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Atmospheric Environment (v.42, #14)
Workshop on Agricultural Air Quality: State of the science by Viney P. Aneja; Jessica Blunden; Paul A. Roelle; William H. Schlesinger; Raymond Knighton; Dev Niyogi; Wendell Gilliam; Greg Jennings; Clifford S. Duke (pp. 3195-3208).
The first Workshop on Agricultural Air Quality: State of the Science was held at the Bolger Center in Potomac, Maryland from 4 to 8 June 2006. This international conference assembled approximately 350 people representing 25 nations from 5 continents, with disciplines ranging from atmospheric chemistry to soil science. The workshop was designed as an open forum in which participants could openly exchange the most current knowledge and learn about numerous international perspectives regarding agricultural air quality. Participants represented many stakeholder groups concerned with the growing need to assess agricultural impacts on the atmosphere and to develop beneficial policies to improve air quality. The workshop focused on identifying methods to improve emissions inventories and best management practices for agriculture. Workshop participants also made recommendations for technological and methodological improvements in current emissions measurement and modeling practices.The workshop commenced with a session on agricultural emissions and was followed by international perspectives from the United States, Europe, Australia, India, and South America. This paper summarizes the findings and issues of the workshop and articulates future research needs. These needs were identified in three general areas: (1) improvement of emissions measurement; (2) development of appropriate emission factors; and (3) implementation of best management practices (BMPs) to minimize negative environmental impacts. Improvements in the appropriate measurements will inform decisions regarding US farming practices. A need was demonstrated for a national/international network to monitor atmospheric emissions from agriculture and their subsequent depositions to surrounding areas. Information collected through such a program may be used to assess model performance and could be critical for evaluating any future regulatory policies or BMPs. The workshop concluded that efforts to maximize benefits and reduce detrimental effects of agricultural production need to transcend disciplinary, geographic, and political boundaries. Also, such efforts should involve natural and social scientists, economists, engineers, business leaders, and decision makers. The workshop came to the conclusion that through these collaborative efforts improvements in air quality from agricultural practices will begin to take effect.
Keywords: Nitrogen; Ammonia; Sulfur; Hydrocarbons; Biogenic VOCs; Odor; Emissions; Emission factor; Transport; Transformation; Crop and animal agriculture; Measurements; Modeling; Best Management Practices; Policy
Agricultural air quality in Europe and the future perspectives by Jan Willem Erisman; Albert Bleeker; Arjan Hensen; Alex Vermeulen (pp. 3209-3217).
Agricultural emissions in Europe are important to several atmospheric transport-related environmental issues. These include local and regional air quality problems, such as PM exposure, eutrophication and acidification, toxics and contribution to greenhouse gas emissions, resulting in a number of environmental impacts. Over Europe, agricultural emissions are variable in space and time and the contribution to the different issues are variable. Most important are ammonia (90%), PM (20%) and methane and nitrous oxide (both 5%). Policies have been developed to combat some of the emissions with success in some countries. However, future, national and European policies are necessary to successfully decrease emissions and its related problems. Current research issues include the quantification of non-point sources, the atmosphere–biosphere exchange of ammonia, the quantification of landscape processes and the primary and secondary emissions of PM.
Keywords: Air quality; Agriculture; Europe; Emission; Greenhouse gas; Nitrogen; Ammonia; Particulate matter
Modeling agricultural air quality: Current status, major challenges, and outlook by Yang Zhang; S.-Y. Shiang-Yuh Wu; Srinath Krishnan; Kai Wang; Ashley Queen; Viney P. Aneja; S. Pal Arya (pp. 3218-3237).
Agricultural air quality is an important emerging area of atmospheric sciences that represents significant challenges in many aspects of research including measurements, modeling, regulations, emission control, and operation managements. This work presents a review of current status, major challenges, and future research needs and opportunities of several important aspects of agricultural air quality modeling including chemical species, concentration and deposition measurements for model verification, emission inventories, major physical and chemical processes, model application and evaluation, and policy implications.
Keywords: Agriculture; Air quality; Ammonia; Reduced nitrogen; 3-D modeling
Trends in agricultural ammonia emissions and ammonium concentrations in precipitation over the Southeast and Midwest United States by Konarik Stephen; Viney P. Aneja (pp. 3238-3252).
