Title: Ammonia emissions from cattle-feeding operations. Part 1: issues and emissions. Authors
Submitted to: Scientific and Technical Review
Publication Type: Experiment Station
Publication Acceptance Date: August 15, 2011
Publication Date: December 15, 2012
Citation: Sakirkin, S.L., Cole, N.A., Todd, R.W., Auvermann, B.W. 2012. Ammonia emissions from cattle-feeding operations. Part 1: issues and emissions. Texas Agricultural Experiment Station Bulletin, Air Quality Education in Animal Agriculture, Issues: Ammonia, December, 2011. p. 1-11. Interpretive Summary: Ammonia (NH3) is a lighter-than-air, colorless gas, with a recognizable pungent smell. It is a source of the essential nutrient nitrogen (N) for plants and animals, but is also classified as a hazardous substance by the EPA. Ammonia occurs naturally and occurs in trace amounts in the atmosphere. It is produced by the decomposition of animal and plant matter containing N; including livestock manure. Concentrated animal feeding operations (CAFOs) such as feedyards are a potential source of ammonia. This paper summarizes research concerning ammonia production, concentrations, and emissions at feedyards. The production of ammonia is a complex biological and chemical process, however the primary source at feedyards is urea excreted in urine. Ammonia losses can continue immediately from excretion and as manure is handled, stored, or applied to land as fertilizer. There are varieties of methods to measure atmospheric concentrations of ammonia, each with unique advantages and disadvantages. Atmospheric ammonia concentrations at CAFOs vary greatly, but tend to be greater during daytime than at night. Ammonia concentrations at cattle feedyards rarely exceed 3 ppm. Methods for estimating ammonia emissions from feedyards also vary greatly. North American feedyard studies have observed ammonia emissions from 18 to 104 kg/head annually. Ammonia losses from runoff holding ponds have ranged from 3 to 70% of the N entering the pond and ammonia losses from compost piles have ranged from 10 to 45% of the N entering the compost.
Technical Abstract: Ammonia (NH3) is a lighter-than-air, colorless gas, with a recognizable pungent smell. It is a source of the essential nutrient nitrogen (N) for plants and animals, but it is also classified as a hazardous substance by the EPA. Ammonia occurs naturally and occurs in trace amounts in the atmosphere, where it is the dominant base. Ammonia is produced during the decomposition of animal and plant matter containing N, including livestock manure. There is concern about atmospheric ammonia because of its potential effects on air quality, water quality, and human/animal health. Because it is an essential plant nutrient, N lost to the atmosphere from manure is also a loss of fertilizer value. Ammonia deposition may potentially occur on to sensitive land and water surfaces by dry (normally local) and wet (normally regional) deposition. Concentrated animal feeding operations (CAFOs) import feed ingredients which contain nutrients such as N. Cattle retain a proportion of the N they consume, but 70 to 90% is excreted in feces and urine. Ammonia is produced by breakdown of nitrogenous molecules in the urine and feces, such as urea and protein. Urea in urine is rapidly (i.e within seconds) converted to ammonia and is the major source of ammonia from manure; whereas, the more complex N containing compounds such as proteins are decomposed more slowly by microbes. Ammonia losses from manure can continue as manure is handled, stored, or land-applied as fertilizer. The complexity of biological and chemical processes, coupled with management decisions, complicate the understanding of ammonia emissions from livestock operations. Differences in livestock digestive systems, diets fed, feed and manure management systems, facility design, location, and weather are just a few of the factors that can affect ammonia emissions. Accurate measurement of the atmospheric concentration of ammonia in a large mass of dynamic, open air such as occurs over feedlots is difficult and requires special instrumentation and/or significant labor inputs. There are varieties of methods available to measure atmospheric concentrations of ammonia, each with a unique set of advantages and disadvantages. Atmospheric ammonia concentrations at CAFOs vary considerably, but tend to exhibit a 24-hour pattern, with daytime concentrations greater than nighttime concentrations. Ammonia concentrations at cattle feedyards rarely exceed 3 ppm. Ammonia emissions from CAFO are also difficult to measure because once produced, ammonia is quickly carried away by air currents. Quantifying ammonia flux from the feedyard surface to the atmosphere relies on direct measurement using fast response instrumentation, or on a flux model, which attempts to accurately predict the dispersion of gases through the air. Methods for estimating ammonia emissions from area sources such as feedyards include mass balance, micrometeorology, flux chambers, wind tunnels, and dispersion models. The accuracy and applicability of these estimation methods varies greatly. Few statistical, empirical, and process-based models are currently available to estimate ammonia emissions from CAFOs. Studies conducted at North American feedyards using a variety of measurement methods have observed a wide range of emission rates. Reported emission factors for feedlots have ranged from 18 to 104 kg/head annually, and flux rates have ranged from 3.6 to 88 µg/m2/second. Most studies have also noted seasonal and 24-hour patterns in ammonia flux rates . Reported losses from runoff holding ponds have ranged from 3 to 70% of the N entering the pond and losses from compost windrows have ranged from 10 to 45% of the N entering the compost.