2017 News & Events

Characterizing Emissions From Animal Feedlots

20 April 2017

feedlot aerial
A feedlot in northeastern Colorado. Photo: D. Bon

A team of scientists from CSD and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder published a paper in Atmospheric Chemistry and Physics that characterizes the emissions from animal feedlots.

Scientists have long known that animal feedlots emit volatile organic compounds (VOCs) into the atmosphere. This is problematic because VOCs can react to form ozone and fine particles, affecting air quality and human health. Furthermore, these VOCs are responsible for the unpleasant odor from animal feedlots.

However, it wasn't well-understood how different activities within the feedlots contribute to VOC emissions – for example, to what extent emissions come from the animals and their waste, or from the storage and use of the feed. CSD scientists also looked to characterize the chemical composition of those VOCs specific to animal feedlots, which included a broad category of chemicals such as alcohols, carboxylic acids, and sulfur compounds.

NOAA ESRL CSD mobile lab van at feedlot
The CSD van, outfitted with instruments to take measurements of methane, nitrous oxide and ammonia. Photo: J. Peischl, NOAA / CIRES

To better understand the sources and chemical compositions of the VOC emissions, CSD scientists made measurements from both their mobile laboratory and the NOAA WP-3D research aircraft. A new instrument on the aircraft and mobile laboratory allowed the scientists to get fast, high-resolution measurements of many different VOC chemicals as they sampled downwind from the feedlots.

The researchers looked at different kind of facilities and examined the chemical signatures of the VOCs and ammonia they emitted. The results show that VOC emissions mainly come from two sources: animals and their waste or feed storage and handling. However, the composition of what each source emits is different. For example, animals and their waste emit phenols and nitrogen-containing compounds such as ammonia, while the feed emits alcohols, carboxylic acids, and sulfur-containing compounds.

The researchers found that the same animals (cows) give off different VOCs depending on their diet and other practices. For example, across the Front Range, beef cattle had higher levels of emissions than dairy cattle. Also, there are sometimes complaints of unpleasant smells near large animal feedlots. The researchers found that sulfur-based compounds were the primary source of feedlot odor for all types of animal feedlots, and these sulfur compounds are largely emitted by animal waste.

Industry practices (e.g. feed additives) affect odor and atmospheric chemistry in and around feedlots. These results suggest that a better understanding of these processes – the sources and chemical composition of VOCs – could help industry target specific compounds and mitigate the impacts of emissions on air quality and human health, without affecting the productivity of the industry.

Yuan, B., M.M. Coggon, A.R. Koss, C. Warneke, S. Eilerman, J. Peischl, K.C. Aikin, T.B. Ryerson, and J.A. de Gouw, Emissions of volatile organic compounds (VOCs) from concentrated animal feeding operations (CAFOs): chemical compositions and separation of sources, Atmospheric Chemistry and Physics, doi:10.5194/acp-17-4945-2017, 2017.


Concentrated animal feeding operations (CAFOs) emit a large number of volatile organic compounds (VOCs) to the atmosphere. In this study, we conducted mobile laboratory measurements of VOCs, methane (CH4) and ammonia (NH3) downwind of dairy cattle, beef cattle, sheep and chicken CAFO facilities in northeastern Colorado using a hydronium ion time-of-flight chemical-ionization mass spectrometer (H3O+ ToF-CIMS), which can detect numerous VOCs. Regional measurements of CAFO emissions in northeastern Colorado were also performed using the NOAA WP-3D aircraft during the Shale Oil and Natural Gas Nexus (SONGNEX) campaign. Alcohols and carboxylic acids dominate VOC concentrations and the reactivity of the VOCs with hydroxyl (OH) radicals. Sulfur-containing and phenolic species provide the largest contributions to the odor activity values and the nitrate radical (NO3) reactivity of VOC emissions, respectively. VOC compositions determined from mobile laboratory and aircraft measurements generally agree well with each other. The high time-resolution mobile measurements allow for the separation of the sources of VOCs from different parts of the operations occurring within the facilities. We show that the emissions of ethanol are primarily associated with feed storage and handling. Based on mobile laboratory measurements, we apply a multivariate regression analysis using NH3 and ethanol as tracers to determine the relative importance of animal-related emissions (animal exhalation and waste) and feed-related emissions (feed storage and handling) for different VOC species. Feed storage and handling contribute significantly to emissions of alcohols, carbonyls, carboxylic acids and sulfur-containing species. Emissions of phenolic species and nitrogen-containing species are predominantly associated with animals and their waste.