2.2 Aviation

Category ID	Description	EIC
441	General Aviation - Jet Aircraft - Livermore	81081214000000
442	General Aviation - Jet Aircraft - Hayward	81081214000000
443	General Aviation - Jet Aircraft - Oakland North	81081214000000
444	General Aviation - Jet Aircraft - Buchanan Field	81081214000000
446	General Aviation - Jet Aircraft - Gnoss Field	81081214000000
447	General Aviation - Jet Aircraft - Napa County	81081214000000
448	General Aviation - Jet Aircraft - Half Moon Bay	81081214000000
449	General Aviation - Jet Aircraft - San Carlos	81081214000000
450	General Aviation - Jet Aircraft - San Francisco International	81081214000000
451	General Aviation - Jet Aircraft - Reid-Hillview	81081214000000
452	General Aviation - Jet Aircraft - San Jose International	81081214000000
453	General Aviation - Jet Aircraft - South County	81081214000000
455	General Aviation - Jet Aircraft - Sonoma County	81081214000000
456	General Aviation - Piston Aircraft - Livermore	81080411400000
463	General Aviation - Piston Aircraft - Hayward	81080411400000
475	General Aviation - Piston Aircraft - Oakland North	81080411400000
489	General Aviation - Piston Aircraft - Buchanan Field	81080411400000
496	General Aviation - Piston Aircraft - Gnoss Field	81080411400000
503	General Aviation - Piston Aircraft - Marin /Smith Ranch (Pvt)	81080411400000
505	General Aviation - Piston Aircraft - Parrett/Angwin	81080411400000
507	General Aviation - Piston Aircraft - Calistoga Airpark (Pvt)	81080411400000
510	General Aviation - Piston Aircraft - Inglenook/Napa	81080411400000
511	General Aviation - Piston Aircraft - Napa County	81080411400000
520	General Aviation - Piston Aircraft - Half Moon Bay	81080411400000
527	General Aviation - Piston Aircraft - San Carlos	81080411400000
534	General Aviation - Piston Aircraft - San Francisco International	81080411400000
541	General Aviation - Piston Aircraft - Palo Alto	81080411400000
548	General Aviation - Piston Aircraft - Reid-Hillview	81080411400000
555	General Aviation - Piston Aircraft - San Jose International	81080411400000
562	General Aviation - Piston Aircraft - South County	81080411400000
593	General Aviation - Piston Aircraft - Travis Aero Club	81080411400000
597	General Aviation - Piston Aircraft - Sonoma County	81080411400000
615	General Aviation - Piston Aircraft - Petaluma Sky Ranch	81080411400000
619	General Aviation - Piston Aircraft - Santa Rosa Air Center	81080411400000
626	General Aviation - Piston Aircraft - Sonoma Valley/Schelville	81080411400000
632	General Aviation - Piston Aircraft - Sonoma SkyPark	81080411400000
639	Military Aircraft - Jet Aircraft - Alameda NAS	81080814000000
646	Military Aircraft - Jet Aircraft - Moffett Field	81080814000000
658	Military Aircraft - Jet Aircraft - Travis AFB	81080814000000
670	Military Aircraft - Jet Aircraft - San Francisco International	81080814000000
673	Military Aircraft - Jet Aircraft - Oakland International	81080814000000
676	Military Aircraft - Jet Aircraft - San Jose International	81080814000000
682	Military Aircraft - Piston Aircraft - Alameda NAS	81080011400000
687	Military Aircraft - Piston Aircraft - Moffett Field	81080011400000
694	Military Aircraft - Piston Aircraft - Travis AFB	81080011400000
699	Military Aircraft - Piston Aircraft - San Francisco International	81080011400000
702	Military Aircraft - Piston Aircraft - Oakland International	81080011400000
705	Military Aircraft - Piston Aircraft - San Jose International	81080011400000
711	Agricultural Aircraft - Piston Aircraft	81080611400000
1115	Commercial Aircraft - Major Passenger Aircraft - San Francisco International Airport	81081014000000
1119	Commercial Aircraft - Major Passenger Aircraft - Oakland International Airport	81081014000000
1123	Commercial Aircraft - Major Passenger Aircraft - San Jose International Airport	81081014000000
1127	Commercial Aircraft - Cargo Aircraft - San Francisco International Airport	81081014000000
1128	Commercial Aircraft - Cargo Aircraft - Oakland International Airport	81081014000000
1129	Commercial Aircraft - Cargo Aircraft - San Jose International Airport	81081014000000
1130	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Francisco International Airport	81081014000000
1131	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Oakland International Airport	81081014000000
1132	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Jose International Airport	81081014000000
1689	General Aviation - Piston Aircraft - Byron	81080411400000
2733	General Aviation - Jet Aircraft - Palo Alto	81081214000000
2734	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Napa County	81081014000000
2735	Military Aircraft - Jet Aircraft - Napa County	81080814000000
2736	Military Aircraft - Piston Aircraft - Napa County	81080011400000
2737	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Buchanan Field	81081014000000
2738	Military Aircraft - Jet Aircraft - Buchanan Field	81080814000000
2739	Military Aircraft - Piston Aircraft - Buchanan Field	81080011400000
2740	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Hayward	81081014000000
2741	Military Aircraft - Jet Aircraft - Hayward	81080814000000
2742	Military Aircraft - Piston Aircraft - Hayward	81080011400000
2743	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Livermore	81081014000000
2744	Military Aircraft - Jet Aircraft - Livermore	81080814000000
2745	Military Aircraft - Piston Aircraft - Livermore	81080011400000
2746	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Palo Alto	81081014000000
2747	Military Aircraft - Jet Aircraft - Palo Alto	81080814000000
2748	Military Aircraft - Piston Aircraft - Palo Alto	81080011400000
2749	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Reid-Hillview	81081014000000
2750	Military Aircraft - Jet Aircraft - Reid-Hillview	81080814000000
2751	Military Aircraft - Piston Aircraft - Reid-Hillview	81080011400000
2752	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Carlos	81081014000000
2753	Military Aircraft - Jet Aircraft - San Carlos	81080814000000
2754	Military Aircraft - Piston Aircraft - San Carlos	81080011400000
2755	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Sonoma County	81081014000000
2756	Military Aircraft - Jet Aircraft - Sonoma County	81080814000000
2757	Military Aircraft - Piston Aircraft - Sonoma County	81080011400000
2758	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Moffett Field	81081014000000
2759	General Aviation - Jet Aircraft - Moffett Field	81081214000000
2760	General Aviation - Piston Aircraft - Moffett Field	81080411400000

Introduction

This document outlines the methodology for estimating greenhouse gas (GHG) emissions from different types of end-use airline operations in the aviation subsector. The emissions inventory encompasses GHGs emitted in the fuel combustion exhaust from aircraft engines. The emissions are ascribed to different source categories based on unique combinations of airport, aircraft end-use type and aircraft engine-type. The combusted fuel is assumed to be either a form of kerosene (jet fuel or JP-8) or gasoline (aviation gasoline or avgas, mostly in smaller piston-engine aircraft). Combustion of these fuels produces GHGs, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Emissions from other airport ground-support equipment are addressed in the Off-Road Mobile Sources documentation.

