10.2 Farming Operations

Categories 749 and 1435

10.2.1 Introduction

Categories 749 and 1435 account for particulate matter (PM) emissions from agricultural activities. Farming Operations consist of two categories - Agricultural Land Preparation (Category 749) and Agricultural Harvest Operations (Category 1435). The methodology for emission calculation for both these categories are based on California Air Resources Board (ARB) methodology documents431, 432.

Category 749 accounts for PM emissions generated by farming operations such as tilling, plowing, discing, leveling, etc. These activities are normally performed in the early spring months, and hence temporal distribution across the year is highly skewed. Particulate emissions from agricultural tilling are highly dependent on type of crop, climate, soil properties and equipment characteristics.

Category 1435 accounts for PM emissions caused from harvest activities. These activities include harvest vehicles traveling over the soil, mechanical processing of crop and underlying soil, or removal of crop waste material through blowing or sweeping action. These activities are normally performed in the fall months, and hence temporal distribution across the year is highly skewed.

Emissions from agricultural land preparation and harvesting typically occur as process emissions in different centers of activity across each farm, and are considered area source emissions. The unique nature of aggregating crop-specific activity data at the county level and calculating the PM emissions for both these categories leads to a Special Case designation in the emissions inventory computation process (see Methodology).

Emissions from fuel combustion of agricultural equipment, such as mowers, tractors, tillers, etc., are accounted for in Category 1655, Category 1656 and Category 1646 in Chapter 9.3 (Agricultural Equipment) of this report .

10.2.2 Methodology

Categories 749 and 1435 are considered as Special Cases from a computational point of view. Emissions estimates are based on CARB emission factors and county-level acreage data which vary by crop, year and county. Emission calculation has to be performed for each crop, county and year as the acreage devoted to crops and the crop-specific emission factors can vary from year to year. Each crop’s land preparation and harvesting emissions are estimated in this manner and then summed up respectively for the total county level PM10 emissions.

(a) Activity Data / Throughput

Year-specific acreage data for the years 2011-2015 for each county in the San Francisco Bay Area (SFBA) can be accessed from the Annual County Crop Reports for all nine counties433 434 435 436 437 438 439 440 441.

(b) County Distribution / Fractions

The PM emissions for each county are calculated separately and the relative ratio of emissions between the nine counties is used to determine the county fractions. Only a portion of emissions for Solano (38%) and Sonoma (32%) counties are included in the regional emissions total as these percentages represent the proportion of land area within these counties that is included in the BAAQMD’s jursidiction.

(c) Emission Factors

The crop specific PM10 emission factors are calculated by multiplying a land preparation emission factor (i.e. root cutting, discing, rippling, weeding, land planning, etc.) with the number of passes performed per acre that are needed to prepare a field for planting a particular crop (acre-pass). A crop may have multiple land preparation operations with its corresponding number of acre-passes. In this case, the crop specific emission factor is the sum of acre-pass weighted emission factor for each land preparation operation.

For land preparation, there are 20 crop specific PM10 emission factors (see Table 2.a1) that include such crops as alfalfa, almonds, garlic, grapes (raisin, table and wine), tomatoes, wheat, etc. All other crops are assigned an emission factor from one of the 20 crop specific PM10 emission factors (see Table 31).

For harvesting, the PM10 emission factors are taken from Table A and B of ARB’s Agricultural Harvest Operations document2. Using the PM10 emissions factors for cotton, almonds, and wheat as a baseline, other crop’s PM10 emission factors are estimated.

(d) Control Factors

Presently, no known District or state-level regulations or controls have been instituted to reduce PM emissions from agricultural operations.

(e) Speciation

Particulate emissions are calculated as PM10 emissions. CARB’s Agricultural Tillage Dust Speciation profile # 417 is applied to estimate PM2.5 and total PM emissions. Total PM emissions are calculated by dividing PM10 value by 0.4543, while PM2.5 emissions are 6.81% of PM emissions.

