9.16 Agricultural Aircraft

Category 711

9.16.1 Introduction

Considered in category 711 are criteria pollutant emissions (particulate, organic, NOx, SOx, and CO) from agricultural aircraft engines during aerial spraying operations on agricultural crops in the San Francisco Bay Area. Only combustion products from the aircraft engine during spraying are estimated in this category. This does not include emissions from materials sprayed, which are inventoried under pesticide category.

The aircraft involved are usually piston engine type aircraft. The most common agricultural aircraft are fixed wing, but helicopters are also used. In the aircraft piston engine, mixture of fuel and air are burned from which energy is extracted by a piston and crank mechanism driving a propeller.

9.16.2 Methodology

Category 711 is considered an area source category since it covers 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.

Fuel consumption by agriculture aircraft in the Bay Area was estimated based on number of acres sprayed and fuel used per acre. The information on estimated number of acres sprayed was obtained from the county agricultural crop reports for 1996. Total acreage for field, vegetable, fruit, nut, and nursery crops were used in estimating a District total of 178,705 acres sprayed.

An average fuel consumption of 0.1053 gal per acre sprayed was used based on the California Air Resources Board (CARB)414 report on the total number of acreage sprayed in California and total statewide fuel usage. From this information, an estimated total fuel usage was derived:

\[ \text{Total fuel usage} = 0.1053\ \text{gal/acre} \times 178,705\ \text{acre} = 18,818\ \text{gal} \]

(a) Activity Data / Throughput

The information on estimated annual number of acres sprayed was obtained from the county agricultural crop reports for the Bay Area.

(b) County Distribution / Fractions

County activity distribution was based on reported total crop acreage for each county.

(c) Emission Factors

Emission factors were derived based on the U.S. Environmental Protection Agency (EPA) document AP-42415 for a Lycoming 0-320 and Continental 0-200 aircraft engines. Only the takeoff mode was considered, assuming the aircraft would be at a similar power mode during spraying operations.

The fuel specific greenhouse gas emission coefficients for this category were obtained from the U.S. Department of Energy’s (DOE) Energy Information Administration (EIA)416, the EPA document AP-42, and the California Air Resources Board (CARB).

(d) Control Factors

No emission controls have been implemented by the Air District for this category.

(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 CARB417 and the US Environmental Protection Agency418. For this category or group of categories, ROG constitutes 98% 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 CARB419 or the US Environmental Protection Agency. For this category or group of categories, PM2.5 constitutes 100% of total PM and PM10 constitutes 100% of total PM. The Air District staff routinely review speciation profiles and may update ratios as needed for improving emissions estimates.

(f) Sample Calculations

\[ \ \text{TOG Emissions} = 18,818\ \text{gal/yr} \times 76.979\ \text{lb/1000 gal} \div 365\ \text{day/yr} \div 2000\ \text{lb/ton} = 0.002\ \text{ton/day}\ \text{TOG} \]

9.16.3 Changes in Methodology

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

9.16.4 Emissions

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

9.16.6 Uncertainties

This methodology uses emission factors that were developed in the 1990s. It is assumed that these emission factors are applicable to the aircraft currently in use for agricultural aerial applications. The review and redevelopment of aircraft emission factors may lead to more accurate emission estimations for this category.

9.16.7 Contact

Author: Sukarn Claire

Reviewer: Minh Nguyen

Last Update: November 06, 2023

9.16.8 References & Footnotes

  1. The California Air Resources Board (CARB). [accessed 2022 Nov 14]. http://ww2.arb.ca.gov/homepage↩︎

  2. USEPA. 1995. AP-42. Compilation of Air Pollutant Emissions Factors. https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors↩︎

  3. The Energy Information Administration (EIA). [accessed 2022 Nov 8]. https://www.eia.gov/energyexplained/natural-gas/use-of-natural-gas.php↩︎

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

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

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