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Various models have been developed to determine ammonia (NH3) emissions from animal manure-processing lagoons to enable relatively simple estimations of emissions. These models allow estimation of actual emissions without intensive field measurements or "one-size-fits-all" emission factors. Two mechanisms for lagoon NH3 emissions exist: (a) diffusive gas exchange from the water surface and (b) mass-flow (bubble transport) from NH3 contained within the ebullition gas bubble (as it rises to the surface) produced from anaerobic decomposition of organic matter. The purpose of this research is to determine whether gas ebullition appreciably affects NH3 emissions and therefore should be considered in emissions models. Specifically, NH3 mass-flow emissions were calculated and compared with calculated diffusive NH3 emissions. Mass-flow NH3 emissions were evaluated based on a two-film model, in connection with the acid dissociation constant of ammonium, to predict the degree of NH3 gas saturation within the bubbles. Average daily ammoniacal nitrogen concentration, pH, and measured biological gas production (ebullition) in conjunction with literature values for Henry's law constant were used to calculate emissions from NH3 saturation of ebullition gases. Ebullition enhancement of NH3 surface emissions due to increased turbulence was estimated from average lagoon ebullition rates and literature values of turbulence enhancement. Ebullition enhancement of NH3 surface emissions and ebullition mass-flow NH3 emissions was determined to be

Swine manure management and storage have been implicated as major sources of increasing agricultural ammonia (NH

Ammonia (NH3 ) has been used as a target gas for nuisance complaints to restrict or close poultry operations near encroaching rural development. There are conflicting data on NH3 emissions from broiler production across the United States. The purpose of this research is to compare emission rates from a Georgia broiler operation across seasons and with other geographical areas in the United States. Comparison of seasonal and geographical emission rates showed large seasonal variation in NH3 emissions for eastern U.S. sites but little seasonal variation in the semi-arid region of the United States. Differences in production management practices, ambient temperature, and animal density did not appear to explain differences in emissions between regions; however, the climatic influence of ambient humidity and litter management practices are thought to be key factors in the generation of emissions.

Measurement of greenhouse gas (GHG) emissions is a challenge to the animal industry as it is difficult to accurately measure enteric emissions from ruminants. Enclosed chambers and tracer-ratio techniques are common measurement approaches, but their use can alter animal diet, behavior and stress levels and soil emission processes. Non-interfering techniques which do not impact soil or air transport processes, or the animal or its surroundings, provide a more appropriate approach to determine absolute emissions. While micrometeorological integrated horizontal flux and mass difference techniques have been used to study animal emissions in paddocks, they require substantial instrumentation and are practical only for small paddocks. Classical micrometeorological methods such as flux-gradient, eddy covariance, relaxed eddy accumulation and boundary layer budgeting have been used to evaluate emissions from larger source areas. This review focuses on a new technique, inverse dispersion analysis, which is a more flexible approach to measure emissions from small paddocks or whole farms as it allows fluxes to be calculated from gas concentration measurements of interest at a point upwind and a point downwind, along with statistical information on wind turbulence measured using a three dimensional sonic anemometer. Our purpose is to discuss advantages and disadvantages of these various techniques to determine absolute amounts of enteric emissions from ruminants, and provide examples of their application. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

Ammonia is the primary basic gas in the atmosphere and has the most important role in the neutralization of atmospheric acids generated by fossil fuel combustion. The reaction product forms a NH(4)(+) aerosol, which is a major component of atmospheric particulates. These NH(4)(+) particulates are part of atmospheric haze and may be transported long distances from the production site before returning to the surface by dry deposition or scavenged by precipitation. Animal production produces a significant component of anthropogenic NH(3) emissions and the National Academy of Sciences concluded that NH(3) emissions estimates from animal feeding operations have not been characterized sufficiently, leading the US Environmental Protection Agency to institute studies in the United States to obtain NH(3) emissions from animal feeding operations under the US Environmental Protection Agency Air Consent Agreement. The objective of this study is to obtain additional broiler NH(3) emissions estimates using a backward Lagrangian stochastic technique. This technique uses NH(3) concentrations measured upwind and downwind of the farm, wind observations, and atmospheric dispersion model calculations to obtain whole-farm emissions. Ammonia emissions were low at bird placement and increased steadily after about the third week of growth. At the end of the flock (47 d, ~297,000 birds), cumulative emissions for the flock cycle period were 0.016 kg of NH(3).bird(-1).flock(-1). Between-flock emissions, including bird harvest, cleanout, temporary storage of litter outside of the buildings, and downtime (buildings closed), added another 0.003 kg of NH(3).bird(-1).flock(-1). Emissions from this broiler farm were less than from some eastern US broiler farms but were comparable to broiler farms in Europe. Based on the results of this study and a similar winter study at this same farm, total flock wintertime and summertime (flock cycle plus between-flock) NH(3) emissions from this farm represented 7.8 and 8.3% of feed N as NH(3)-N, respectively, or an annual average of 8.1%.