There are a total of 84 active source categories with emissions in the base year 2023 under the Aviation subsector that are covered in this documentation. The scope of emissions coverage and source classification across this subsector is described below:

Commercial Air operations - Itinerant (traveling from place to place) revenue-generating airport operations that include both large air carrier operations (airplanes with more than 60 seats) plus air taxi and commuter operations (FAA, 2021).
Air Carrier Cargo operations – Commercial air carrier operations can be split between passenger travel and cargo transport. Cargo freighters for hire or compensation involve aircraft with a maximum payload capacity of more than 18,000 pounds.
Commuter Air Taxi (CAT) operations – Commercial itinerant airport operations performed using aircraft with 10 or more seats and having 60 or fewer seats to transport commuter (regional) passengers on short routes. These operations also include cargo transport for hire or compensation involving aircraft with a maximum payload capacity of 18,000 pounds or less.
General Aviation (GA) operations- Itinerant airport operations performed by all civil aircraft, except air carriers or commuter air taxis. These operations are, typically, carried out by aircraft with less than 10 passenger seats.
Agricultural Operations – Low-altitude small-aircraft flight operations to spray pesticides over agricultural crops.
Military operations - Itinerant airport operations performed by military aircraft that are typically owned and operated by United States Department of Air force (USDAF, 2024a)
Small, FAA ATC towered airports – These source categories include those operations occurring at airports with Federal Aviation Administration (FAA) approved air traffic controllers (ATC) and representing the sum of itinerant and local operations (short-duration operations beginning and ending at the same airport) within the General Aviation and Military designations. Some commuter air taxis operations may also occur at these airports, though commercial passenger and cargo operations are rare and virtually non-existent. In the San Francisco Bay Area (SFBA), there are eight airports under this operational designation:

Airport Code	Airport Name and/or City	County
APC	Napa	Napa
CCR	Buchanan Field, Concord	Contra Costa
HWD	Hayward	Alameda
LVK	Livermore	Alameda
PAO	Palo Alto	Santa Clara
RHV	Reid-Hillview, San Jose	Santa Clara
SQL	San Carlos	San Mateo
STS	Charles Schulz Sonoma County, Santa Rosa	Sonoma

Large, FAA ATC towered airports – These emissions source categories include itinerant operations of air carrier passenger and cargo aircraft, and commuter air taxis at three large commercial airports in the San Francisco Bay Area (SFBA):

Airport Code	Airport Name and/or City	County
OAK	Oakland San Francisco Bay International Airport	Alameda
SFO	San Francisco International Airport	San Francisco
SJC	San Jose International Airport	Santa Clara

These airports also include source categories representing the sum of itinerant and local operations within the General Aviation and Military operational classification occurring at these large commercial airports.

Small, non-towered airports – These operations occur at small city- and county-run airports that do not have an ATC. These source categories cover the sum of itinerant and local operations within the General Aviation operational classification and typically involve small piston-engine aircraft.

Airport Code	Airport Name and/or City	County
AFA	Smith Ranch, San Rafael	Marin
DVO	Gnoss Field, Novato	Marin
HAF	Half Moon Bay	San Mateo
C83	Byron	Contra Costa
E16	South County, San Martin	Santa Clara
O69	Petaluma	Sonoma
2O3	Parrett Angwin, Napa	Napa
0Q9	Sonoma Skypark	Sonoma
0Q3	Sonoma Valley	Sonoma

Military airports / federal airfields – These operations occur at USDAF, or federal government owned and operated air forces bases or airfields. The source categories cover the sum of itinerant and local operations within the Military operational designation. There are two military or joint civil-military airports in the SFBA

Airport Code	Airport name and/or City	County
NUQ	Moffett Federal Airfield	Santa Clara
SUU	Travis Air Force Base	Solano

NUQ airport is privately operated (since year 2015) and primarily hosts GA activity, with some ancillary military, coast guard and sheriff department airborne operations (NUQ, 2024).

Each emission source category at any airport represents one of two basic configuration types of aircraft engines:

Piston (reciprocating) engines: In a piston engine, an explosion of the fuel-air mixture drives a piston, which in turn makes a driveshaft turn. The driveshaft then turns the propeller. Most GA and civil aircraft run on piston engines. 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 air speeds.
Jet engines: In a turbine 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. The expansion of the hot gas drives a turbine, which drives another turbine that compresses air (for the burning chamber). On the same axis as the first turbine, a propeller is mounted. A majority of CAT operations, and virtually all military, commercial passenger and cargo aircraft operations are powered by jet engines. These aircraft operate at high subsonic speeds.

In California, thus far, air districts develop and submit their own aircraft emissions inventories to the California Air Resources Board (CARB). These inventories are often based on disparate data sources and growth projections. In 2024, CARB put in a major effort to develop a statewide aircraft emissions inventory estimation model referred to as the 2024 California Aircraft Emissions Inventory Model (CAI, 2024). This model is aimed at standardizing methodology across all Air Districts within the state, given that aircraft are mobile sources that frequently travel between air district jurisdictions. This inventory is expected to be foundational to the development of future State Implementation Plans (SIP) as well as aircraft and airport specific regulations and control strategies. As the inaugural version of this statewide emissions inventory is still in a public comment phase, the current iteration of the GHG inventory for the aviation subsector for the SFBA is based on the Bay Area Air Quality Management District (BAAQMD) Emissions Inventory team’s methodology (that is presented in this write-up). In future, the CARB inventory model will be used to derive the regional aviation subsector emissions inventory.

Methodology

This section describes how GHG emissions are estimated for various aircraft operational groups – Passenger and Cargo, CAT, GA, Military and Agricultural. All of the 84 source categories in this subsector are considered area source categories. Area source categories cover emission sources that are not directly permitted by the Air District, so emissions are not systematically or annually cataloged and/or reported. The methodology used to calculate emissions for the reported base year(s) for the aircraft source categories follows:

Base Year(s) Emissions_{county,pollutant}=

Activity Data × Emission Factor_pollutant × Control Factor_pollutant × Fraction_county× GWP_pollutant

Where:

Base Year: is a year for which activity / throughput data is available (or can be derived or estimated).
Activity Data: is the total regional throughput or activity data for applicable base year(s).
Emission Factor_pollutant: is a factor that allocates an amount of emissions, in mass, of a particular pollutant by unit of activity data.
Control Factor_pollutant : is a fractional ratio (between 0 and 1) that captures the estimated reduction in emissions as a result of Air District rules and regulations.
Fraction_county: is the fraction of total regional emissions (between 0 and 1) estimated to be allocated to a particular county.
GWP_pollutant is the Global Warming Potential of a particular GHG pollutant. The current version of the GHG emissions inventory incorporates the global warming potential (GWP) reported in the Fifth Assessment report of the Intergovernmental Panel for Climate Change (IPCC, 2014). The GWPs for the three principal GHGs are 1 for carbon dioxide (CO₂), 34 for methane (CH₄), and 298 for nitrous oxide (N₂O), when calculated on a 100-year basis with climate-carbon feedback included.