(f) Sample Calculations

Example 1: Calculate the 2010 PM10 and total particulate emissions from land preparation activities for garlic in Santa Clara County, where

  1. the crop specific PM10 emission factor = 6.5 lbs PM10/acre/yr,
  2. 366 acres were devoted to garlic in 2010, and
  3. the PM10 factor (ratio of PM10/PM) is .4543.

\[ \begin{eqnarray} \text{PM}_{10}\ \text{emissions} &=& \frac{6.5\ lb}{acre \cdot yr}\times 366\ acre \\ &=& 2379\ lb/yr \\ &=& 1.19\ ton/yr\ \text{PM}_{10} \end{eqnarray} \]

\[ \begin{eqnarray} \text{PM emissions} &=& 1.19\ ton/yr\ \text{PM}_{10} \div 0.4543 \\ &=& 2.62\ ton/yr\ \text{PM} \end{eqnarray} \] Example 2: Calculate the 2010 PM10 and total particulate emissions from agricultural harvest operations for walnuts in Contra Costa County, where

  1. the Crop specific PM10 emission factor = 40.77 lbs PM10/acre/yr,
  2. 399 acres were devoted to walnuts in 2010, and
  3. the PM10 factor (ratio of PM10/PM) is .4543.

\[ \begin{eqnarray} \text{PM}_{10}\ \text{emissions} &=& \frac{40.77\ lb}{acre \cdot yr}\times 399\ acre \\ &=& 16267\ lb/yr \\ &=& 8.13\ ton/yr\ \text{PM}_{10} \end{eqnarray} \]

\[ \begin{eqnarray} \text{PM emissions} &=& 8.13\ ton/yr\ \text{PM}_{10} \div 0.4543 \\ &=& 17.90\ ton/yr\ \text{PM} \end{eqnarray} \]

10.2.3 Changes in Methodology

The methodology to estimate emissions for agricultural land preparation and harvesting has remained the same since the last iteration of the Air District’s inventory (base year 2011). The emissions are based on reported activity data from years 2011 through 2015 with emissions forecasted to year 2040, and backcasted to 1990.

10.2.4 Emissions

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

For agricultual land preparation, the PM emissions for base year 2015 in the Bay Area total to ~833 tons/year, of which 32% come from the portion of Solano county in SFBA, about a quarter from Contra Costa county, and about 20% from Santa Clara county.

For agricultural harvesting, the PM emissions for base year 2015 in the Bay Area total to ~445 tons/year, of which the majority of emissions (~75%) arise in the Solano county. Most of the Solano county emissions are attributed to harvesting of walnuts and almonds.

The PM emissions from the two categories show negligible variation across the five years (2011-2015) since crop acreage is a reasonably constant quantity on a year to year basis.

10.2.6 Uncertainties

The main source of uncertainties in the PM emissions reported in Categories 749 and 1435 stem from the uncertainties in how the crop-specific emissions factors are derived and how many of them are based on repeat observations and calculations. Since many of the crop-specific emission factors are scaled and developed from a few of them (which are based on calculations), there could be large uncertainty in those emission factors. Crop-acreage is a much more precise and well-documented variable, with each county producing annual reports accounting for their land use. Keeping these factors in mind, it would be safe to assume that the PM estimates derived using this methodology can be improved without a more refined and well-quantified estimate of emission factors covering a wide variety of crops.

10.2.7 Contact

Authors: Abhinav Guha and Stephen Reid

Reviewers: Tan M. Dinh and Yuan Du

Last Update: November 06, 2023

10.2.8 References & Footnotes

  1. California Air Resources Board. 2003a. Areawide Sources, Section 7.4, Agricultural Land Preparation, revised January 2003. http://www.arb.ca.gov/ei/areasrc/fullpdf/full7-4.pdf.↩︎

  2. California Air Resources Board. 2003b, Areawide Sources, Section 7.5, Agricultural Harvest Operation, revised January 2003. http://www.arb.ca.gov/ei/areasrc/fullpdf/full7-5.pdf.↩︎

  3. Alameda County Annual Crop Reports. Various Years. https://www.acgov.org/cda/awm/resources/stats.htm↩︎

  4. Contra Costa County Annual Crop Reports. Various Years. https://www.contracosta.ca.gov/2207/Crop-and-Economic-Reports↩︎

  5. Marin County Annual Crop Reports. Various Years. https://www.marincounty.org/depts/ag/crop-reports↩︎

  6. Napa County Annual Crop Reports. Various Years. https://www.countyofnapa.org/Archive.aspx?AMID=39↩︎

  7. San Francisco County Annual Crop Reports. Various Years. https://www.sfdph.org/dph/EH/Agriculture/↩︎

  8. San Mateo County Annual Crop Reports. Various Years. https://agwm.smcgov.org/agricultural-crop-report↩︎

  9. Santa Clara County Annual Crop Reports. Various Years. https://www.sccgov.org/sites/ag/news/Pages/2010-2019.aspx↩︎

  10. Solano County Annual Crop Report. Various Years. https://www.solanocounty.com/depts/agriculture/crop_report/2009_2018.asp↩︎

  11. Sonoma County Annual Crop Reports. Various Years. https://sonomacounty.ca.gov/Agriculture-Weights-and-Measures/Crop-Reports/↩︎