Emissions from agricultural activities, both crop and animal, are known to contain gaseous ammonia (NH3) which through chemical reaction in rainwater changes into ammonium ion (NH4+). Using wet deposition data of ammonium from several National Atmospheric Deposition Program/National Trends Network (NADP/NTN) and ambient levels of ammonium from Clean Air Status Trends Network (CAST Net) sites as well as calculated NH3 emissions from North Carolina, and the Southeast and Midwest regions of the United States, trends in ammonium concentrations in precipitation were analyzed for the period of 1983–2004. The beginning of 1997 coincides with the implementation of a swine population moratorium in the state of North Carolina. Results from the analysis in North Carolina indicate a lessening in the rate of increases in NH4+ concentration in precipitation since the moratorium went into effect. Sampson County, NC, saw stable NH4+ concentrations from 1983 to 1989, an average rise of 9.5% from 1989 to 1996, and an average increase of only 4% from 1997 to 2004. In addition, HYSPLIT back-trajectory model was used to determine that when ambient air in downwind sites arrived from the high NH3 emissions source region, ammonium concentrations in precipitation were enhanced. For the Southeast United States domain, analysis shows that NH4+ concentrations generally increased with increasing NH3 emissions from within the same region. Similar analysis has been performed over the Midwest United States and compared to the results from the Southeast United States. Emissions from the Midwest are attributed to larger animals, including hogs and cattle, whereas the Southeast has a higher percentage of emissions coming from smaller livestock, such as chickens. In addition, the states of the Midwest United States have a much more uniform spatial distribution of emissions.
Keywords: Ammonia emissions; North Carolina hog moratorium; Ammonium wet deposition
Improved temporal resolution in process-based modelling of agricultural soil ammonia emissions by J.D. Beuning; E. Pattey; G. Edwards; B.J. Van Heyst (pp. 3253-3265).
An emerging environmental issue in Canada is how to quantify the contribution of agricultural soil emissions of ammonia (NH3) to environmental pollution. Emission inventories are essential to predict these emissions and their subsequent atmospheric transportation, transformation, and deposition. Due to the high spatial and temporal variability associated with NH3 emissions, emission inventories based on measurements become expensive and emission factors lose accuracy. Process-based models are capable of accounting for the complex soil interactions, but current models lack temporal refinement and few models consider NH3 emissions. This paper presents the development of a one-dimensional (vertical), time-dependent model capable of predicting NH3 emissions from a slurry applied to a bare soil. The model is based on chemical, physical and biological relationships that govern soil heat, moisture, and nitrogen movement. Processes considered include convection, diffusion, decomposition, nitrification, denitrification, and surface to atmosphere transport. The model is tested with experimental data from Agriculture and Agri-Food Canada which conducted NH3 measurements following application of dairy cattle slurry to a bare field. An investigation into the sensitivity of emissions to pH and slurry infiltration rate is conducted and model predictions are best fit to measurements based on this investigation. Testing demonstrated the model's ability to predict the large NH3 emissions immediately following application and subsequent emission trends associated with diurnal patterns that emission factors cannot capture. Results showed that model performance could benefit from a more in depth measurement program and empirical or process models of surface pH. Potential exists for the model to become a useful tool in predicting emissions on local, regional, or national scales.
Keywords: Ammonia volatilization; Bare soil; Process-based model; Slurry application; Total ammoniacal nitrogen
A new Swiss inventory of ammonia emissions from agriculture based on a survey on farm and manure management and farm-specific model calculations by Beat Reidy; Beat Rhim; Harald Menzi (pp. 3266-3276).
Existing emission inventory approaches mainly rely on expert judgement for information on farm and manure management. To detect the relatively small changes of total annual ammonia (NH3) emissions required under the Gothenburg Protocol, expert judgement is considered insufficient. We present, therefore, here a new Swiss NH3 emission inventory based on a detailed representative stratified survey on farm and manure management conducted on 1950 farms. The survey data was used to calculate NH3 emissions with the emission model DYNAMO for each farm participating in the survey. This allowed the effects of the variability of farm and manure management parameters among farms on the NH3 emissions to be fully taken into account. Weighted emission factors per animal for 24 livestock categories and 36 farm classes were used to upscale to the national inventory. The stratified sampling and the individual farm calculations allowed the comparison of emissions from specific regions and altitudes and the study of the variability among farms. The new emission inventory approach permits a more detailed analysis of the regional distribution of NH3 emissions as well as a more robust and standardised monitoring of the future development of emissions.
Keywords: Ammonia; Emission; Inventory; N-flow; Management; Survey
Characterizing ammonia and hydrogen sulfide emissions from a swine waste treatment lagoon in North Carolina by Jessica Blunden; Viney P. Aneja (pp. 3277-3290).