Once base year emissions are determined, historical backcasting and forecasting of emissions relative to the base year emissions are estimated using growth profiles as follows:

Current Year Emissions _county = Base Year(s) Emission _county × Growth Factor

Where:

Growth Factor: is a scaling factor that is used to derive historical emissions estimates for years for which activity data and/or emissions are not reported (or available), and to forecast emissions for future years, using surrogates that are representative of activity and/or emissions trends for a specific source category.

More details on activity data/throughput, county distribution, emission factors and controls are provided in the following subsections.

Activity Data / Throughput

The basic activity data for all aircraft operations has been established by the US Environmental Protection Agency as a Landing and Takeoff (LTO) cycle (USEPA, 1992). An emissions inventory for aircraft operations focuses on quantifying pollutants emitted in the vertical column of the air referred to as the ‘mixing layer’ from surface-level up to the bottom of the inversion layer, where any emissions released at any height are assumed to get well-mixed across the entire depth of the mixing layer. A single LTO is defined as a complete cycle of aircraft activity involving the movement of the airplane in and out of the mixing layer. This typically involves two aircraft operations – a take-off and a landing (in any order). Emissions occurring above the mixing zone are outside the zone of influence of the SFBA and not considered as being within the jurisdiction of the Air District. These are the individual phases contained in an LTO cycle as defined by the USDAF (USDAF, 2024a). The USDAF utilizes phase-specific information to derive emissions for each aircraft model’s complete LTO cycle:

Taxi-out / Idle-out: The operational phase from engine startup to takeoff where engine is in idle power mode.
Takeoff: This phase is characterized by full engine thrust for the aircraft to reach 500 feet (ft) above ground level (AGL).
Climb Out: This phase includes the initial aircraft ascent from 500 ft AGL until the aircraft exits the mixing zone (default is 3,000 ft AGL), when the engine power mode is typically at intermediate levels.
Approach: This phase represents the aircraft’s return descent from when the aircraft enters the mixing zone to 0 ft AGL (touchdown). The engine power demand is considerably less (half or less) than that during ‘Climb Out’ phase but significantly larger (~ three times) than that required during ‘Taxi- out’ phase.
Taxi-in / Idle-in: The operational phase after landing until the aircraft is parked and the engines are shut down. The power demand is the same as the ‘Taxi-out’ phase.

The typical activity at each airport is the LTO counts for each aircraft type. The historical and current annual use-type sorted LTO count data for the three large commercial airports in the SFBA for years 1990-2023 is available through the Federal Aviation Administration’s Terminal Area Forecast (TAF) data archives (FAA, 2024).

It should be noted that CARB has already developed airport specific mixing heights (instead of using the default of 3000 ft AGL for all airports) which will be incorporated in future inventory updates.

Commercial Passenger and Cargo Operations

The passenger airliner and freighter cargo operations take place at three large commercial SFBA airports (OAK, SFO, and SJC). The annual activity counts (years 1990-2023) are derived from the TAF database. Airport-specific forecast reports (OAK, 2022; SFO, 2016; SJC, 2017) are used to derive the proportional splits between the passenger airliner and cargo freighter use-type classifications; in order to further split the ‘air carrier’ activity in the TAF database.

Complete annual LTO count, and fleet distribution (by aircraft manufacturers and model numbers) data were also received from three major SFBA commercial airports in recent years (personal communication with Colleen Liang at OAK airport, Elsa Jacobo at SJC airport, and SFO 2023). Fleet distribution from the year 2019 is used in further aircraft-specific use-type classifications and emissions calculations for OAK and SJC airport source categories, as the years following were considered either non-representative (due to the impacts of COVID pandemic) or were not available at the time of inventory estimation. The fleet distribution for SFO airport is from year 2023 (SFO, 2023).

Commuter Air Taxi Operations

The CAT annual activity counts (years 1990-2023) are derived from the TAF database for the three large commercial airports and the nine small FAA ATC towered airports.

General Aviation Aircraft Operations

The GA annual activity counts (years 1990-2023) are derived from the TAF database for the three large commercial airports and the eight small FAA ATC towered airports. The GA total activity is further split into GA-piston engine and GA-jet engine source categories (for all airports) using the fleet distribution data obtained from HWD airport (HWD, 2024) and assuming that to be a representative distribution for all SFBA GA airports.

For the twelve remaining non-towered airports, GA activity has been retrieved through direct communication with the airports over the past decade. The activity at these non-towered GA airports is substantially lower in comparison to that at other SFBA airports.

Military Aircraft Operations

The military airport activity data for Travis Air Force Base (AFB) in Solano County is derived from a comprehensive report provided to Air District staff in year 2010 that details the annual activity counts and military fleet distribution for year 2009 (TAFB, 2009). Since no new report or recent LTO data is available for Travis AFB, the overall activity data from the year 2009 (27,051 LTO) is held constant with certain assumptions:

Fleet distribution is not held constant.
Starting in the year 2020, the KC10 airplane LTO count goes down uniformly, until it reaches zero by year 2024 (KC135, 2024).
The LTO count of KC135 reduces uniformly from the year 2020 and goes down to zero by year 2032 (KC135, 2024).
The LTO count of KC46A aircraft increases uniformly to account for the decreasing activity of KC10 and KC135 while the overall Travis AFB count does not change (KC135, 2024).

For Moffett Field (NUQ), Planetary Ventures (PV) – a Google Inc. subsidiary, entered into a 60-year lease term with National Aeronautics and Space Administration (NASA) in 2015, to operate NUQ as a joint civil-military airport. The aircraft operations activity counts at NUQ from year 2015 onwards, along with proportional splits across major use-types, is directly obtained from PV (NUQ, 2024).

Three source categories account for only historical emissions from now closed airports – Alameda Naval Air Station (category 639 – jet engines, and category 682 – piston engines) and Travis Aero Club (category 593 – piston engines). An example of complete activity count for the base year 2023 for Oakland International Airport is shown below:

Category Number	Category Description	Annual Activity (LTOs)
1119	Passenger Aircraft	97,185
1128	Cargo Aircraft	17,150
1131	Commuter Air Taxi	24,286
443	General Aviation, Jet	11,293
475	General, Aviation, Piston	56,494
673	Military, Jet	686
702	Military, Piston	7

Agricultural Aircraft Operations

The annual activity for source category 711 is acreage of agricultural land in the SFBA that is sprayed with pesticides. This information is derived from the annual Pesticide Use Reports (PUR) issued by the California Department of Pesticide Regulation (CADPR, 2021). Acreage data for SFBA counties is available through the year 2021, so an average of five years (2017-2021) is used to estimate the sprayed agricultural acreage for base year 2022.

County Distribution / Fractions

Exact annual activity counts for each aircraft operating at each SFBA airport are available and collected, and/or estimated. As a result, almost all source categories included in the Aviation subsector are scoped to be specific to each airport. As a result, county fractions are not required and included in the emissions calculation approach. Airport-specific emissions are aggregated at the end of the calculations process to derive the county-specific emissions totals. County-specific agricultural acreage sprayed data is available to determine the county-fractions for the Agricultural Aircraft source category (711).

