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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.

Methane (CH 4 ) and ammonia (NH 3 ) are emitted to the atmosphere during anaerobic processing of organic matter, and both gases have detrimental environmental effects. Methane conversion to biofuel production has been suggested to reduce CH 4 emissions from animal manure processing systems. The purpose of this research is to evaluate the change in CH 4 and NH 3 emissions in an animal feeding operation due to biofuel production from the animal manure. Gas emissions were measured from swine farms differing only in their manure-management treatment systems (conventional vs. biofuel). By removing organic matter (i.e., carbon) from the biofuel farms' manure-processing lagoons, average annual CH 4 emissions were decreased by 47% compared with the conventional farm. This represents a net 44% decrease in global warming potential (CO 2 equivalent) by gases emitted from the biofuel farms compared with conventional farms. However, because of the reduction of methanogenesis and its reduced effect on the chemical conversion of ammonium (NH 4 + ) to dinitrogen (N 2 ) gas, NH 3 emissions in the biofuel farms increased by 46% over the conventional farms. These studies show that what is considered an environmentally friendly technology had mixed results and that all components of a system should be studied when making changes to existing systems.

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.

Ammonia (NH3) emissions were determined from three commercial dairy farms in the north-central U.S. The dairies employed similar management, having naturally ventilated free-stall barns where barn waste is scraped and transferred to outdoor lagoons. Three potential emission sources were distinguished at each farm: barns, lagoons, and sand separators. A backward Lagrangian stochastic (bLS) inverse-dispersion technique was used to measure emissions. Total farm emission varied from 15 to 330 kg NH3 d-1 depending on the farm and season. Inter-farm variability was largely explained by farm size (animal population). Emissions showed variability on seasonal and daily scales: summer rates were roughly ten times those of the winter, and mid-day rates were approximately three times those at night. The lagoons emitted 37% to 63% of the farm total during summer and fall, but they were frozen in winter and their emissions were immeasurably small. The yearly per-animal emissions from the three dairies were estimated at 20, 19, and 20 kg NH3 animal-1 year-1. Regarding the measurement technique, bLS proved well-suited to our study. With modest resources we were able to measure emissions from the variety of sources at each farm and quickly move between farms. Overall agreement in measured emissions at the three farms, together with a general harmony of our measurements with those from previous studies, provides a measure of confidence in the measurement strategy.

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.

An inverse-dispersion technique is used to calculate ammonia (NH3) gas emissions from a cattle feedlot. The technique relies on a simple backward Lagrangian stochastic (bLS) dispersion model to relate atmospheric NH3 concentration to the emission rate QbLS. Because the wind and the source configuration are complicated, the optimal implementation of the technique is unclear. Two categorically different measurement locations (for concentration and winds) are considered: within the feedlot and downwind. The in-feedlot location proved superior, giving a nearly continuous QbLS timeseries. We found average emissions of 0.15 kg NH3 animal � 1 day � 1 in both 2004 and 2005, representing a loss of 63% (2004) or 65% (2005) of the dietary nitrogen in the animal feed. Downwind measurement locations were less useful for several reasons: a narrow range of useable wind directions; ambiguity in the choice of wind statistics to use in the calculations; low NH3 concentrations; and downwind deposition of NH3. When addressing a large source (like a feedlot) that modifies the ambient wind flow, we recommend in-source measurements for use in inverse-dispersion applications. # 2007 Elsevier B.V. All rights reserved.

