Gaseous Emissions From Cattle Feedyards and Dairies: An Overview.

Concentrated animal feeding operations (CAFO) such as cattle feedyards and dairies are sources for several gases, including methane, nitrous oxide, ammonia, hydrogen sulfide, and volatile organic compounds. Methane and nitrous oxide are potent greenhouse gases that contribute to global warming and consequent climate disruption. Ammonia is a reactive nitrogen compound that can overfertilize and negatively impact terrestrial and aquatic ecosystems. Hydrogen sulfide and volatile organic compounds can contribute to local nuisance malodors. How a CAFO is managed can have a large effect on the magnitude of emissions. Important management variables include type of housing, diet composition, manure handling, and emission abatement strategies. Abatement and mitigation of gaseous emissions are especially challenging, with the nexus of effectiveness and reasonable cost often difficult to achieve. There is a wide range of methods and technologies to quantify emissions. Choice of a methodology depends on factors such as scale of measurement, compound of interest, and purpose of measurement, recognizing that each method holds advantages and disadvantages. Noninterference micrometeorological approaches are often appropriate for whole farm measurements, and have also been effectively used at smaller scales, such as manure stockpiles and manure field applications. Interference methods, including closed chamber techniques, are generally appropriate to quantify relative differences and to compare treatments. Chamber methods range from periodic air sampling of small enclosures placed on an emitting surface to large, continuously sampled chambers that hold several animals. Greater understanding of the physical, chemical and biological processes that control emissions has informed the development of process models of emissions. Accurate process models will help to identify key points of emission abatement, assess the effects of changing management strategies on emissions, and develop accurate emissions inventories.