ID	Description	ALA	CC	MAR	NAP	SM	SNC	SOL	SON
1115	Commercial Aircraft - Major Passenger Aircraft - San Francisco International Airport	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
1119	Commercial Aircraft - Major Passenger Aircraft - Oakland International Airport	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
1123	Commercial Aircraft - Major Passenger Aircraft - San Jose International Airport	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
1127	Commercial Aircraft - Cargo Aircraft - San Francisco International Airport	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
1128	Commercial Aircraft - Cargo Aircraft - Oakland International Airport	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
1129	Commercial Aircraft - Cargo Aircraft - San Jose International Airport	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
1130	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Francisco International Airport	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
1131	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Oakland International Airport	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
1132	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Jose International Airport	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
1689	General Aviation - Piston Aircraft - Byron	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
2733	General Aviation - Jet Aircraft - Palo Alto	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2734	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Napa County	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
2735	Military Aircraft - Jet Aircraft - Napa County	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
2736	Military Aircraft - Piston Aircraft - Napa County	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
2737	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Buchanan Field	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
2738	Military Aircraft - Jet Aircraft - Buchanan Field	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
2739	Military Aircraft - Piston Aircraft - Buchanan Field	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
2740	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Hayward	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2741	Military Aircraft - Jet Aircraft - Hayward	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2742	Military Aircraft - Piston Aircraft - Hayward	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2743	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Livermore	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2744	Military Aircraft - Jet Aircraft - Livermore	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2745	Military Aircraft - Piston Aircraft - Livermore	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
2746	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Palo Alto	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2747	Military Aircraft - Jet Aircraft - Palo Alto	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2748	Military Aircraft - Piston Aircraft - Palo Alto	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2749	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Reid-Hillview	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
2750	Military Aircraft - Jet Aircraft - Reid-Hillview	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
2751	Military Aircraft - Piston Aircraft - Reid-Hillview	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
2752	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Carlos	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2753	Military Aircraft - Jet Aircraft - San Carlos	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2754	Military Aircraft - Piston Aircraft - San Carlos	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
2755	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Sonoma County	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
2756	Military Aircraft - Jet Aircraft - Sonoma County	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
2757	Military Aircraft - Piston Aircraft - Sonoma County	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
2759	General Aviation - Jet Aircraft - Moffett Field	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
2760	General Aviation - Piston Aircraft - Moffett Field	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
441	General Aviation - Jet Aircraft - Livermore	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
442	General Aviation - Jet Aircraft - Hayward	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
443	General Aviation - Jet Aircraft - Oakland North	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
444	General Aviation - Jet Aircraft - Buchanan Field	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
446	General Aviation - Jet Aircraft - Gnoss Field	0.0	0.00	1.0	0.00	0.0	0.00	0.00	0.00
447	General Aviation - Jet Aircraft - Napa County	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
448	General Aviation - Jet Aircraft - Half Moon Bay	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
449	General Aviation - Jet Aircraft - San Carlos	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
450	General Aviation - Jet Aircraft - San Francisco International	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
451	General Aviation - Jet Aircraft - Reid-Hillview	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
452	General Aviation - Jet Aircraft - San Jose International	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
453	General Aviation - Jet Aircraft - South County	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
455	General Aviation - Jet Aircraft - Sonoma County	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
456	General Aviation - Piston Aircraft - Livermore	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
463	General Aviation - Piston Aircraft - Hayward	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
475	General Aviation - Piston Aircraft - Oakland North	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
489	General Aviation - Piston Aircraft - Buchanan Field	0.0	1.00	0.0	0.00	0.0	0.00	0.00	0.00
496	General Aviation - Piston Aircraft - Gnoss Field	0.0	0.00	1.0	0.00	0.0	0.00	0.00	0.00
503	General Aviation - Piston Aircraft - Marin /Smith Ranch (Pvt)	0.0	0.00	1.0	0.00	0.0	0.00	0.00	0.00
505	General Aviation - Piston Aircraft - Parrett/Angwin	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
511	General Aviation - Piston Aircraft - Napa County	0.0	0.00	0.0	1.00	0.0	0.00	0.00	0.00
520	General Aviation - Piston Aircraft - Half Moon Bay	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
527	General Aviation - Piston Aircraft - San Carlos	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
534	General Aviation - Piston Aircraft - San Francisco International	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
541	General Aviation - Piston Aircraft - Palo Alto	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
548	General Aviation - Piston Aircraft - Reid-Hillview	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
555	General Aviation - Piston Aircraft - San Jose International	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
562	General Aviation - Piston Aircraft - South County	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
597	General Aviation - Piston Aircraft - Sonoma County	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
615	General Aviation - Piston Aircraft - Petaluma Sky Ranch	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
626	General Aviation - Piston Aircraft - Sonoma Valley/Schelville	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
632	General Aviation - Piston Aircraft - Sonoma SkyPark	0.0	0.00	0.0	0.00	0.0	0.00	0.00	1.00
646	Military Aircraft - Jet Aircraft - Moffett Field	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
658	Military Aircraft - Jet Aircraft - Travis AFB	0.0	0.00	0.0	0.00	0.0	0.00	1.00	0.00
670	Military Aircraft - Jet Aircraft - San Francisco International	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
673	Military Aircraft - Jet Aircraft - Oakland International	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
676	Military Aircraft - Jet Aircraft - San Jose International	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
687	Military Aircraft - Piston Aircraft - Moffett Field	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
694	Military Aircraft - Piston Aircraft - Travis AFB	0.0	0.00	0.0	0.00	0.0	0.00	1.00	0.00
699	Military Aircraft - Piston Aircraft - San Francisco International	0.0	0.00	0.0	0.00	1.0	0.00	0.00	0.00
702	Military Aircraft - Piston Aircraft - Oakland International	1.0	0.00	0.0	0.00	0.0	0.00	0.00	0.00
705	Military Aircraft - Piston Aircraft - San Jose International	0.0	0.00	0.0	0.00	0.0	1.00	0.00	0.00
711	Agricultural Aircraft - Piston Aircraft	0.0	0.28	0.0	0.05	0.0	0.05	0.58	0.03

BAAQMD Jurisdiction Fraction

The BAAQMD jurisdiction in the San Francisco Bay Area (SFBA) accounts for only a portion of Solano and Sonoma counties. The remaining area in these counties is covered by other Air Districts.

All 84 aviation source categories represent operations occurring at an airport that is geographically located within the Air District’s legal boundaries. For Agricultural Aircraft source category (711), the land-area split for Solano (48%) and Sonoma (37.4%) is used to apportion the agricultural acreage sprayed that is attributed to the Air District.