Estimates of enteric methane (CH4) emissions from ruminants are typically measured by confining animals in large chambers, using head hoods or masks, or by a ratiometric technique involving sampling respired air of the animal. These techniques are not appropriate to evaluate large-scale farm emissions and the variability between farms that may be partly attributed to different farm management. This study describes the application of an inverse-dispersion technique to calculate farm emissions in a controlled tracer-release experiment. Our study was conducted at a commercial dairy farm in southern Alberta, Canada (total of 321 cattle, including 152 lactating dairy cows). Sulfur hexafluoride (SF6) and CH4 were released from 10 outlet locations (barn and open pens) using mass-flow controllers. A Lagrangian stochastic (LS) dispersion model was then used to infer farm emissions from downwind gas concentrations. Concentrations of SF6 and CH4 were measured by gas chromatography analysis and open path lasers, respectively. Wind statistics were measured with a three-dimensional sonic anemometer. Comparing the inferred emissions with the known release rate showed we recovered 86% of the released CH4 and 100% of the released SF6. The location of the concentration observations downwind of the farm was critically important to the success of this technique.

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%.

The gas emission rate Q from an artificial 36-m2 surface area source was inferred from line-average concentration CL measured by an open-path laser situated up to 100 m downwind. Using a backward Lagrangian stochastic (bLS) model, a theoretical CL/Q relationship was established for each experimental trial by simulating an ensemble of fluid-element paths arriving in the laser beam under the prevailing micrometeorological conditions. The diagnosed emission rates (QbLS) were satisfactory for trials done when Monin‐Obukhov similarity theory gave a good description of the surface layer, but were poor during periods of extreme atmospheric stability ( | L | # 2 m) and transition periods in stratification. With such periods eliminated, the average value of the 15-min ratios QbLS/Q over n 5 77 fifteen-minute trials spanning 6 days was 1.02. Individual 15-min estimates, however, exhibited sizable variability about the true rate, with the standard deviation in QbLS/Q being sQ/Q 5 0.36. This variability is lessened (sQ/Q 5 0.22, n 5 46) if one excludes cases in which the detecting laser path lay above or immediately downwind from the source—a circumstance in which the laser path lies at the edge of the gas plume.

Ammonia (NH3) from confined animal feeding operations is emitted from several sources including lagoons, field applications, and houses. This paper presents studies that were conducted to evaluate NH3 emissions from swine finisher and sow animal houses in the southeastern USA. Management and climate variables including animal weight, feed consumption, housing gutter water temperature, total time fans operated per day, house air temperature, house ambient NH3 concentration, and animal numbers were measured to determine their individual and combined effect on NH3 emissions. Ammonia emissions varied on daily and seasonal bases with higher emissions during warmer periods. For finishers, the summertime housing emissions on a per-animal basis were 2.4 times higher than wintertime (7.0 vs. 3.3 g NH3 animal(-1) d(-1)) or 3.2 times higher when compared on an animal unit (AU) basis (1 AU = 500 kg) because of climate and animal size differences between measurement periods. For summertime, the emission factor for the finishing pigs was 7.8 times higher than for sows on an animal basis and 25.6 times higher on an AU basis. Simple models were developed for housing emissions based on (i) all measured factors that were independent of each other and (ii) on three commonly measured management factors. The two models explained 97 and 64%, respectively, of variations in emissions. Ammonia emissions were found to be somewhat less than other studies on the same type housing due to more representative housing concentration measurements and calibration of exhaust fans; thus, emission factors for these type houses will be less than previously thought.

Concentrated animal production can have a significant effect on the atomospheric environment. Methane (CH4) emissions from two swine waste holding lagoons were determined periodically in 1997 and 1998. Emission rates from the lagoons were measured under ambient conditions with little disturbance to the natural environment. One farm (NC10) used a periodic ‘flush’ to remove wastes (8 h cycle). The second farm (NC20) used a ‘pull-plug’ system with a 1 week cycle time. In general, flux rates followed a diurnal pattern with greater fluxes during the day when both temperature and windspeed were greatest. Methane emissions from the lagoons were related to windspeed, effluent temperature and volatile solid loading into the system. Average emissions from NC10 ranged from 20 to 115 kg CH4 ha−1 per day. Greatest emissions were during the spring period when the sludge depth was deepest. Emissions from NC20 were much less (5.3–10.7 kg CH4 ha−1 per day) due primarily to fewer number of animals and type of manure handling system. Emissions followed a diurnal pattern with greatest emissions during the day when effluent temperature was greatest. The average flux for the year from the two lagoons were 62 and 8 kg CH4 ha−1 per day which corresponded to 6.0 and 1.6 kg CH4 per animal per year, respectively.

