Amimal Feeding Operations

Animal feeding operations (AFOs) are an important source of atmospheric ammonia (NH3), methane (CH4) and nitrous oxide (N2O). The gas emissions can occur in feeding lot, waste storage/treatment and manure field application. Monitoring of air emissions and soil leaching from AFOs is essential for preserving local air and water quality, especially since such processes are largely driven by biological activity and local meteorological conditions with significant variability over time, space, and management practices. This complexity results from the interaction of a suite of biogeochemical processes such as decomposition, nitrification, denitrification, fermentation, and ammonia volatilization. The use of the constant emission factor approach has proven to be insufficient for quantifying the gas emissions from livestock housing, manure storage, or manure/fertilizer application in field (NRC 2003).



Assessing the environmental impact of manure management is difficult due to high variability in the quality and quantity of animal waste, and in the numerous factors affecting the biogeochemical transformations of manure during storage, treatment and field application. There is an urgent need for scientifically sound, mass balance based, process models for quantifying air emissions from animal feeding operations. Measurement programs are essential, but must be supplemented by process-oriented modeling that incorporates mass balance constraints to extrapolate in both space and time. The time is right for moving beyond the current and yet inadequate emission factor approach by developing process based models for quantifying air emissions from animal feeding operations. In collaboration with UNH, University of California at Davis, and California State University Fresno, AGS is developing a process-based decision support tool for estimating air emissions from animal feeding operations. Advantages to developing process-based models for estimating emissions from the combined components (housing, manure collection, handling and storage systems, land application) of dairies: True process-based models do not rely on constant emission factors. They assess the impact on emissions of varying conditions (e.g., climate, storage facility, soils). These models will continue to improve as more field studies are conducted and published, and they do not obviate the need for a strong measurement program. By enforcing a mass balance in the model (i.e., conservation of mass), the sum of all emission factors are constrained to be = 100% of inputs. This is both good bookkeeping and essential for evaluating trade-offs in mitigation strategies. Full system analysis with dynamic, process-based models can inexpensively and efficiently evaluate mitigation scenarios under various conditions, and can help target mitigation toward facility component(s) and/or operation(s) that cause the greatest emissions. Simultaneously provide estimates of all emissions for comprehensive assessments of mitigation efforts.



Environmental Protection Agency (EPA) Air Quality Compliance Agreement 2005 for Animal Feeding Operations requires livestock facilities to

Reduce air pollution
Ensure compliance with applicable Clean Air Act, Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) and Environmental Planning and Community Right-to-Know Act (EPCRA) provisions
Monitor and evaluate AFO emissions
Promote a national consensus on methodologies for estimating emissions from AFOs
Report any qualifying releases of ammonia (NH3) and hydrogen sulfide (H2S) as required by section 103 of CERCLA and section 304 of EPCRA

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