8.2 Planned Agricultural Burning

Categories 315, 316, 317, 318, and 319

8.2.1 Introduction

Categories 315, 316, 317, 318, and 319 estimate criteria pollutant emissions (particulate, organic, NO_x, SO_x, and CO) and greenhouse gas emissions (Biogenic-CO₂, CH₄, and N₂O) resulting from managed burning of agricultural and forest debris in the San Francisco Bay Area. Categories 315, 316, 317, 318, and 319 account for emissions from open burning of orchard prunings (such as grape vines, apples, and olives), field crops (such as wheat and oats), weeds (such as ditch and canal bank, and marsh burning), range improvement (such as chaparral and grass land burning) and forest debris, respectively.

Carbon Dioxide emissions from these categories are considered biogenic emissions. Biogenic Carbon Dioxide (Bio-CO₂) emissions are a subset of total CO₂ emissions which are emitted from materials that are derived from living cells, excluding fossil fuels, limestone and other materials that have been transformed by geological processes. Bio-CO₂ originates from carbon that is present in materials such as wood, paper, vegetable oils and food, animal, and yard waste. CO₂ and Bio-CO₂ are covered in the greenhouse gas inventory.

8.2.2 Methodology

Categories 315, 316, 317, 318, and 319 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

Annual activity or waste material burn information for these categories was obtained from the District Compliance and Enforcement Division for each county. Emissions were calculated by multiplying the activity (tons/year) for a given category by its composite emission factor (lb/tons).

More details on throughput, county distribution, emission factors and controls is provided in the following subsections.

(a) Activity Data / Throughput

Agricultural waste materials burn activity information for these categories was obtained from the burn permits issued by the District Compliance and Enforcement Division for each county. Annual activity is updated every emissions inventory base year. Agricultural waste materials burn data was provided to the District in various types of units such as acres, tons, pounds, cubic yards, and pile shapes and sizes. By applying crop specific fuel loading factors and other conversion units, all burn activity was converted to tons of material burned per year.

Burning of field crop residue in the Bay Area can vary drastically from year to year due to changes in amounts of crops being grown and changes in means of disposing of the waste. For example, tilling the field versus burning it to dispose of the agricultural vegetation waste materials.

(b) County Distribution / Fractions

Distribution of emissions into counties is based on amounts of material burnt in each county.

(c) Emission Factors

Composite emission factors were developed using crop specific emission factor data from the California Air Resources Board (CARB) and the Environmental Protection Agency (EPA)³³⁶, B. Jenkins’ paper ‘Atmospheric Pollutant Emission Factors from Open Burning of Agricultural and Forest Biomass by Wind Tunnel Simulations’³³⁷, and E.F. Darely’s paper ‘Hydrocarbon Characterization of Agricultural Waste Burning’³³⁸. Background information for emission factors and fuel loading is explained in the California Air Resources Board (CARB) memo, the Agricultural Burning Emission Factors dated August 17, 2000. Emission factors for agricultural burning are generally expressed as pounds of pollutant per ton of material burned. Emission factors for these categories in pounds per ton (lb/ton) are shown below.

(d) Control Factors

There are no applicable control factors for these categories.

(e) Speciation

The ROG/TOG ratios applied to this category or this group of related categories are based on the California Air Resources Board (CARB) Organic Speciation Profiles³³⁹.

For categories 315-318, Organic Speciation Profile number 523, “Open Burning Dump- Landscape/Pruning”, is used for ROG and TOG speciation. ROG constitutes 98.8% of TOG.

For category 319, Organic Speciation Profile number 307, “Forest Fires”, is used for ROG and TOG speciation. ROG constitutes 48.4% of TOG.

The PM_2.5/PM and the PM₁₀/PM ratios applied to this category or this group of related categories are consistent with size fractions of speciation profiles developed by the California Air Resources Board (CARB) and published on their emissions inventory web-page³⁴⁰.

For categories 315-318, PM Speciation Profile number 136, “Agricultural Burning”, is used for PM speciation. PM_2.5 constitutes 94% of total PM and PM₁₀ constitutes 98.6% of total PM.

For categories 315-318, PM Speciation Profile number 916, “Forest Management”, is used for PM speciation. PM_2.5 constitutes 85% of total PM and PM₁₀ constitutes 96% of total PM.

(f) Sample Calculations

The following example shows TOG emission calculation for 2015 for Category 315, Prunings:

TOG Emissions (tons / year) = Throughput (tons / year) x Emission Factor (lbs/ ton) x County Fraction x Growth Factor x Control Factor x (ton/ lbs)

TOG Emissions (tons / year) = 22,500 x 11.69 x 1.0 x 1.0 x 1/2000 = 131.51 (tons/year)

8.2.3 Changes in Methodology

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

8.2.4 Emissions

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

8.2.5 Trends

(a) Historical Emissions / History

The 1981 emissions and amount of agricultural waste materials burned data was used to develop emission factors for base years 1987 and 1990. Prior to base year 2002, historical emission trends were based on Agriculture Dollar Output.

(b) Future Projections / Growth

The growth profile for category 316 was updated using refined historical agricultural waste material burn data obtained from the Air District Compliance and Enforcement Division. This new growth profile reflects historical activity trends for category 316. Emission projections for future years are based on previous five years average activity for each agricultural category.

8.2.6 Uncertainties

Agricultural waste materials burn data was provided to the District in various types of units such as acres, tons, pounds, cubic yards, and pile shapes and sizes. Uncertainties may exist in agricultural waste material amount estimations and reporting inaccuracies.

8.2.7 Contact

Author: Sukarn Claire

Reviewer: Ariana Husain

Last Update: November 06, 2023

8.2.8 References & Footnotes