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.

method of application, climatic conditions, and chemical and physical soil properties (Misselbrook et al., 1996; In the United States, swine (Sus scrofa ) operations produce more Lowrance et al., 1998). As much as 13% of applied NH4 than 14 Tg of manure each year. About 30% of this manure is stored in anaerobic lagoons before application to land. While land application can be volatilized during irrigation before the effluent of manure supplies nutrients for crop production, it may lead to reaches the soil, with an additional 10 to 70% lost within gaseous emissions of ammonia (NH3 ) and nitrous oxide (N2O). Our 48 h after irrigation (Sharpe and Harper, 1997; Schilkeobjectives were to quantify gaseous fluxes of NH3 and N2O from Gartley and Sims, 1993). Large losses of NH3 can result effluent applications under field conditions. Three applications of in insufficient N availability for plant uptake or environswine effluent were applied to soybean [Glycine max (L.) Merr. mental degradation. Ammonia is the primary neutraliz‘Brim’] and gaseous fluxes were determined from gas concentration ing agent for acid gases in the atmosphere and is a profiles and the flux-gradient gas transport technique. About 12% of common component of atmospheric aerosols. Volatilammonium (NH4–N) in the effluent was lost through drift or secondary ization of NH3 may result in eutrophication of natural volatilization of NH3 during irrigation. An additional 23% was volatilecosystems. Natural ecosystems are thought to be net ized within 48 h of application. Under conditions of low windspeed

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.

An inverse Lagrangian dispersion analysis was used to infer sources and sinks of ammonia (NH 3 ) in the canopy of a dense corn crop (LAI∼5) subject to frequent sprinkler irrigation with dairy effluent. Source strengths were calculated for four canopy layers using statistics of the canopy turbulence and measurements of atmospheric NH 3 concentrations at six heights within the canopy and two above it. The analysis was performed for 4 days of measurement, two immediately following and two several days after effluent application. The analysis provided estimates of the net loss of NH 3 from the canopy, which agreed well (within 20%) with conventional aerodynamic estimates of the flux of NH 3 in the crop boundary layer. In addition, it permitted an examination of processes of loss within the canopy. Small, but not insignificant NH 3 losses were inferred for the soil. These ranged from 4% of the total loss several days after effluent application to 30% on the day of application. Unexpectedly large losses occurred from the foliage in the top half of the canopy. Calculations of apparent ammonia compensation points for the corn leaves indicated that even days after the surface water had evaporated, compensation points were too high for the loss to be explained by diffusion through stomata. It was surmised that the loss was from residues remaining on foliage surfaces. Volatilization losses from the developed crop were estimated to be about 30% of the N applied, 18% coming from soil and foliage and 12% from spray losses during effluent application.

Seventy-five percent of swine (Sus scrofa) production systems in North America use anaerobic or liquid-slurry systems for waste holding or disposal. Accurate emissions data and emission factors are needed for engineering, planning, and regulatory agencies. These data are used for system design and evaluation of the effect of animal concentrations on the regional soil, surface and ground waters, and atmospheric environments. Noninvasive techniques were used to evaluate trace gases without disturbing the meteorology or lagoon system being measured. Micrometeorological and gas sensors were mounted on a submersible barge in the center of the lagoon for use with flux-gradient methodology to determine trace gas fluxes, without disturbing atmospheric transport processes, over extended periods. Collateral measurements included lagoon nutrient, dissolved gas concentrations, and sludge gas mass flux. Ammonia emissions varied diurnally and seasonally and were highly correlated with windspeed and water temperature. Nutrient loading measurements showed that mobile ions, which were nonvolatile, were constant throughout four successive lagoons. Immobile ions concentrated primarily in the sludge layer of the first lagoon. Measurements of denitrification N 2 losses suggest as much N 2 -N lost as from NH 3 -N. Ammonia gas emissions are not as large a percentage of total nitrogen input to the lagoons as previously thought but unaccounted-for nitrogen requires further research.