Emissions of atmospheric ammonia–nitrogen (NH3-N, where NH3-N=(14/17)NH3) and hydrogen sulfide (H2S) from a commercial anaerobic swine waste treatment lagoon (17,150m2 at normal liquid level) were measured over a 1-year period. Continuous simultaneous measurements were made at the lagoon using a dynamic flow-through chamber system for ∼1 week during four seasons, October–November 2004 (fall), February 2005 (winter), April 2005 (spring), and June 2005 (summer) in an effort to examine diurnal and seasonal variability, and the respective relationships of NH3-N and H2S emissions to lagoon physicochemical properties. Continuously measured lagoon physicochemical parameters include lagoon surface temperature and lagoon pH. Aqueous lagoon samples were collected daily and analyzed for total Kjeldahl nitrogen (TKN), total ammoniacal nitrogen (TAN), and total sulfide concentration. TKN, TAN, and sulfide concentrations ranged from 400–650, 360–590, and 0.1–13.0mgL−1, respectively. For NH3-N, the largest fluxes were observed during the summer (>4200μg Nm−2min−1). During the fall and spring, average NH3-N fluxes were 1634±505 and >2495μg Nm−2min−1, respectively. The lowest fluxes were observed during the winter where average flux values were 1290±246μg Nm−2min−1. Fluxes for H2S were negligible during the winter season. Average fluxes increased during the fall (0.3±0.1μgm−2min−1) and spring (0.5±1.0μgm−2min−1), and highest flux values were observed during the summer (5.3±3.2μgm−2min−1). The seasonal NH3-N and H2S emission factors ranged from ∼10 to ∼40kg NAU−1yr−1 (1AU=500kg live animal weight) and ∼0 to ∼0.05kg H2SAU−1yr−1, respectively. Generally, the lagoon emissions for H2S were ∼3–4 orders of magnitude less than NH3-N. The gas fluxes were related to various physicochemical parameters including the pH and near-surface temperature of the lagoon, and the aqueous concentration of the respective gas.
Keywords: Ammonia; Hydrogen sulfide; Emissions; Dynamic chamber; Pig manure; Lagoon
Characterizing ammonia emissions from swine farms in eastern North Carolina: Reduction of emissions from water-holding structures at two candidate superior technologies for waste treatment by Viney P. Aneja; S. Pal Arya; Ian C. Rumsey; D-S. Kim; K.S. Bajwa; C.M. Williams (pp. 3291-3300).
Program OPEN (Odor, Pathogens, and Emissions of Nitrogen) was an integrated study of the emissions of ammonia (NH3), odor and odorants, and pathogens from potential environmentally superior technologies (ESTs) for swine facilities in eastern North Carolina. This paper, as part of program OPEN, focuses on quantifying emissions of NH3 from water-holding structures at two of the best ESTs and compares them with the projected emissions from two conventional lagoon and spray technologies (LSTs). The evaluated ESTs are: (1) Super Soils at Goshen Ridge; and (2) Environmental Technologies at Red Hill. The water-holding structures for these two ESTs contained no conventional anaerobic lagoon. A dynamic flow-through chamber was used to measure NH3 fluxes from the water-holding structures at both the ESTs and at the conventional LST farms. In order to compare the emissions from the water-holding structures at the ESTs with those from the lagoons at the conventional sites under similar conditions, a statistical-observational model for lagoon NH3 emissions was used. A mass-balance approach was used to quantify the emissions. All emissions were normalized by nitrogen-excretion rates. The percentage reductions relative to the conventional lagoons were calculated for the two ESTs. Results showed substantial reductions in NH3 emissions at both ESTs. Super Soils had reductions of 94.7% for the warm season and 99.0% for the cool season. Environmental Technologies had slightly larger reductions of 99.4% and 99.98% for the cool and warm season, respectively. As a result of such large reductions in ammonia emissions, both technologies meet the criteria to be classified as ESTs for ammonia emissions.
Keywords: Ammonia emissions; Ammonia flux; Water-holding structures; Environmentally superior technologies (ESTs); Lagoon and spray technologies (LSTs)
Air-flow distortion and turbulence statistics near an animal facility by J.H. Prueger; W.E. Eichinger; L.E. Hipps; J.L. Hatfield; D.I. Cooper (pp. 3301-3314).