SUMMARY Accurately measuring NH3 produced from poultry litter and emitted from mechanically ventilated broiler houses continues to be a challenge. Many technologies and methods are available to measure NH3, with costs ranging from inexpensive (but rather inaccurate, such as colorimetric tubes) to expensive (for precision analytical equipment such as laser spectrometers). This study investigated the variability among selected low, midrange, and high-cost instruments. Inter-instrument and intra-instrument comparisons were made using colorimetric pull tubes and dosimeter tubes, electrochemical sensors, and tunable-diode open-path laser spectrometers (OPL). This study consisted of inside and outside broiler house studies to evaluate instrument performance under different environmental conditions and NH3 concentrations. The OPL showed the least variation during the in-house and outside comparisons. The electrochemical sensors and colorimetric tubes performed well at NH3 levels typically found in a properly ventilated broiler house. With no ventilation, variation among instruments increased as NH3 concentrations increased. With the exception of the OPL, concentrations on the outside were too low and environmental elements were too harsh for these instruments to perform well.

SUMMARY Within broiler production facilities, NH3 concentrations have always been of concern from a bird performance and worker health standpoint. However, NH3 emitted from poultry houses is receiving increased attention from the environmental and community nuisance perspectives. Studies on NH3 emissions from poultry operations found within the literature do not address how NH3 disperses or the actual concentrations observed at varying distances downwind from poultry houses. The objective of this study was to measure downwind NH3 concentrations emitted from broiler houses when ventilation rates would be at a maximum. Open-path laser spectrometers were utilized for this study and for period 1 were placed 100, 200, and 300 ft from the houses from 28 to 49 d and in period 2 were placed at 100, 200, and 500 ft from 50 to 56 d. Data were collected during the last 4 wk of a 56-d grow-out cycle in 2 periods during a summer flock on a 4-house broiler farm located in northeastern Georgia. Ammonia concentrations were lower as distance from the houses increased, with NH3 levels at 100, 200, 300, and 500 ft being less than 1 ppm in approximately 60, 75, 85, and 90% of the observations, respectively. Ammonia concentrations extending to 100 ft from the houses were influenced by the tunnel fans themselves. Wind direction and wind speed were the factors that significantly influenced downstream NH3 concentrations beyond 100 ft. At no time did measured NH3 levels meet or exceed established Occupational Safety and Health Administration-US Environmental Protection Agency NH3 odor-detection threshold values during this study.

Inverse-dispersion calculations can be used to infer atmospheric emission rates through a combination of downwind gas concentrations and dispersion model predictions. With multiple concentration sensors downwind of a compound source (whose component positions are known) it is possible to calculate the component emissions. With this in mind, a field experiment was conducted to examine the feasibility of such multi-source inferences, using four synthetic area sources and eight concentration sensors arranged in different configurations. Multi-source problems tend to be mathematically ill-conditioned, as expressed by the condition number κ. In our most successful configuration (average κ = 4.2) the total emissions from all sources were deduced to within 10% on average, while component emissions were deduced to within 50%. In our least successful configuration (average κ = 91) the total emissions were calculated to within only 50%, and component calculations were highly inaccurate. Our study indicates that the most accurate multi-source inferences will occur if each sensor is influenced by only a single source. A “progressive” layout is the next best: one sensor is positioned to “see” only one source, the next sensor is placed to see the first source and another, a third sensor is placed to see the previous two plus a third, and so on. When it is not possible to isolate any sources κ is large and the accuracy of a multi-source inference is doubtful.