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.

In the USA, swine operations produce more than 14 Tg of manure each year. About 30% of this manure is stored in anaerobic lagoons before effluent applications to land. Although land application is the preferred means of disposal and can supply nutrients for crop production, it leads to gaseous emissions of ammonia (NH 3 ) and nitrous oxide (N 2 O), both of which can be detrimental to the environment. Our objectives were to quantify gaseous emissions of NH 3 and N 2 O from effluent applications under field conditions and to relate N 2 O fluxes to soil water content. Three applications of swine effluent were applied to oat (A vena sativa GA-Mitchell) starting at heading stage. Gaseous fluxes were determined from gas concentration profiles and the momentum balance transport coefficient. About 13% of the ammonium (NH 4 -N) was lost through drift or volatilization of NH 3 during irrigation. An additional 69% was volatilized within 24 h of application. Nitrous oxide emissions were low before effluent applications (19 mg N 2 O-N ha -1 d -1 ) and increased to 0.25 to 0.38 kg N 2 O-N ha -1 d -1 after irrigation. Total N 2 O emissions during the measurement period were 4.7 kg N 2 O-N ha -1 , which was about 13% of total N applied. The large losses of NH, and N 2 O illustrate the difficulty of basing emuent irrigation schedules on N concentrations and the data indicate that compared to N 2 O, NH 3 emissions made greater contributions to N enrichment of the environment.

Isotopic 15 N tracers have been important tools in the understanding of N cycling in agricultural and natural soil-plant systems. The objectives of this research were to quantify losses of 15 N under controlled conditions, evaluate 15 NH 3 transport between plants, and assess the potential for error associated with the use of N isotopes. Corn (Zea mays L.) was grown hydroponically in 5- to 15-mm-diam. gravel in twelve 162-L barrels. All N was applied as NO 3 with enrichment periods of full season, planting through anthesis, anthesis to harvest, or no 15 N applied. Plant growth and total N accumulation followed normal growth curves and maximum N content was obtained at anthesis. When 15 N treatments stopped at anthesis, plants lost 15 N (presumably as 15 NH 3 ) equivalent to about 23% of total plant N between anthesis and harvest. In treatments in which 15 N applications started at anthesis, total N content in the leaves and stems decreased between anthesis and harvest while 15 N content increased indicating a substitution of recently absorbed N for N compounds translocated to the fruit. Volatile losses of N indicate that caution must be exercised when conducting and interpreting 15 N experiments. Significant plant-to-plant transport of 15 NH 3 showed that decreases in plant 15 N content could not be used to estimate NH 3 volatilization for an entire field.

An understanding of N cycling in agricultural systems is necessary to optimize N-use efficiency and reduce N losses to the environment. The objectives of this research were to evaluate N cycling in a highly fertilized grassland in a humid temperate climate and to observe the effects of N surplus and deficit on NH3 absorption-desorption by the grass. Soil, plant, and weather measurements were taken concurrently and soil-plant-atmosphere N transport were determined. After N application, soil inorganic N decreased rapidly to background levels, due to possible microbial immobilization and plant N demand. Much of the immobilized N was remobilized during the growth period, but at insufficient rates to avoid N stress by the crop, as shown by absorption of NH3. During spring, 45% of the plant N was derived from applied fertilizer, with the balance obtained from mineralized organic N (49%) and absorption of NH3 (6%). During summer, fertilizer N accounted for 60% of accumulated grass N and NH3 absorption accounted for 11% of N not derived from fertilizer (4% of the total N), with the balance coming from mineralized organic N. Soil water content and wind speed were the dominant factors influencing the crop NH3 compensation point (CP). The daily NH3 CP was variable, but the average seasonal NH3 CP was about 14 μg m -3 .

