Identifying Methane Emissions from Animal Feeding Operations in a Mixed Emission Region Within the Colorado Front Range 

K.M. Steinmann¹, M.E. McCabe¹, J.F.J. Calahorrano², A. Sullivan², I.B. Pollack², E.V. Fischer² and D.R. Caulton¹

¹University of Wyoming, Laramie, WY 82071; 307-766-3245, E-mail: ksteinma@uwyo.edu
²Colorado State University, Department of Atmospheric Science, Fort Collins, CO 80523

Agriculture and oil and natural gas (ONG) production are two of the largest sources of methane (CH₄) emissions in the U.S and are often found near each other, like in the northern Colorado Front Range (NCFR), making CH₄ source attribution difficult. Using data from the Transport and Transformation of Ammonia (TRANS²Am) campaign, we separate CH₄ emissions related to agriculture from other sources, like ONG production. Phase one of the TRANS²Am campaign consisted of 15 research flights during August 2021 over the NCFR (Figure 1 shows the flight path for RF 13). CH₄, ammonia (NH₃), and ethane (C₂H₆) concentrations were measured using the University of Wyoming King Air (UWKA) research aircraft, which circled concentrated animal feeding operations (CAFOs) housing sizable beef and dairy cattle populations. Two different approaches were used to differentiate CH₄ emissions by source. The first approach removed the CH₄ associated with ONG by subtracting an amount of CH₄ based on the C₂H₆:CH₄ ratio. The second approach estimates the CH₄ emissions from CAFOs using multivariate regression (MVR), incorporating the NH₃ concentration and NH₃:CH₄ ratio. These two approaches were used to calculate CH₄ emissions from CAFOs sampled during the first phase of the TRANS²Am campaign. We have found that our calculated CAFO CH₄ emissions are slightly higher than those of previous studies and the EPA’s National Emission Inventory estimate for beef cattle. This research shows the importance of correctly attributing CH₄ emission sources to properly represent CH₄ sources in inventories and to better understand the role of livestock emissions on the atmosphere and climate.

Figure 1. Path of TRANS²Am RF 13, colored by CH₄ (ppbv). Black numbers represent the corresponding transect number. Animal operations are indicated by the different colored circles as in Figure 1. Green dots represent ONG wells, data of ONG as of 2015 (Colorado Department of Natural Resources Oil & Gas Conservation Commission).