Concentrated animal feeding operations (CAFOs) are major sources of ammonia emitted into the atmosphere. There is considerable literature on ammonia emissions from poultry and swine CAFO, but few comprehensive studies have investigated large, open lot beef cattle feedyards. Ammonia emission rates and emission factors for a 77-ha, 45 000-head commercial beef cattle feedyard on the southern High Plains were quantified using measured profiles of ammonia concentration, wind speed and air temperature, and an inverse dispersion model. Mean summer emission rate was 7420 kg NH 3 d −1 , and winter emission rate was about half that, at 3330 kg NH 3 d −1 . Annual NH 3 –N emission rate was 4430 kg NH 3 –N d −1 , which was 53% of the N fed to cattle. Daily per capita NH 3 –N losses increased by 10–64% after the daily per capita N in feed rations increased by 15–26%. Annual emission factors for the pen area of the feedyard were 19.3 kg NH 3 (head fed) −1 , or 70.2 kg NH 3 Mg −1 biomass produced. Annual emission factors for the retention pond of the feedyard were estimated to be 0.9 kg NH 3 (head fed) −1 , or 3.2 kg NH 3 Mg −1 biomass produced.

We use an inverse–dispersion technique to diagnose gas emissions (ammonia) from a swine farm. A backward Lagrangian stochastic (bLS) model gives the emission-concentration relationship, so that downwind gas concentration establishes emissions. The bLS model takes as input the average wind velocity and direction, surface roughness, and atmospheric stability. Despite ignoring windcomplexity andassuming a simplifiedsource configuration in the mod el calculations, we argue that with concentration andwindmeasuredsufficiently far from the farm the errors can be relatively small. An important part of our analysis was identifying periods likely to give erroneous results. The resulting emission calculations (6.5 and16 g animal � 1 day � 1 in March andJuly, respectively) are plausible in the light of

Inverse-dispersion techniques allow inference of a gas emission rate Q from measured air concentration. In “ideal surface layer problems,” where Monin–Obukhov similarity theory (MOST) describes the winds transporting the gas, the application of the technique can be straightforward. This study examines the accuracy of an ideal MOST-based inference, but in a nonideal setting. From a 6 m × 6 m synthetic area source surrounded by a 20 m × 20 m square border of a windbreak fence (1.25 m tall), Q is estimated. Open-path lasers gave line-averaged concentration CL at positions downwind of the source, and an idealized backward Lagrangian stochastic (bLS) dispersion model was used to infer QbLS. Despite the disturbance of the mean wind and turbulence caused by the fence, the QbLS estimates were accurate when ambient winds (measured upwind of the plot) were assumed in the bLS model. In the worst cases, with CL measured adjacent to a plot fence, QbLS overestimated Q by an average of 50%. However, if these near-fence locations are eliminated, QbLS averaged within 2% of the true Q over 61 fifteen-minute observations (with a standard deviation σQ/Q = 0.20). Poorer accuracy occurred when in-plot wind measurements were used in the bLS model. The results show that when an inverse-dispersion technique is applied to disturbed flows without accounting for the disturbance, the outcome may still be of acceptable accuracy if judgment is applied in the placement of the concentration detector.