Ammonia emission into the atmosphere is of concern because of its potential impact on atmospheric aerosol chemistry and fertilizer N use efficiency. The purpose of this study was to evaluate the effects of N surplus and deficit on soil-plant-atmosphere NH3 exchange in a temperate humid grassland. Plant and soil N measurements were made along with NH 3 fluxes using flux-gradient techniques. Ammonia flux was related to the plant ammonia compensation point (NH 3 CP), which was controlled by plant N concentration and management practices (such as harvest and fertilization). The measured fluxes were generally much larger during daytime than during nighttime. The daily variation in flux was apparently caused by higher diffusive resistance at night. Generally, there were no significant differences between daytime and nighttime NH 3 CP. Ammonia was absorbed in dew and released during dew evaporation; however, nighttime absorption exceeded daytime release, with some of the N apparently being captured by the crop.

Ammonia transport in cropping systems can affect atmospheric pollution, soil-plant N relationships, and crop N-use efficiency. The purpose of this study was to evaluate the N dynamics of a corn (Zea mays L., Pioneer hybrid 3379) cropping system and determine the effect of NH 3 transport and crop NH 3 compensation point on N relations in the crop. Soil and plant N measurements were made during the growing season along with plant-atmosphere NH 3 transport using flux-gradient micrometeorological techniques. The crop generally emitted NH 3 throughout the season when the atmospheric NH 3 concentrations were near background levels. During periods of high atmospheric NH 3 concentrations, the crop absorbed significant amounts of NH 3 from the atmosphere. Net seasonal NH 3 transport was determined to be a small loss, based on the number of measurement periods throughout the growing season; however, N isotope studies in a nearby field estimated significant NH 3 losses. Nitrogen isotope studies cannot account for the substitution of 14 NH 3 absorbed from the atmosphere for volatilized 15 NH 3 . These results indicate that care must be taken when using N isotopes to evaluate N losses from cropping systems when plants are actively growing. Nitrous oxide flux was measured late in the cropping season, but showed small denitrification losses during the measurement period. The crop NH 3 compensation point varied during the time of day and with respect to soil-plant-atmosphere influence. Net NH 3 transport accounted for little of the N lost from this cropping system.

Methane (CH) and ammonia (NH) are emitted from swine-manure processing lagoons, contributing to global climate change and reducing air quality. Manure diverted to biofuel production is proposed as a means to reduce CH emissions. At a swine confined animal feeding operation in the U.S. Central Great Basin, animal manure was diverted from 12 farms to a biofuel facility and converted to methanol. Ammonia emissions were determined using the De Visscher Model from measured data of dissolved lagoon ammoniacal N concentrations, pH, temperature, and wind speed at the lagoon sites. Other lagoon gas emissions were measured with subsurface gas collection devices and gas chromatography analysis. During 2 yr of study, CO and CH emissions from the primary lagoons decreased 11 and 12%, respectfully, as a result of the biofuel process, compared with concurrently measured control lagoon emissions. Ammonia emissions increased 47% compared with control lagoons. The reduction of CH and increase in NH emissions agrees with a short-term study measured at this location by Lagrangian inverse dispersion analysis. The increase in NH emissions was primarily due to an increase in lagoon solution pH attributable to decreased methanogenesis. Also observed due to biofuel production was a 20% decrease in conversion of total ammoniacal N to N, a secondary process for the removal of N in anaerobic waste lagoons. The increase in NH emissions can be partially attributed to the decrease in N production by a proposed NH conversion to N mechanism. This mechanism predicts that a decrease in NH conversion to N increases ammoniacal N pH. Both effects increase NH emissions. It is unknown whether the decrease in NH conversion to N is a direct or physical result of the decrease in methanogenesis. Procedures and practices intended to reduce emissions of one pollutant can have an unintended consequence on the emissions of another pollutant.