Emission Factors

Emission factors (EFs) for the aviation fuel combustion subsector are based on a LTO cycle that accounts for those GHG emissions that occur below the mixing height. The EFs are calculated based on a formula and data laid out in Section 2.6.1.1 (USDAF, 2024a), as follows:

Emission Factor_pollutant = ∑[(TIM_i/60) ×(FFR_i/1000) ×EF_i×(FERF/100)] × N

Where:

Emission Factor_pollutant = Pollutant emission factor for each aircraft classification being evaluated (lb / LTO)

N = Number of engines per aircraft being evaluated

i = Mode identifier, 1 = Taxi-out, 2 = Takeoff, 3 = Climb out, 4 = Approach, and 5 = Taxi-in

TIM_i = Time spent in each mode per LTO cycle (minute / LTO)

FFR_i = Fuel flow rate during operational mode per aircraft engine (lb of fuel / hour)

EF_i = Pollutant emission factor for specified mode (lb of pollutant emitted / 1000 lb fuel burned)

FERF = Fuel emission reduction factor, if applicable (%), in cases where alternative fuel is used

The mass-based EF_ifor all aircraft operations is based on the combustion of JP-8 fuel with a density of 6.71 lb/gallon. The EF_ifor a GHG pollutant is the same for any operational mode i (assuming full combustion) and is as follows:

A master list of over 60 aircraft engine types is prepared based on a comprehensive list of aircraft manufacturer/model-based annual LTO counts received from three major SFBA commercial airports for recent years (personal communication with Colleen Liang at OAK airport, Elsa Jacobo at SJC airport, and SFO 2023). For each of these aircraft engine models, the fuel flow rate for each operational mode (FFR_i) is assigned based on a detailed repository in Table 2.8 (USDAF, 2024a), and default time-in-mode (TIM_i) for various aircraft categories is based on the classification available in Table 2.4 (USDAF, 2024a). The fuel emissions reduction factor is 1.0 for JP-8 fuel but will be <1.0 for blends with alternative or sustainable aviation fuel (SAF). In this way, a master pollutant-specific emission-factor list, based on emissions produced per a single LTO cycle, is generated for each aircraft operating in the SFBA. This includes emission factors for all models of passenger, cargo and commuter air taxi aircraft operating out of SFBA’s three large commercial airports, as well as all major General Aviation aircraft operating at OAK airport (which has a considerable GA annual activity count). An example of this emission factor derivation is shown for a single aircraft example in the Sample Calculations subsection.

This master-list of aircraft-specific emission factors is then used to derive activity-weighted fleet-averaged emission factors for each source category. Below is a summary of these fleet-averaged use-type based emission factors for source categories at the three commercial SFBA airports.

Category Number	Source Classification	Airport	EF (lbs of pollutant in CO₂ equivalent / LTO)
Category Number	Source Classification	Airport	CO₂	CH₄	N₂O
1119	Passenger Airliner	OAK	7476	12	19
1128	Cargo Airplane	OAK	7476	12	19
1131	Commuter Air Taxi	OAK	1089	2	3
1115	Passenger Airliner	SFO	8107	13	20
1127	Cargo Airplane	SFO	18087	28	45
1130	Commuter Air Taxi	SFO	1160	2	3
1123	Passenger Airliner	SJC	5948	9	15
1129	Cargo Airplane	SJC	5948	9	15
1132	Commuter Air Taxi	SJC	1387	2	3.4
443, 450, 452	General Aviation - Jet	OAK, SFO, SJC	887	1.4	2.2
475, 534, 555	General Aviation - Piston	OAK, SFO, SJC	45	0.07	0.11

Commercial Passenger and Cargo Operations

As shown in the table above, the fleet-averaged EFs for passenger airliners and cargo freighters for each of the three large airports (covering six source categories) are derived using the master-list of aircraft-specific emission factors, and fleet count and distribution data received from the individual airports for a representative recent year (year 2023 for OAK, SFO and SJC airports).

Commuter Air Taxi Operations

The CAT fleet-averaged EF is generated for the three commercial airports in the SFBA using the master-list of aircraft-specific emission factors, and fleet count and distribution data received from the individual airports for a representative recent year (year 2023 for OAK, SFO and SJC airports).

The fleet-averaged CAT EF generated for OAK airport is also used for all FAA ATC towered airports (9 source categories).

General Aviation Aircraft Operations

The aircraft-specific GA fleet activity and distribution data is only available for OAK airport (for years 2019 and 2023) as GA activity at SFO and SJC is too sparse in present years. Due to the lack of aircraft-specific GA fleet activity data for all other GA airports, the GA-jet and GA-piston fleet-averaged EFs estimated for OAK airport are used to estimate emissions for all GA source categories across SFBA airports, including the ones for large commercial airports (6 source categories), small FAA ATC towered airports (16 source categories), NUQ civil-military airport (2 source categories), and non-towered airports (12 source categories).

Military Aircraft Operations

For military operation emission factors, aircraft- and site-specific emission factors are derived by U.S. Department of Air Force for each air force base (AFB) in the nation. The aircraft- and site-specific emission factors for Travis AFB are provided to Air District staff on request (USDAF, 2024b). The aircraft/site-specific mass per LTO EFs provided by DAF are only conditionally releasable and come with a disclaimer that these EFs are a snapshot in time, and although the best available data at the time, they are subject to change. The individual aircraft/site-specific EFs for Travis AFB are not shown here due to confidentiality agreement with USDAF.

The Air District staff utilize the aircraft/site-specific EFs for Travis AFB (in Solano County) and combines them with fleet activity and fleet distribution data for each year (TAFB, 2009; KC135, 2024) to generate fleet-averaged Travis AFB EFs. The fleet-averaged EF for Travis AFB for year 2023 is shown here:

Category Number	Source Classification	Airport	EF (lbs of pollutant in CO₂ equivalent / LTO)
Category Number	Source Classification	Airport	CO₂	CH₄	N₂O
658	Military - Jet	Travis AFB	15302	22	37
694	Military - Piston	Travis AFB	15618	22	37

The fleet-average Travis AFB EFs listed above are also used for estimating emissions for all military aircraft activity at eight small FAA ATC-towered airports, NUQ civil-military airport, and three large commercial airports (total of 24 active source categories).

Agricultural Aircraft Operations

The emission factor for source category 711 is generated from a fleet average fuel consumption rate that is derived from EPA-sourced data for seven agricultural aircraft (CARB, 1990) and updated in the year 2001 by BAAQMD (BAAQMD, 2001). This average fuel-consumption rate of 0.1053 gallon per acre sprayed is then combined with the mass-based pollutant-specific E_i listed above to derive GHG emissions factors on a per acre sprayed basis.

Control Factors / Emission Controls

Presently there are no state-wide or Air District implement regulations that reduce the estimated GHG emissions from any use-type within the aviation industry. Hence historical and current GHG emissions for all aviation source categories are unaffected.

Historical Emissions / Backcast

For all aviation source categories across the three main commercial and nine FAA ATC towered airports (a total of 66 source categories), annual LTO counts are available from FAA (FAA, 2024), starting from year 1990 for each of the use-type classifications including Passenger, Cargo, CAT, GA and Military. Hence historical emissions can be estimated directly from the derived fleet-averaged EFs back to the year 1990 without the need to back cast emissions using a growth profile. For the five source categories attributed to Moffett Field, historical emissions for the years 1990-2014 are based on the average activity of the year 2015-2023 and are held constant during that time period. For the twelve small non-towered airports, historical airport activity is scaled from the year 2011 activity value and projected back to the year 1990, using a FAA-issued national level aviation fuel sale growth profile. Thus, historical emissions at these small airports scale to aviation fuel sale. For the two source categories at Travis AFB, total activity data (and fleet distribution) is assumed to be constant throughout the entire duration between years 1990-2019, and hence annual emissions remain constant. There are also three inactive source categories for previously active airports/air bases (Travis Aero Club, Alameda NAS) in SFBA that have historical emissions for earlier years. For Agricultural Aircrafts source category (711), activity data in the form of agricultural land acreage sprayed with pesticides is available, dating back to year 1990 (CADPR, 2021), and historical emissions are derived from this activity data.

