10.8 Animal Waste, Livestock

Categories 2333 - 2346

10.8.1 Introduction

Categories 2333 - 2346 account for organic emissions (TOG and ROG) from livestock and cattle in the form of methane (CH4) emissions. Livestock emissions include CH4 from enteric fermentation (microbial decomposition of food in ruminant animals, and CH4 and particulate matter (PM) from ongoing manure management processes in animal farms. Emissions are only accounted for domesticated cattle. The cattle classes include dairy cattle, range cattle, sheep, horses, and goats, swine, and various types of poultry including turkeys. These emissions are directly related to animal population and the emission factors of various animal classes.

Emissions are classified under the following category numbers:

Category # Description
2333 Dairy Cattle - Enteric Fermentation
2334 Range Cattle - Enteric Fermentation
2335 Sheeps - Enteric Fermentation
2336 Goats - Enteric Fermentation
2337 Horses - Enteric Fermentation
2338 Dairy Cattle - Manure Management
2339 Range Cattle - Manure Management
2340 Sheeps - Manure Management
2341 Goats - Manure Management
2342 Horses - Manure Management
2343 Swine - Manure Management
2344 Broilers - Manure Management
2345 Turkeys - Manure Management
2346 Layers and Pullets - Manure Management

10.8.2 Methodology

The methodology to estimate livestock emissions is presently based on California Air Resoures Board’s (ARB) methodology which is derived from U.S. Environmental Protection Agency’s inventory document457. These categories fall under the class of area sources as emissions are based on aggregated populations over all farms, as opposed to emissions from individual farms. For each category, the emissions are calculated by multiplying the emission factor and population of each animal type.

(a) Activity Data / Throughput

All available animal population data is based on two sources. The first source is ARB’s GHG inventory data query tool458 which provides California statewide animal population data. This in turn is derived from the second source used for this documentation work, which is U.S. Department of Agriculture National (USDA) Agricultural Statistics Service year 2017 Census of Agriculture459. The USDA datasets are used to derive data for all animal classes at the county-level for year 2017. Statewide data for California was reported to USDA for the 2017 census by the California Department of Food and Agriculture’s (CDFA) Agricultural Resources Directory. Cattle data is available from these sources at a higher granularity e.g. livestock cattle population data is available for calves, cows, beef cows, 0-12 months, 12-24 months, heifer, steer, bulls etc.; but for the purpose of this inventory reporting, data is aggregated into two animal classes - dairy livestock and range cattle. The year 2017 county-specific USDA data is used in combination with ARB state-level animal population data to derive county-specific animal populations for years 2011-15, with the assumption that the population ratios remain constant.

(b) County Distribution / Fractions

The USDA year 2017 census is used to derive county-specific animal population data for each emissions category. These county-specific populations are used to derive relative county fractions for each category (that is held constant during this time) and used for deriving county-specific emissions for years 2011-15.

Throughputs / activity data for Solano and Sonoma county are apportioned to the San Francisco Bay Area (SFBA) as per their land area portions within the District’s jurisdiction which comes to be 48% and 39%, respectively.

(c) Emission Factors

Emission factors for various animal classes are based on CARB GHG inventory2 which in turn are derived from Intergovernmental Panel for Climate Change’s guidance documents460.

For enteric fermentation, weighted emission factors are calculated for dairy cows and range cattle respectively by combining emission factors for sub-classes (e.g. heifer feedlots, bulls, 0-12 month dairy etc.) with their respective populations in California (see (f)Sample Calculations). For manure management, emission factors are derived by combining the ratio of total California manure management and enteric fermentation CH4emissions (from2) with the weighted emission factor for enteric fermentation derived above. The California-specific emission factors are applied for SFBA as well.

For manure management processes, TOG emission factors are additionally available from CARB non-cattle livestock husbandry. PM emission factors are only considered for cattle livestock.

(d) Control Factors

Presently, no specific District regulations or controls have been instituted to reduce livestock (CH4) emissions in the SFBA. There are certain District regulations aimed at particulate matter and ammonia emissions in agriculture-heavy Districts like the San Joaquin Valley Air Pollution Control District (SJVAPCD).

(e) Speciation

All livestock related emissions for enteric fermentation source-type are CH4 and are hence considered non-reactive. Subsequently the ROG / TOG ratio is considered negligible or zero for categories 2333-37. For manure management processes (categories 2338-46), the CARB assumption of ROG / TOG = 0.08 is used. Thus, reactive organic gases (ROG) are also calculated and accounted for within the TOG emissions in the manure management categories. CARB’s Livestock Dust Operation speciation profile # 423 is used for PM emissions apportionment to derive PM10 and PM2.5 emissions.

