from general aviation sector.

9.12.6 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 and throttle settings will also help improve emission factors, therefore, an improved and accurate emissions inventory.

9.12.7 Contact

Author: Sukarn Claire

Reviewer: Michael Nguyen

Last Update: November 06, 2023

9.12.8 References & Footnotes

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

  2. The Intergovernmental Panel on Climate Change (IPCC). https://www.ipcc.ch/↩︎

  3. The FAA’s Aviation Environmental Design Tool (AEDT). 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. 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↩︎

  9. Metropolitan Transportation Commission (MTC) Publications. https://mtc.ca.gov/tools-resources/mtcabag-library↩︎