Future Projections / Growth Factor

For all aviation source categories across the three main commercial airports (a total of 21 source categories), airport-specific terminal area forecasting (TAF) growth profiles for annual LTO counts are available from FAA (FAA, 2024). These growth profiles are applied to all Passenger, Cargo and CAT source categories. The TAF growth profile for SFO is adjusted due to constraints on projected capacity (SFO, 2024a), that results in the projected LTO counts being capped after the year 2030. TAF growth profiles are also available for forecasting activity growth under the General Aviation classification at three large commercial airports and nine small FAA ATC towered airports. These profiles are consolidated to generate a single Bay Area-specific GA growth profile which is then used to forecast emissions for all twelve non-towered airports in the SFBA.

For Travis AFB, as mentioned before in the Activity subsection, the overall activity count is kept constant to the year 2050. The emissions for categories 658 and 694 vary from year 2020 to year 2032, during the phase-in of KC46A airplanes and phase-out of KC10 and KC135 airplanes (KC135, 2024). The total emissions remain constant after the year 2032 as the fleet distribution and overall activity remains constant.

Fuel consumption by agricultural aircraft for pesticide spraying activities is forecasted from year 2023-2050, in the latest edition of CARB’s OFFROAD inventory model (CARB, 2024a). Forecasted emissions for source category # 711 are derived using this forecast profile. It is expected that CARB’s annual estimates of this source category in their Off-Road inventory model will replace the current methodology to estimate Agricultural Aircrafts in the near future.

Recently, SFO airport has been leading the charge among U.S. airports in Sustainable Aviation Fuel (SAF) adoption (SFO, 2024b). The SFO administration claims that flights out of SFO refuel with among the highest SAF volumes globally due to California’s industry-leading Low Carbon Fuel Standard (LCFS) and SFO's dedicated advocacy, which collectively aims to bring SAF prices closer to price parity with traditional jet fuel. AB1322 state law requires the state to align with the Governor’s 20% Clean Fuels target for the aviation sector by year 2030. SFO continues to convene a SAF Coalition to advocate for additional incentives at the state and federal level to decarbonize the industry and help SFO hit its goal of 5% SAF by 2025. If implemented, this would lead to a fuel emission reduction factor (FERF) of 0.95 in the EF calculations for all SFO source categories. This would lead to an overall 5% decline in projected GHG emissions at SFO airport. Since this goal is voluntary and unverified, the current forecasted emissions curve only reflects a business-as-usual scenario and does not account for any potential reductions owing to increased use of SAF.

In October 2024, the CARB signed a memorandum of understanding (non-binding MOU) with Airlines for America (A4A), an industry trade organization representing nearly a dozen major airlines (CARB, 2024b). This agreement aims to dramatically accelerate the use of SAF for intrastate flights. The agreement projects to use 200 MGPY of SAF in California by 2035, an amount that would meet about 40% of intrastate travel demand – a more than tenfold increase from current levels. The impact of this MOU if implemented would lead to increased SAF use across all three major airports in the SFBA and a subsequent reduction in GHG emissions owing to use of a FERF < 1.0 in emissions calculations.

Sample Calculations

The table below shows an example calculation for estimating base year 2023 CO₂ emissions for all cargo airplane traffic (source category 1127) at SFO airport in San Mateo County.

Step 1	Year 2023 SFO Air Carrier operations (FAA, 2024)	346,766
Step 2a	Cargo Aircraft proportion from airport forecasting report and fleet distribution data (SFO, 2016; SFO, 2023)	1.46%
Step 2b	Year 2023 SFO Cargo Aircraft operations	= 346,766 × 0.0146 = 5062
Step 3a	Gather engine time-in-mode (TIM) per LTO of example cargo freighter (USDAF, 2024a) - Boeing 772 (B777 family), with two PW4098 engines (Pratt Whitney)	Taxi-out = 19 mins Takeoff = 0.7 mins Climb out = 2.2 mins Approach = 4 mins Taxi-in =7 mins
Step 3b	Gather engine fuel flow rate (FFR) of example cargo freighter (USDAF, 2024a) - Boeing 772 (B777 family), with two PW4098 engines (Pratt Whitney)	Taxi-out = 2548 lbs/hour Takeoff = 32841 lbs/hour Climb out = 25754 lbs/hour Approach = 8532 lbs/hour Taxi-in = 2548 lbs/hour
Step 3c	Derive CO₂ emission factor of JP-8 fuel with density of 6.71 lbs-fuel/gal and emission rate of 9.75 kg-CO₂/gal	= (9.75 kg/gal × 2.205 lbs-CO₂/kg) ÷ (6.71 lbs-fuel/gallon × 1000) = 3203 lbs-CO₂/1000 lb-fuel
Step 3d	Derive LTO-based fuel consumption rate for B772 cargo freighter	= [((19 min + 7 min) × 2548 lb/hr) + (0.7 min × 32841 lb/hr) + (2.2 min × 25754 lb/hr) + (4 min × 8532 lb/hr)] × 2 engines ÷ 60 min/hour = 6001 lbs-fuel per LTO
Step 3e	Derive LTO-based activity-weighted fuel consumption rate of all seven cargo aircraft landing at SFO in year 2023	= 5647 lbs-fuel per LTO
Step 4	Derive LTO-based CO₂ Emission Factor for B772 cargo freighter	= [3203 lb-CO₂/1000 lb-fuel × 5647 lbs-fuel per LTO] = 18,087 lbs-CO₂/LTO
Step 5	Derive year 2023 CO₂ emissions for SFO Air Carrier operations	= [5062 operations ÷ (2 operations/LTO)] × (18,087 lbs-CO₂/LTO)] = 45,778,956 lbs-CO₂
Step 6	Calculate emissions in metric tons of CO₂-equivalent (MTCO₂eq)	= 45,778,956 lbs-CO₂ ÷ 2204.62 lb/MT = 20,765 MTCO₂eq

Assessment of Methodology

All Aviation subsector source categories have undergone a major update in emissions calculation methodology and sourcing of activity and emission factor data since the previous GHG inventory update which was published in year 2017 (BAAQMD, 2015).