T he topic of global change is found almost daily in newspaper and magazine articles and on television. Global change refers to large-scale changes in the Earth's biological, geological, hydrological, and atmospheric systems, whether of human or natural origin. The primary concern of global change has centered on the rapid increase in atmospheric concentrations of primary greenhouse gases (carbon dioxide [CO2], methane [CH4], and nitrous oxide [N20]) since the Industrial Revolution in the latter part of the 19th century.1 Increased concentrations of all 3 of these gases trap more of the sun's energy close to Earth's surface and lead to global warming, hence the reason that these gases are often referred to as "greenhouse gases." The concentration of CO2 has increased by about 35% compared to preindustrial times and is predicted to reach twice the preindustrial concentration within the 21st century.2 Plants convert CO2 in the air into plant tissue, so CO2 enrichment generally stimulates plant growth and improves the efficiency with which plants use water.3 These changes, in turn, influence plant nutrition and the cycling of carbon and other mineral elements through the soil/plant system4 and may have long-lasting ecological consequences for rangelands and pasturelands. For example, increased plant production with CO2 enrichment5'6 requires additional soil nitrogen, which is limiting in most rangeland and pastureland ecosystems, and this will modify nutrient cycling because less nitrogen is available for soil microorganisms to decompose plant materials. The increase in methane and nitrous oxide concentrations in the atmosphere that have occurred are also a cause for concern as their warming potential as greenhouse gases surpasses that of CO 2.' Global warming is predicted to have numerous impacts on our climate, including altered precipitation patterns and a potential rise in sea levels. As such, global warming may have profound impacts on human activities and enterprises and is thus a concern to many. Rangelands and pasturelands provide much of the world's food and fiber, and because they occupy an extensive land area, changes in how these lands function could increase or reduce the atmospheric load of greenhouse gases. For example, land management strategies that increase the storage of carbon in plant biomass and/or soil organic matter on rangelands and pasturelands, in a process termed "carbon sequestration," offer opportunities to mitigate the rise in atmospheric CO2 concentrations.8 To evaluate potential impacts that increasing concentrations of greenhouse gases may have, the United States Department of Agriculture-Agricultural Research Service (USDA-ARS), in its Natural Resources and Sustainable Agricultural Systems program, established a Global Change

In trials of a mass balance method for measuring methane (CH 4 ) emissions, sonic anemometers and an open-path laser were used to measure the transport of CH 4 released from a ground-level source across a downwind face 50 m long and 6 m high. Release rates matched emissions expected from dairy herds of 2 to 40 cows. The long laser path permitted inferences from measurements in only two planes, one upwind and one downwind, while the fast-response instruments allowed calculation of instantaneous horizontal fluxes rather than fluxes calculated from mean wind speeds and mean concentrations. The detection limit of the lasers was 0.02 ppmv, with the separation between the transmitters and reflectors being about 50 m. The main conclusions from the 23 trials were: (1) Emissions calculated from mean wind speeds and concentrations overestimated the true emissions calculated from instantaneous measurements by 5%. (2) Because of small changes in methane concentration, the minimum sample size in animal trials would be 10 dairy cows, producing about 40 mg CH 4 s −1 . (3) For release rates greater than 40 mg CH 4 s −1 and with sufficient replication, the technique could detect a change in production rate of 9% ( P = 0.05 ). (4) Attention to perceived weaknesses in the present technique should help towards detecting changes of 5%.

Concentrated animal production may represent a significant source for ammonia emissions to the environment. Most concentrated animal production systems use anaerobic or liquid/slurry systems for wasteholding; thus, it is desirable to be able to predict ammonia emissions from these systems. A process model was developed to use commonly available measurements, including effluent concentration, water temperature, wind speed, and effluent pH. The developed model simulated emissions, as measured by micrometeorological techniques, with an accuracy that explains 70% of the variability of the data using average daily emissions and explains 50% of the variability of the data using 4-h average data. The process model did not show increased accuracy over a statistical model, but the deviations between model and measurement were distributed more evenly in the case of the process model than in the case of the statistical model.

This paper examines the accuracy with which trace gas fluxes, from a source that disturbs the local wind and microclimate, may be estimated from measured concentrations, above or downwind from the source. The familiar flux‐gradient methods, even if carefully applied within the near-surface constant-flux-layer, nevertheless posit horizontally-uniform wind and stability. Errors result if the windflow is actually advective (i.e. disturbed), so that its state is evolving in the alongwind direction. We take as an illustration the case of a gas evaporating uniformly .Q; kg m 2 s 1 / from a small lagoon. We modify the Rao‐Wyngaard‐Cote local advection model, verify it against existing observations of disturbed flows, then calculate the fields of windspeed, temperature and tracer concentration over land and lake. From these “data” we calculate several estimates of the (known) source strength Q. Results by integration of the horizontal flux .Q IHF / prove the most satisfactory, followed by those using a source‐receptor relationship based on a backward Lagrangian stochastic method .Q bLS /. Flux‐gradient estimates Q FG can be very seriously in error, and should only be used with caution in disturbed flow. These findings have generality beyond the specific case of a lagoon flow. © 2001 Published by Elsevier Science B.V.