This paper compares gas emissions from mechanically-ventilated houses as measured by two techniques: air mass-balance and inverse-dispersion analysis. Ammonia emissions were measured concurrently from a poultry farm during a 45-day flock cycle. Total flock emissions calculated by the inverse-dispersion technique was 75% of that determined by the air mass-balance measurements. The difference was not uniform over the flock cycle, with good agreement during the first 28 days (2%), but poorer thereafter (35%). The divergence between the two techniques corresponded to an increase in the house ventilation rate.

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.

Air emissions from animal feeding operations have become a growing concern for producers and their neighbors. Much work has been done to quantify emission rates; however, little information has been provided about air quality downwind from these facilities. This study investigates ammonia and PM2.5 (particulate matter = 2.5 um in diameter) levels as they dissipate from the exhaust fans of selected commercial, tunnel-ventilated, broiler houses in Northeast Georgia. PM2.5 was measured in real time using aerosol monitors and from a time-integrated basis using cyclone samplers. Ammonia was measured using open-path laser spectrometers. Data were taken over a 4-week period and filtered for wind direction and internal instrument calibration checks. Results indicate a rapid dissipation of both ammonia and fine particulates as the distance from the source increases. When compared to nearby monitoring data, particulate levels appear to be near background levels. Ammonia levels are higher when wind is blowing from the source toward the sensors and tend to be higher when wind speed is less than 3.2 km/h (2 mph.) At low wind speeds, air movement created by fans overpowers ambient wind at the 30-m distance.

Concentrated animal feeding operations are major sources of ammonia emitted to the atmosphere. There is a considerable literature on ammonia emissions from poultry and swine, but few studies have investigated large, open lot beef cattle feedyards. We used the micrometeorological flux-gradient method to estimate ammonia emissions during six field campaigns in three seasons. Profiles of ammonia, wind speed and air temperature were measured on towers located within feedyard pens. Atmospheric ammonia concentration was measured using either acid gas washing or chemiluminescence. Mean daily ammonia flux in summer averaged 72 µg m-2 s-1, and in winter, 39 µg m-2 s-1. Springtime fluxes were highly variable and averaged 79 µg m-2 s-1; high springtime fluxes were attributed to greater ammonium concentration in manure and high wind speeds. Ammonia-N emisson rate averaged 3930 and 2150 kg d-1 in summer and winter, respectively, which was 45% and 27% of fed N. Assuming that the mean of summer and winter emission rates represented a mean annual emission, ammonia-N loss was 36% of fed N, and an annual emission factor for feedyard pens based on total yearly per head production was 11.0 kg NH3-N head-1 yr-1. Ammonia emissions increased after N in cattle rations was increased from 13.5% to 14.5%. Ammonia emissions estimated using the flux-gradient method were 22 to 36% less than those derived from an inverse dispersion model. Uncertainty in the Schmidt number and possible violation of the assumption of homogeneous flow could have contributed to the lower flux estimates of the flux-gradient method. Optimizing fed N through practices such as phase feeding could help minimize ammonia emissions. Longer term, more continuous monitoring of ammonia emissions is needed to better define annual variability, emission rates and factors, and facilitate development of process models.

In animal production systems (poultry, beef, and swine), current production, storage, and disposal techniques present a challenge to manage wastes to minimize the emissions of trace gases within relatively small geographical areas. Physical and chemical parameters were measured on primary and secondary lagoons on three different swine farming systems, three replicates each, in the Central Great Basin of the United States to determine ammonia (NH3) emissions. Nutrient concentrations, lagoon water temperature, and micrometeorological data from these measurements were used with a published process model to calculate emissions. Annual cycling of emissions was determined in relation to climatic factors and wind speed was found the predominating factor when the lagoon temperatures were above about 3 degrees C. Total NH3 emissions increased in the order of smallest to largest: nursery, sow, and finisher farms. However, emissions on an animal basis increased from nursery animals being lowest to sow animals being highest. When emissions were compared to the amount of nitrogen (N) fed to the animals, NH3 emissions from sows were lowest with emissions from finisher animals highest. Ammonia emissions were compared to similar farm production systems in the humid East of the United States and found to be similar for finisher animals but had much lower emissions than comparable humid East sow production. Published estimates of NH3 emissions from lagoons ranged from 36 to 70% of feed input (no error range) compared to our emissions determined from a process model of 9.8% with an estimated range of +/-4%.

