9.15 Military Aircraft, Piston

Categories 682, 687, 694, 699, 702, 705, and 708

9.15.1 Introduction

These categories account for criteria pollutant emissions (particulate, organic, NOx, SOx, and CO) from piston engines from military aircraft operations at various air bases and naval fields or airports in the Bay Area where military operations exist.

Category Description
682 Military, Piston (Alameda NAS)
687 Military, Piston (Moffett Field)
694 Military, Piston (Travis AFB)
699 Military, Piston (SFO)
702 Military, Piston (OAK)
705 Military, Piston (SJC)
708 Military, Piston (Hayward)

In the piston engine, the basic element is the combustion chamber in which the mixture of fuel and air are burned and from which energy is extracted by a piston and crank mechanism driving a propeller.

9.15.2 Methodology

Categories 682, 687, 694, 699, 702, 705, and 708 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 LTO cycle is grouped into five modes, which is equivalent to two operations in an airport activity. These include:

  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 about 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

Number of aircraft flight operations in the Bay Area were obtained from the airports with military aircraft activity. Presently, the Travis Air Force Base is the only major military facility in the Bay Area with significant military aircraft operations. Share of military aircraft operations at the Bay Area commercial airports is much smaller compared to Travis Airforce Base.

(b) County Distribution / Fractions

The county location of each airbase, naval facility, or airport with military activities in the Bay Area was used to distribute emissions into each county.

(c) Emission Factors

The modal emission rate information and the fuel specific greenhouse gas emission coefficients for similar aircraft were obtained from the International Civil Aviation Organization (ICAO) Aircraft Engine Emissions Data Bank406, the Intergovernmental Panel on Climate Change (IPCC)407, the FAA’s Aviation Environmental Design Tool (AEDT)408, the U.S. Environmental Protection Agency (EPA) document AP-42409, and the California Air Resources Board (CARB)410.

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

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

(d) Control Factors

No emission controls have been implemented by the Air District for these categories. In general, Federal airport noise regulations, over the years, have forced changes in aircraft industry, 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 CARB411 and the US Environmental Protection Agency412. For this category or group of categories, ROG constitutes 89.69% 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 CARB413 or the US Environmental Protection Agency. For this category or group of categories, PM2.5 constitutes 99.4% of total PM and PM10 constitutes 99.2% 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 per landing and take-off (LTO):

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

9.15.3 Changes in Methodology

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

9.15.4 Emissions

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

In general, continuing effort in aircraft improvement, development of newer engine technology and their phasing in have resulted in reduced emissions. Low military aircraft activity results in negligible emissions for a majority of pollutants at the Bay Area commercial airports.

9.15.6 Uncertainties

The aircraft landing and take-off (LTO) cycle emission factors can be improved if the data specific to the local airports 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.

9.15.7 Contact

Author: Sukarn Claire

Reviewer: Minh Nguyen

Last Update: November 06, 2023

9.15.8 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↩︎