The paper examines the strengths and weaknesses of a rangeof meteorological flux measurement techniques that mightbe used to verify predictions of greenhouse gas inventories.Recent research into emissions of methane (CH4)produced by enteric fermentation in grazing cattle and sheepis used to illustrate various methodologies. Quantifying thisimportant source presents special difficulties because the animalsconstitute moving, heterogeneously distributed, intermittent, pointsources. There are two general approaches: one, from the bottom up,involves direct measurements of emissions from a known number ofanimals, and the other, from the top down, infers areal emissions ofCH4 from its atmospheric signature. A mass-balance methodproved successful for bottom-up verification. It permits undisturbedgrazing, has a simple theoretical basis and is appropriate for fluxmeasurements on small plots and where there are scattered pointsources. The top-down methodologies include conventional flux-gradientapproaches and convective and nocturnal boundary-layer (CBL and NBL)budgeting schemes. Particular attention is given to CBL budget methods inboth differential and integral form. All top-down methodologies require ideal weather conditions for their application, and they suffer from the scattered nature of the source, varying wind directions and low instrument resolution. As for mass-balance, flux-gradient micrometeorological measurements were in good agreement with inventory predictions of CH4 production by livestock, but the standard errors associated with both methods were too large to permit detection of changes of a few per cent in emission rate, which might be important for inventory, regulatory or research purposes. Fluxes calculated by CBL and NBL methods were of the same order of magnitude as inventory predictions, but more improvement is needed before their use can be endorsed. Opportunities for improving the precision of both bottom-up and top-down methodologies are discussed.

Gaseous methane (CH4) emissions from a swine waste holding lagoon were determined periodically during the year. Micrometeorological techniques were used in order that emission rates from the lagoon were measured under ambient conditions with little disturbance to the natural environment. During the cold winter measurement period, CH4 fluxes were linearly related to lagoon water temperature below 22°C (r=0.87). During warmer measurement periods, both water and air temperatures and windspeed affected emissions rates. In general, flux rates followed a diurnal pattern with greater fluxes during the day when both temperature and windspeed were greatest. Mathematical models using air and water temperature and windspeed factors could explain 47 to 75% of the variation in fluxes. Daily emission rates ranged from 1 to 500 kg CH4 ha−1 d−1. The average flux for the year was 52.3 kg CH4 ha−1 d−1 which corresponded to about 5.6 kg CH4 animal−1 yr−1 from the primary lagoon.

A mass balance method is described for calculating gas production from a surface or volume source in a small test plot from measurements of differences in the horizontal fluxes of the gas across upwind and downwind boundaries. It employs a square plot, 24 m×24 m, with measurements of gas concentration at four heights (up to 3.5 m) along each of the four boundaries. Gas concentrations are multiplied by the appropriate vector winds to yield the horizontal fluxes at each height on each boundary. The difference between these fluxes integrated over downwind and upwind boundaries represents production. Illustrations of the method, which involve exchanges of methane and carbon dioxide, are drawn from experiments with landfills, pastures and grazing animals. Tests included calculation of recovery rates from known gas releases and comparisons with a conventional micrometeorological approach and a backward dispersion model. The method performed satisfactorily in all cases. Its sensitivity for measuring exchanges of CO2, CH4 and N2O in various scenarios was examined. As employed by us, the mass balance method can suffer from errors arising from the large number of gas analyses required for a flux determination, and becomes unreliable when there are light winds and variable wind directions. On the other hand, it is non-disturbing, has a simple theoretical basis, is independent of atmospheric stability or the shape of the wind profile, and is appropriate for flux measurement in situations where conventional micrometeorological methods can not be used, e.g. for small plots, elevated point sources, and heterogeneous surface sources.