Ammonia (NH(3)) emissions from animal systems have become a primary concern for all of livestock production. The purpose of this research was to establish the relationship of nitrogen (N) emissions to specific components of swine production systems and to determine accurate NH(3) emission factors appropriate for the regional climate, geography, and production systems. Micrometeorological instrumentation and gas sensors were placed over two lagoons in North Carolina during 1997-1999 to obtain information for determining ammonia emissions over extended periods and without interfering with the surrounding climate. Ammonia emissions varied diurnally and seasonally and were related to lagoon ammonium concentration, acidity, temperature, and wind turbulence. Conversion of significant quantities of ammonium NH(4)(+) to dinitrogen gas (N(2)) were measured in all lagoons with the emission rate largely dependent on NH(4)(+) concentration. Lagoon NH(4)(+) conversion to N(2) accounted for the largest loss component of the N entering the farm (43% as N(2)); however, small amounts of N(2)O were emitted from the lagoon (0.1%) and from field applications (0.05%) when effluent was applied nearby. In disagreement with previous and current estimates of NH(3) emissions from confined animal feeding operation (CAFO) systems, and invalidating current assumptions that most or all emissions are in the form of NH(3), we found much smaller NH(3) emissions from animal housing (7%), lagoons (8%), and fields (2%) using independent measurements of N transformation and transport. Nitrogen input and output in the production system were evaluated, and 95% of input N was accounted for as output N from the system.

Land application of poultry litter can provide essential plant nutrients for crop production, but ammonia (NH(3)) volatilization from the litter can be detrimental to the environment. A multiseason study was conducted to quantify NH(3) volatilization rates from surface-applied poultry litter under no-till and paraplowed conservation tillage managements. Litter was applied to supply 90 to 140 kg N ha(-1). Evaluation of NH(3) volatilization was determined using gas concentrations and the flux-gradient gas transport technique using the momentum balance transport coefficient. Ammonia fluxes ranged from 3.3 to 24% of the total N applied during the winter and summer, respectively. Ammonia volatilization was rapid immediately after litter application and stopped within 7 to 8 d. Precipitation of 17 mm essentially halted volatilization, probably by transporting litter N into the soil matrix. Application of poultry to conservation-tilled cropland immediately before rainfall events would reduce N losses to the atmosphere but could also increase NO(3) leaching and runoff to streams and rivers.

Methane (CH4) emissions from animals represent a significant contribution to anthropogenically produced radiatively active trace gases. Global and national CH4 budgets currently use predictive models based on emission data from laboratory experiments to estimate the magnitude of the animal source. This paper presents a method for measuring CH4 from animals under undisturbed field conditions and examines the performance of common models used to simulate field conditions. A micrometeorological mass difference technique was developed to measure CH4 production by cattle in pasture and feedlot conditions. Measurements were made continuously under field conditions, semiautomatically for several days, and the technique was virtually nonintrusive. The method permits a relatively large number of cattle to be sampled. Limitations include light winds (less than approximately 2 m/s), rapid wind direction changes, and high-precision CH4 gas concentration measurement. Methane production showed a marked periodicity, with greater emissions during periods of rumination as opposed to grazing. When the cattle were grazed on pasture, they produced .23 kg CH4 x animal(-1) x d(-1), which corresponded to the conversion of 7.7 to 8.4% of gross energy into CH4. When the same cattle were fed a highly digestible, high-grain diet, they produced .07 kg CH4 x animal(-1) x d(-1), corresponding to a conversion of only 1.9 to 2.2% of the feed energy to CH4. These measurements clearly document higher CH4 production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets. The mass difference method provides a useful tool for "undisturbed" measurements on the influence of feedstuffs and nutritional management practices on CH4 production from animals and for developing improved management practice for enhanced environmental quality.