6.13 Aircraft Fueling

Categories 79, 80, and 1906

6.13.1 Introduction

Categories 79, 80, and 1906 account for organic emissions (TOG and ROG) that occur during the refueling (including spillage) of general aviation, commercial, and military aircraft with aviation gasoline or jet fuel.

There are two systems used by airports for the refueling of aircraft: over-the-wing and single point pressure. Over-the-wing fueling is like service station fueling of automobiles but without a vapor recovery system. Single point pressure systems use pressure and a closed connection to refuel aircraft. The gasoline vapors in the aircraft tank are vented into the atmosphere through vents on the wings. Other sources of emissions covered by these categories are those from the working and breathing losses that occur during underground storage tank refueling.

6.13.2 Methodology

Point Sources

Point Sources are operations that emit air pollution into the atmosphere at a fixed location within a facility, for which the Air District has issued a permit to operate, e.g., refinery cooling towers. These could also be a collection of similar equipment / sources located across multiple facilities, e.g., reciprocating engines.

During the permit to operate (PTO) issuance process, the BAAQMD collects information from the operating facility and/or determines from published literature, e.g., EPA’s AP-42, characteristics of a source including maximum throughput, emission factors for emitted pollutants, and control factors associated with downstream abatement devices. These characteristics are then stored for future use in the BAAQMD’s internal database. Facilities that hold a permit to operate are required to renew this permit periodically (this period varies based on facility and source type). Upon renewal, the facilities are requested to provide any updates to source characteristics as well as the source throughput for the last 12 months. This throughput, in combination with the emission factors and controls factors stored in the internal database, are used to estimate annual emissions at the source level. These source level emissions are then sorted and aggregated into categories.

Category 80 is a point source category and follows the above methodology for emissions estimates. Category 80 accounts for emissions from refueling of jet engine aircraft with Jet-A fuel.

Area Sources

Categories 79 and 1906 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.

(a) Activity Data / Throughput

For area source categories 79 and 1906, the amounts of aviation gasoline and Jet-A fuel usage at San Jose International Airport (SJC) and Oakland International Airport (OAK) were obtained from the airport Monthly Activity Reports. For some airports fuel usage information was not readily available. The fuel usage at these airports was determined by apportioning the Oakland Airport fuel usage amounts with the relative number of aircraft operations at these airports.

(b) County Distribution / Fractions

Emissions were distributed into the nine counties based on aircraft operations activity at airports in each Bay Area county.

(c) Emission Factors

The uncontrolled emission factors of gasoline service station are used for aviation gasoline refueling with over-the-wing system. The emission factors are chosen based on the Environmental Protection Agency (EPA) document AP-42 and engineering judgment201. Total organic (TOG) emission factors used for categories 79 and 1906 are 21.2 and 0.78 (lbs/1000 gallons), respectively.

Point source emission factors are specific to device and facility as noted in the Methodology section above.

(d) Control Factors

The Air District adopted Regulation 8, Rule 7 in 1992 for pressure-vacuum valve requirement for gasoline dispensing facilities. The Regulation 8, Rule 7 required 95 percent control of fugitive gasoline emissions with an estimated control effectiveness of 9 percent. This control effectiveness provided a net emission reduction of 8.55% during a period of one year (1992-1993).

(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 CARB202 and the US Environmental Protection Agency203.

For category 79, ROG constitutes 95% of TOG.

For category 1906, ROG constitutes 83% of TOG.

For category 80, ROG constitutes 100% of TOG.

Further assessment and improvement of ROG/ TOG speciation profiles has been planned in future inventory updates.

(f) Sample Calculations

The following example shows Category 79 TOG emission calculation for year 2015 for 27,000,000 gallons of aviation gasoline dispensed:

TOG Emissions (tons / day) = Throughput (thousand gallons/year) x Emission Factor (lbs/1000 gallons) x Growth Factor x Control Factor x (ton/ lbs) x (year/days)

TOG Emissions = (27,000) x (21.2) x (1.0) x (0.915) x (1/2000) x (1/365) = 0.717 (tons/ day)

6.13.3 Changes in Methodology

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

6.13.4 Emissions

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

6.13.6 Uncertainties

Uncertainties associated with the emission estimates from aircraft refueling can occur due to malfunctioning of emission control equipment such as the pressure-vacuum valves at the fuel dispensing facilities. Malfunctioning equipment will not efficiently capture evaporated gasoline and can lead to an increase in fugitive TOG emissions.

6.13.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Update: November 06, 2023

6.13.8 References & Footnotes

  1. USEPA. Document AP-42. Compilation of Air Pollutant Emissions Factors. https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors↩︎

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

  3. SPECIATE. USEPA. 2022. https://www.epa.gov/air-emissions-modeling/speciate↩︎

  4. The Federal Aviation Administration (FAA). [accessed 2022 July 14]. https://www.faa.gov/data_research/aviation/taf/↩︎