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Agricultural activities, livestock production in particular, have been reported to be the largest contributor of ammonia emissions into the atmosphere. Farm animals consume a considerable amount of protein and other nitrogen (N) containing substances with their feed. The conversion of the dietary N to animal product is often inefficient and 50 to 80 % of the N consumed is excreted. Ammonia is produced as a consequence of bacterial activity involving the excreted organic N substrates. Ammonia can be emitted from animal housing, manure storage and treatment facilities and manure land application in animal production operations. Factors that affect ammonia volatilization include source characteristics (manure, building type, storage and treatment methods, and land application method), pH, temperature, wind speed, and surface characteristics. Building emissions range from 0.8-6.1, 0.14-1.77, and 0.6-9.3 g NH3/h-AU (1 AU=500 kg live weight) for pigs, dairy cattle and poultry, respectively. Storage/treatment losses are reported to be 0.3 9.0 g NH3-N/m 2 /day. Land application losses range from 14-83%, 6-47%, and 0-7% of total ammonia nitrogen applied for surface spread, band spread and injected manure, respectively. Emission factors are reported as kg NH3/yr/animal and include buildings, manure storage/treatment, and land application emissions. Emissions factors are based on average annual conditions. Emission factors currently used in the U.S.A. are based on those developed for Europe. Currently, research is in progress to determine ammonia emissions in the U.S. (there are conference proceedings where ammonia emission measurement results from animal production facilities have been reported and indications that some of these papers have been submitted for journal publication). Emission factors in Europe are 15-23.5, 2.3-7.6 and 0.22 kg NH3-N/animal-yr for dairy, swine and poultry, respectively. The corresponding emission factors in the U.S. are 19, 7.6 and 0.18 kg NH3-N/animal-yr for dairy, swine and poultry, respectively. Some empirical and mechanistic models have been published for ammonia emission in buildings and from storage/treatment facilities and land application. Most of the empirical models use statistics to obtain correlations and relationships between factors that affect ammonia emission. Mechanistic models are built based on the emission processes. Transport and deposition models are based on the Gaussian dispersion. Measurement methods currently used include chemiluminescence analyzers, denuders, detector tubes, optical absorption techniques, wet chemistry and gas chromatography. Ammonia fluxes are calculated using N balance, micrometeorological, chamber and wind tunnel, and tracer gas methods. Strategies for reducing NH3 losses should be directed towards reducing (1) NH3 formation, (2) NH3 losses immediately after it has been formed, or (3) the NH3 loss potential. Some of the efforts to reduce NH3 emission from animal production facilities include changes in diet, barn design or retrofits to reduce NH3 emissions, cleaning building exhaust air, manure treatment methods, land application techniques, and policies and regulations. Reducing NH3 loss requires a whole farm systems approach, which shows how intervening in one aspect of the farm may affect NH3 losses in other parts of the farm.