Base Year	Revision	Reference
2023	Updated activity data for three commercial airports data and eight General Aviation airports from FAA’s TAF database, and for Moffett Airfield through direct communication with operator Derived aircraft-specific LTO-based EFs for over 60 aircraft using detailed and recent engine models, time-in-mode and fuel flow rate information (including for general aviation jet and piston engine aircraft) Updated fleet distribution at three commercial airports based on custom airport-specific information Updated fleet distribution for eight FF ATC-towered airports and for NUQ airport based on Hayward GA airport’s 2023 fleet mix Updated Travis AFB emissions using site- and aircraft-specific emissions per LTO database generated by USDAF Updated Travis AFB fleet-mix for historical, current and future years Updated Agricultural Aircraft activity data using annual Pesticide Use Reports Updated military aircraft EFs at all commercial and ATC-towered airports using Travis AFB’s fleet-average EF Updated General Aviation emission factors for eight towered, twelve non-towered, and NUQ GA airports in the SFBA using OAK’s fleet-average GA EF Updated emissions forecasting techniques and/or growth profiles for most source categories Deactivated and retired small airport source categories that closed down before year 1990	FAA, 2024; NUQ, 2024 USDAF, 2024a OAK, 2022; SFO, 2016; SFO, 2023; SJC, 2017; personal communication with staff at OAK and SJC airports HWD, 2024 USDAF, 2024b KC135, 2024; TAFB, 2009 CADPR, 2021 USDAF, 2024b Personal communication, OAK airport CARB, 2024a; FAA 2024; SFO, 2024a Freeman, 2024
2015	Activity data was updated using intermittent data requests to airports Forecasting of all major airport emissions was done based on aviation fuel sale profiles, and not based on airport-specific forecasts Emission factors derived for major airports were based on limited fleet distribution information GA fleet distribution between jet and piston engine aircraft was held constant for all towered and non-towered airports for all years GA emission factor was based on data from 2000s	BAAQMD, 2015 BAAQMD, 2015 BAAQMD, 2015 BAAQMD, 2015 BAAQMD, 2015

Emissions

The table below shows the total GHG emissions by pollutant in metric tons of CO₂ equivalent (MTCO₂eq) for the Aviation subsector.

ID	Description	CH4	CO2	N2O	Total
1115	Commercial Aircraft - Major Passenger Aircraft - San Francisco International Airport	858.4	547012.4	1354.2	549225.0
658	Military Aircraft - Jet Aircraft - Travis AFB	276.3	193238.0	472.5	193986.8
1119	Commercial Aircraft - Major Passenger Aircraft - Oakland International Airport	263.5	167936.7	415.8	168616.0
1123	Commercial Aircraft - Major Passenger Aircraft - San Jose International Airport	228.3	145475.2	360.2	146063.7
1128	Commercial Aircraft - Cargo Aircraft - Oakland International Airport	46.5	29635.9	73.4	29755.8
1127	Commercial Aircraft - Cargo Aircraft - San Francisco International Airport	28.4	18075.8	44.8	18149.0
646	Military Aircraft - Jet Aircraft - Moffett Field	24.3	17022.9	41.6	17088.8
670	Military Aircraft - Jet Aircraft - San Francisco International	16.7	11663.4	28.5	11708.6
1130	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Francisco International Airport	17.0	10837.0	26.8	10880.8
1132	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Jose International Airport	11.0	7034.2	17.4	7062.6
1131	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Oakland International Airport	10.9	6945.4	17.2	6973.5
441	General Aviation - Jet Aircraft - Livermore	9.0	5736.0	14.2	5759.2
2733	General Aviation - Jet Aircraft - Palo Alto	7.6	4829.7	12.0	4849.3
451	General Aviation - Jet Aircraft - Reid-Hillview	7.3	4665.5	11.6	4684.4
2735	Military Aircraft - Jet Aircraft - Napa County	6.1	4263.7	10.4	4280.2
676	Military Aircraft - Jet Aircraft - San Jose International	6.1	4251.7	10.4	4268.2
442	General Aviation - Jet Aircraft - Hayward	6.2	3923.8	9.7	3939.7
673	Military Aircraft - Jet Aircraft - Oakland International	4.9	3446.8	8.4	3460.1
444	General Aviation - Jet Aircraft - Buchanan Field	4.8	3080.5	7.6	3092.9
2752	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - San Carlos	4.7	2977.1	7.4	2989.2
2734	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Napa County	4.4	2831.6	7.0	2843.0
1129	Commercial Aircraft - Cargo Aircraft - San Jose International Airport	4.1	2620.3	6.5	2630.9
2755	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Sonoma County	3.8	2413.4	6.0	2423.2
449	General Aviation - Jet Aircraft - San Carlos	3.6	2304.4	5.7	2313.7
443	General Aviation - Jet Aircraft - Oakland North	3.6	2282.3	5.7	2291.6
455	General Aviation - Jet Aircraft - Sonoma County	3.4	2149.4	5.3	2158.1
694	Military Aircraft - Piston Aircraft - Travis AFB	2.9	1997.7	4.9	2005.5
456	General Aviation - Piston Aircraft - Livermore	2.8	1776.3	4.4	1783.5
447	General Aviation - Jet Aircraft - Napa County	2.5	1586.4	3.9	1592.8
541	General Aviation - Piston Aircraft - Palo Alto	2.3	1495.7	3.7	1501.7
2756	Military Aircraft - Jet Aircraft - Sonoma County	2.1	1494.3	3.7	1500.1
2737	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Buchanan Field	2.3	1447.3	3.6	1453.2
548	General Aviation - Piston Aircraft - Reid-Hillview	2.3	1444.8	3.6	1450.7
463	General Aviation - Piston Aircraft - Hayward	1.9	1215.1	3.0	1220.0
2741	Military Aircraft - Jet Aircraft - Hayward	1.6	1103.8	2.7	1108.1
452	General Aviation - Jet Aircraft - San Jose International	1.7	1103.0	2.7	1107.4
496	General Aviation - Piston Aircraft - Gnoss Field	1.6	994.6	2.5	998.7
489	General Aviation - Piston Aircraft - Buchanan Field	1.5	954.0	2.4	957.9
2743	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Livermore	1.4	862.4	2.1	865.9
2738	Military Aircraft - Jet Aircraft - Buchanan Field	1.2	860.7	2.1	864.0
2744	Military Aircraft - Jet Aircraft - Livermore	1.2	852.7	2.1	856.0
1689	General Aviation - Piston Aircraft - Byron	1.2	739.1	1.9	742.2
446	General Aviation - Jet Aircraft - Gnoss Field	1.1	715.6	1.8	718.5
527	General Aviation - Piston Aircraft - San Carlos	1.1	713.6	1.8	716.5
597	General Aviation - Piston Aircraft - Sonoma County	1.0	665.6	1.7	668.3
475	General Aviation - Piston Aircraft - Oakland North	0.9	574.7	1.4	577.0
615	General Aviation - Piston Aircraft - Petaluma Sky Ranch	0.9	562.6	1.4	564.9
520	General Aviation - Piston Aircraft - Half Moon Bay	0.8	522.7	1.3	524.8
511	General Aviation - Piston Aircraft - Napa County	0.8	491.3	1.2	493.3
2753	Military Aircraft - Jet Aircraft - San Carlos	0.7	458.2	1.1	460.0
2740	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Hayward	0.7	449.4	1.1	451.2
562	General Aviation - Piston Aircraft - South County	0.5	347.2	0.9	348.6
450	General Aviation - Jet Aircraft - San Francisco International	0.5	303.2	0.8	304.5
555	General Aviation - Piston Aircraft - San Jose International	0.4	277.7	0.7	278.8
2759	General Aviation - Jet Aircraft - Moffett Field	0.3	221.7	0.5	222.5
2749	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Reid-Hillview	0.3	203.1	0.5	203.9
503	General Aviation - Piston Aircraft - Marin /Smith Ranch (Pvt)	0.3	198.2	0.5	199.0
2747	Military Aircraft - Jet Aircraft - Palo Alto	0.3	187.3	0.5	188.1
626	General Aviation - Piston Aircraft - Sonoma Valley/Schelville	0.3	169.6	0.4	170.3
632	General Aviation - Piston Aircraft - Sonoma SkyPark	0.2	158.0	0.4	158.6
687	Military Aircraft - Piston Aircraft - Moffett Field	0.2	157.7	0.4	158.3
2746	Commercial Aircraft - Commuter/Taxi (Air Taxi) Aircraft - Palo Alto	0.2	157.3	0.4	157.9
711	Agricultural Aircraft - Piston Aircraft	0.2	155.5	0.3	156.0
2750	Military Aircraft - Jet Aircraft - Reid-Hillview	0.2	119.5	0.3	120.0
699	Military Aircraft - Piston Aircraft - San Francisco International	0.2	108.1	0.3	108.6
505	General Aviation - Piston Aircraft - Parrett/Angwin	0.2	104.0	0.3	104.5
448	General Aviation - Jet Aircraft - Half Moon Bay	0.2	98.8	0.2	99.2
534	General Aviation - Piston Aircraft - San Francisco International	0.1	76.3	0.2	76.6
2760	General Aviation - Piston Aircraft - Moffett Field	0.1	68.6	0.2	68.9
453	General Aviation - Jet Aircraft - South County	0.1	65.7	0.2	66.0
2736	Military Aircraft - Piston Aircraft - Napa County	0.1	39.5	0.1	39.7
705	Military Aircraft - Piston Aircraft - San Jose International	0.1	39.4	0.1	39.6
702	Military Aircraft - Piston Aircraft - Oakland International	0.0	31.9	0.1	32.0
2757	Military Aircraft - Piston Aircraft - Sonoma County	0.0	13.8	0.0	13.8
2742	Military Aircraft - Piston Aircraft - Hayward	0.0	10.2	0.0	10.2
2739	Military Aircraft - Piston Aircraft - Buchanan Field	0.0	8.0	0.0	8.0
2745	Military Aircraft - Piston Aircraft - Livermore	0.0	7.9	0.0	7.9
2754	Military Aircraft - Piston Aircraft - San Carlos	0.0	4.2	0.0	4.2
2748	Military Aircraft - Piston Aircraft - Palo Alto	0.0	1.7	0.0	1.7
2751	Military Aircraft - Piston Aircraft - Reid-Hillview	0.0	1.1	0.0	1.1

