A Review of Ammonia Emissions from Confined Swine Feeding Operations

Ammonia emissions from swine feeding operations depend on the housing type; animal size, age, and type; manure management, storage, and treatment; climatic variables; and manure utilization or land application techniques. Techniques or methods for estimating or quantifying NH3 flux from a source to the atmosphere include nitrogen mass balance, micrometeorology, flux chambers, models, and emission factors. Of these techniques, emission factors, once established, provide the most convenience in estimating emissions. However,it is important to understand how a particular emission factor is determined and whether it accurately reflects a composite or average emission for all the variable conditons. Using an average ammonia emission factor multiplied by pig inventory to determine a regional or national ammonia emission inventory may be misleading, especially in the U.S. where existing emission factors were developed using data from swine facilities in Western Europe. Housing, manure management practices, and climate vary among different regions of the U.S. and can be very different from those in Western Europe. In addition, ammonia concentrations and emission estimations have been determined with a variety of methods, making it difficult to compare results. To determine representative ammonia emissions from confined swine feeding operations, it is important that emission factors be specific enough to account for animal type and size, housing system, manure storage and treatment, land application, and climatic effects. This article describes the strengths and limitations of emission factors as currently used and provides recommendations for determining realistic ammonia emission factors for swine feeding operations. Because of the limited nature of the data published in the literature, emission factors for different animal management systems could not be presented. Regulators, consultants, cooperative extension personnel, and other leaders in the agricultural community with interest in ammonia emissions should be aware of the lack of reliable U.S. data available for calculating accurate emission factors. The scientific research community should standardize methods for measurement, calculation, and reporting of ammonia emissions.