Greenhouse Gas Emissions From Agriculture and Animal Operations: Influencing Factors, Measurement Limitations, and Potential Mitigation Strategies.

Gas emissions from anthropogenic sources significantly contribute to degradation of environmental quality, adversely impact human health, and are potential factors for global climate change. Agricultural operations, including animal feeding operations, are major producers of greenhouse and other regulated gases. Major gases of concern include carbon dioxide, methane, ammonia, nitrous oxide, nitrogen oxides, and hydrogen sulfide, as well as volatile organic compounds. These gases not only drive climate change processes through greenhouse effects, but also increase atmospheric degradation, odor pollution, and a wide range of human and animal health hazards. Accurate quantification of gas emission from agricultural sources, such as fertilized soils, biomass burning, manure production, and manure handling systems, is extremely difficult due to a plethora of complicating factors. Variations in soil characteristics influence physical, chemical, and biological processes that produce gases; these processes also vary spatially and temporally. Gas emission from animal sources, fluctuate depending on species of animal, production efficiency, type of feed, time of day, temperature, season, wind speed, manure handling, and manure storage. The known complexity of emission characteristics and confounding factors makes reliable emission measurements difficult. Expansion of large-scale agricultural and animal operations necessitates monitoring of emissions and eventual regulation. However, environmental monitoring strategies have often been instituted on the basis of emissions factors, a number based on relatively simplified data inputs including animal numbers. These emission factors may be grossly inaccurate in many situations. In an effort to consolidate data for monitoring emissions more consistently, a thorough analysis of known emissions, measurements and models encompassing a full range of climatic conditions, animals systems, and measurement methodologies has been conducted. Accurately quantifying and monitoring agricultural gas emission is a first step towards successful mitigation strategies for both greenhouse gases and pollutants and towards effective risk management strategies.