Summary of Base Year 2023 Emissions

Aviation is an important source of GHG emissions in the region. The subsector constitutes ~2% of SFBA’s regional GHG emissions and ~5.5% of the Transportation sector GHG emissions. Emissions from passenger airliner traffic at the three large commercial airports in SFBA (categories 1115,1119 and 1123) constitute over 70% of the subsector’s total emissions. Military-designated emissions at Travis AFB, based on 2009 total activity data but an evolving fleet-mix (KC135, 2024), constitute the second largest airport emissions (~17%) in the SFBA, after the all use-type combined emissions at San Francisco Airport (> 48%). General Aviation at ATC-towered and non-towered small airports across SFBA account for less than 5% of the regional aviation GHG emissions.

The tables below show the contribution of Aviation subsector GHG emissions relative to the Transportation sector and to the regional SFBA totals.

Contribution of Aviation Emissions by Sector

Subsector	Sector	Subsector GHG Emissions (MMTCO2eq)	Sector GHG Emissions (MMTCO2eq)	% of Sector
Aviation	Transportation	1.24	22.60	5.49%

Contribution of Aviation Emissions to Regional Total

Subsector	Subsector GHG Emissions (MMTCO2eq)	Regional Total GHG Emissions (MMTCO2eq)	% of Regional Total
Aviation	1.24	65.68	1.89%

Trends

The time series chart below shows the emission trends for various source categories in the Aviation subsector.

Summary of Trends

The variability in the historical aviation emissions trends is mostly driven by the passenger airline activity at the three large commercial airports. This is because the total military aircraft operations count at Travis AFB (only available for the year 2009) is held constant from the year 1990 through 2050, although the fleet mix at Travis AFB is evolving.

In the commercial passenger airline segment, the fleet distribution has evolved towards Airbus and Boeing airplanes that are more fuel efficient. This overall development led to a general decrease in regional aviation GHG emissions in the 1990s and 2000s. But following the recovery from the 2009 economic recession, passenger air travel rate has been increasing at a steady rate, and this led to a rise in regional aviation emissions during the 2010s all the way to their peak, until the COVID pandemic in 2020. The pandemic led to a near-complete halt in passenger air travel for many months, and the subsequent years saw a decline in air travel. This factor led to a sharp 30-40% decline in regional aviation GHG emissions in 2020-2022. Going forward, FAA activity forecasts suggest a return to pre-pandemic operations levels at OAK, SFO and SJC by years 2025-26. Following that, aviation GHG emissions, largely driven by increase in passenger air travel activity, will continue to rise at OAK and SJC airports as the forecasted capacity at these airports continue to rise. At SFO, forecasted aircraft operations continue to rise until the year 2030, when the airport reached its maximum capacity, and traffic (and thereby emissions) are predicted to remain steady after that.

Uncertainties

The main uncertainty in the updated methodology arises from the assumption of a constant count of operations at Travis AFB for all inventory years (1990-2050). Another uncertainty is the lack of accounting of helicopter emissions occurring at any SFBA airport, although that activity is still insignificant compared to the commercial passenger activity at the three large SFBA airports. The CARB inventory model (CAI, 2024) is expected to address the lack of helicopter emission in the Air District inventory. The USDAF methodology to estimate LTO-cycle emission factors is rooted in the assumption of a default height for mixing layer (3000 feet AGL), which results in fixed values of time-in-mode for each operation for each aircraft engine. It has been demonstrated conclusively that this assumption can lead to a significant bias as the range of mixing layer depths, as well as the annual mean mixing layer depth at each of the three SFBA large commercial airports can be quite different from 3000 feet AGL. The CAI 2024 inventory is expected to use time-varying mixing layer heights for all major airports for emissions calculations which will improve the representativeness of the derived emission factors. Although the overall magnitude of GA subgroup emissions is minor as compared to the contribution of Commercial and Military aircraft subgroups to the Aviation subsector GHG emissions inventory, the use of a fleet-averaged EF derived from GA activity at OAK airport as a substitute for the fleet-distribution at all GA airports adds additional uncertainty to the overall inventory.

Contact

Author: Abhinav Guha

Reviewer: Virginia Lau

Last Update: 07/21/2025

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