Isotopes of nitrogen (15N) have been used to evaluate N transport in soil–plant systems, but these studies generally ignore the atmospheric component of N balance. Recent studies of atmospheric ammonia (NH3) transport have shown the gaseous N component can be significant due to emission and absorption exchanges with the atmosphere. The purpose of this paper is to review measurements of atmospheric N cycling made by ourselves and others, and investigate how atmospheric transport may influence the conclusions of isotopic N studies. Soil and plant N transport were studied using 15N while simultaneously measuring net atmospheric NH3 transport using micrometeorological techniques. Simultaneous 15N and micrometeorological studies have shown significant gaseous NH3 losses from soils and plants as well as the potential for significant NH3 absorption. These measurements have shown N transport measured by the two techniques to agree closely when there was no plant activity (during drought). With plant activity, and the associated substitution of 15N in the plant by 14N from atmospheric NH3, NH3 losses measured by 15N were 2 to 6 times larger than net NH3 losses measured by micrometeorological techniques. Although 15N studies are valuable for comparison of treatments, caution must be exercised in the use of isotopes where isotope exchange between the plant and atmosphere has not been taken into consideration.

Ammonia gas is the only significant basic gas that neutralizes atmospheric acid gases produced from combustion of fossil fuels. This reaction produces an aerosol that is a component of atmospheric haze, is implicated in nitrogen (N) deposition, and may be a potential human health hazard. Because of the potential impact of NH3 emissions, environmentally and economically, the objective of this study was to obtain representative and accurate NH3 emissions data from large dairy farms (>800 cows) in Wisconsin. Ammonia concentrations and climatic measurements were made on 3 dairy farms during winter, summer, and autumn to calculate emissions using an inverse-dispersion analysis technique. These study farms were confinement systems utilizing freestall housing with nearby sand separators and lagoons for waste management. Emissions were calculated from the whole farm including the barns and any waste management components (lagoons and sand separators), and from these components alone when possible. During winter, the lagoons' NH3 emissions were very low and not measurable. During autumn and summer, whole-farm emissions were significantly larger than during winter, with about two-thirds of the total emissions originating from the waste management systems. The mean whole-farm NH3 emissions in winter, autumn, and summer were 1.5, 7.5, and 13.7% of feed N inputs emitted as NH3-N, respectively. Average annual emission comparisons on a unit basis between the 3 farms were similar at 7.0, 7.5, and 8.4% of input feed N emitted as NH3-N, with an annual average for all 3 farms of 7.6 +/- 1.5%. These winter, summer, autumn, and average annual NH3 emissions are considerably smaller than currently used estimates for dairy farms, and smaller than emissions from other types of animal-feeding operations.

Trace-gas emissions from animal feeding operations (AFOs) can contribute to air quality and global change gases. Previous and current estimated gas emissions from AFOs vary widely and many do not consider all forms of carbon (C) and nitrogen (N) emissions. Studies have found that as methanogenesis in the lagoons increased, conversion of ammonium (NH4 +) to dinitrogen (N2) also increased. The purpose of this research was to measure N2 and CH4 emissions from swine AFOs in three locations of the U.S. and to evaluate the possible universal relationship between lagoon methanogenesis and the conversion of NH4 + to N2 gas. This relationship was tested by measuring N2 and CH4 emissions in two climates at 22 different farms. Methanogenesis was correlated with NH4 +-to-N2 conversion by a near-constant N2 to CH4 emissions ratio of 0.20, regardless of C loading and climatic effects. The process is shown to be thermodynamically favored when there is competition between NH4 + oxidizing reactions. Under methanogenic conditions (redox potentials of methanogenesis) N2 production is favorable and nitrification/denitrification is not. Thus, N2 production is stimulated in methanogenic conditions. Evaluation of NH3 gas emissions from AFOs must consider other N emissions than NH3. Finally, a statistical model was developed to estimate methane and N2 emissions (kg gas ha−1) given feed input per lagoon surface area (kg feed ha−1) and local air temperature. Further studies are needed to investigate the mechanisms involved in manure processing and isolate the favorable mechanisms into engineering improved manure processing.