(f) Sample Calculations

Example 1: Calculate the CH4 emission factor for enteric fermentation for dairy cows category in California given:

  1. the CH4 emission factor for calves is = 25.6 lbs CH4/head/year,
  2. the CH4 emission factor for cows is = 322.6 lbs CH4/head/year,
  3. the CH4 emission factor for 0-12 months is = 95.8 lbs CH4/head/year,
  4. the CH4 emission factor for 12-24 months is = 144.7 lbs CH4/head/year, and,
  5. the California populations of calves is 886,202; cows is 1,731,338; 0-12 months is 216,808; and 12-24 months is 510,080.

\[ \begin{eqnarray} \text{CH}_{4}\ \text{E.F.} &=& (\frac{25.6\ lb}{head \cdot yr}\times 886202\ head   \ &+& \frac{322.6\ lb}{head \cdot yr}\times 1731338\ head &+& \frac{95.8\ lb}{head \cdot yr}\times 216808\ head \\ &+& \frac{144.7\ lb}{head \cdot yr}\times 510080\ head) &/& sum\ of\ all\ populations\ \\ &=& 202\ lb/head\ \text{CH}_{4}\\ \end{eqnarray} \]

Example 2: Calculate the CH4 emission factor for manure management for dairy cows category in California given:

  1. the weighted CH4 emission factor for dairy livestock is = 202 lbs CH4/head/year,
  2. the enteric fermentation CH4 emissions for dairy livestock = 305,813 metric tonnes CH4/year, and,
  3. the manure management CH4 emissions for dairy livestock = 395,610 metric tonnes CH4/year

\[ \begin{eqnarray} \text{CH}_{4}\ \text{E.F.} &=& \frac{202\ lb}{head \cdot yr}\times \frac{395610\ tonnes}{305813 \ tonnes}\ \\ &=& 261.4\ lb/head\ \text{CH}_{4}\\ \end{eqnarray} \]

10.8.3 Changes in Methodology

Emissions under this broader section used to be represented under a different set of categories (1619 through 1627) in the past inventories (e.g. base year 2011 inventory). When the Air District developed its most recent GHG emissions inventory in 2017, the methodologies for these sources, category classification scheme and activity data sources were all aligned with CARB’s GHG inventory efforts for the same emission classes. Consequently, new emission categories were developed to represent these categories and to align future calculations with the scope of equivalent CARB categories.

The approach to calculate weighted emission factors for enteric fermentation and manure management is different from previous inventory efforts. County-data is directly derived from USDA3 which is also a change from the previous inventory. PM emission factors are included for the first time with certain cattle husbandry operations.

10.8.4 Emissions

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

Cattle livestock categories (dairy cows and range cattle) are amongst the biggest emitters of TOG within this broader family of categories (both enteric fermentation and manure management) accounting for ~6000 - 9000 tons/year of TOG emissions in year 2015. Catgories 2333, 2334, 2338 and 2339 together account for ~30,000 tons of TOG in year 2015. Category 2339 (manure management - range cattle) is an important source of PM with over 1000 tons of emissions annually.

10.8.6 Uncertainties

The main source of uncertainties in this documentation are the representativeness of the emission factors derived from IPCC sources3 for California husbandry and more specifically to Bay Area’s agricultural practices. A +/-30-50% uncertainty is prescribed by IPCC in the calculations owing to the use of the more generalized emission factors. The USDA census numbers are ultimately self-reported and there could be significant uncertainties in the population estimates of certain animal categories although cattle livestock groups are quite well-quantified in California. IPCC recommends an uncertainty of +/-20% in the animal population throughputs in developed countries. A conservative combined uncertainty bound, which is the square-root of the linear sum of squared standard uncertainty components, of +/- 55% should be assumed in the emissions estimates.

10.8.7 Contact

Author: Abhinav Guha

Reviewers: Tan M. Dinh and Yuan Du

Last Update: November 06, 2023

10.8.8 References & Footnotes

  1. USEPA. 2013. https://www.epa.gov/sites/default/files/2015-12/documents/us-ghg-inventory-2013-annexes.pdf↩︎

  2. CARB. 2021. California 2000-2019 GHG Inventory. https://ww2.arb.ca.gov/applications/california-ghg-inventory-documentation↩︎

  3. USDA. 2019. USDA National Agricultural Statistics Service, 2017 Census of Agriculture. https://nass.usda.gov/AgCensus↩︎

  4. IPCC. 2006. 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston HAS., Biennia L., Miwa K., Negara T. and Tanabe K. (eds), Vol.4, Chap. 10: Livestock and Manure Management. Published: IGES, Japan. http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_Volume4/V4_10_Ch10_Livestock.pdf↩︎

  5. ABAG. 2019. Plan Bay Area 2040. Association of Bay Area Government (ABAG). http://2040.planbayarea.org/reports↩︎