The emission and dispersion of particulates and gases from concentrated animal feeding operations (CAFO) at local to regional scales is a current issue in science and society. The transport of particulates, odors and toxic chemical species from the source into the local and eventually regional atmosphere is largely determined by turbulence. Any models that attempt to simulate the dispersion of particles must either specify or assume various statistical properties of the turbulence field. Statistical properties of turbulence are well documented for idealized boundary layers above uniform surfaces. However, an animal production facility is a complex surface with structures that act as bluff bodies that distort the turbulence intensity near the buildings. As a result, the initial release and subsequent dispersion of effluents in the region near a facility will be affected by the complex nature of the surface. Previous Lidar studies of plume dispersion over the facility used in this study indicated that plumes move in complex yet organized patterns that would not be explained by the properties of turbulence generally assumed in models. The objective of this study was to characterize the near-surface turbulence statistics in the flow field around an array of animal confinement buildings. Eddy covariance towers were erected in the upwind, within the building array and downwind regions of the flow field. Substantial changes in turbulence intensity statistics and turbulence-kinetic energy (TKE) were observed as the mean wind flow encountered the building structures. Spectra analysis demonstrated unique distribution of the spectral energy in the vertical profile above the buildings.
Keywords: Turbulence; Transport; Boundary layer; CAFO
Measurement and analysis of ammonia and hydrogen sulfide emissions from a mechanically ventilated swine confinement building in North Carolina by Jessica Blunden; Viney P. Aneja; Phillip W. Westerman (pp. 3315-3331).
Emissions of atmospheric ammonia–nitrogen (NH3–N, where NH3–N=(1417)NH3) and hydrogen sulfide (H2S) were measured from a finishing swine confinement house at a commercial pig farm in eastern North Carolina. Continuous simultaneous NH3–N and H2S emissions were made for ∼1-week period during four different seasons. The number of pigs contained in the house varied from ∼850 to 900 with average weights ranging from ∼38 to 88kg. Average NH3–N concentrations were highest during the winter and spring sampling periods, 8.91±4.61 and 8.44±2.40ppm, respectively, and lower during the summer and fall, 2.45±1.14 and 4.27±0.71ppm, respectively. Measured average H2S concentrations were 673±282, 429±223, 47±18, and 304±88ppb during winter, spring, summer, and fall, respectively. Generally, the H2S concentrations were approximately an order of magnitude less than NH3–N during winter, spring, and fall, and two orders of magnitude smaller during the summer season.The average ambient temperature ranged from 5.5 to 22.3°C while the average barn temperature measured at the outlet fans ranged from 19.0 to 26.0°C in the winter and summer, respectively. The average fan ventilation rates varied from 253m3min−1 during the fall sampling period to 1024m3min−1 during summer.Calculated total emission rates for both NH3–N and H2S were highest during the spring, 4519±1639gNday−1 and 481±142gday−1, respectively. Emissions were lowest during the fall season for NH3–N (904±568gNday−1) and the summer season for H2S (82±49gday−1). Normalized NH3–N emission rates were highest in winter and spring (33.6±21.9 and 30.6±11.1gNday−1AU−1, where 1AU (animal unit)=500kg) and lowest during summer and fall (24.3±12.4 and 11.8±7.4gNday−1AU−1). Normalized H2S emissions were highest during the winter and spring seasons (4.2±2.1 and 3.3±1.0gday−1AU−1) and were lowest in summer and fall (1.2±0.7 and 1.7±0.5gday−1AU−1).
Keywords: Ammonia; Hydrogen sulfide; Swine barns; CAFOs
Field sampling method for quantifying volatile sulfur compounds from animal feeding operations by Steven Trabue; Kenwood Scoggin; Frank Mitloehner; Hong Li; Robert Burns; Hongwei Xin (pp. 3332-3341).
Volatile sulfur compounds (VSCs) are a major class of chemicals associated with odor from animal feeding operations (AFOs). Identifying and quantifying VSCs in air is challenging due to their volatility, reactivity, and low concentrations. In the present study, a canister-based method collected whole air in fused silica-lined (FSL) mini-canister (1.4L) following passage through a calcium chloride drying tube. Sampled air from the canisters was removed (10–600mL), dried, pre-concentrated, and cryofocused into a GC system with parallel detectors (mass spectrometer (MS) and pulsed flame photometric detector (PFPD)). The column effluent was split 20:1 between the MS and PFPD. The PFPD equimolar sulfur response enhanced quantitation and the location of sulfur peaks for mass spectral identity and quantitation. Limit of quantitation for the PFPD and MSD was set at the least sensitive VSC (hydrogen sulfide) and determined to be 177 and 28pgS, respectively, or 0.300 and 0.048μgm−3 air, respectively. Storage stability of hydrogen sulfide and methanethiol was problematic in warm humid air (25°C, 96% relative humidity (RH)) without being dried first, however, stability in canisters dried was still only 65% after 24h of storage. Storage stability of hydrogen sulfide sampled in the field at a swine facility was over 2 days. The greater stability of field samples compared to laboratory samples was due to the lower temperature and RH of field samples compared to laboratory generated samples. Hydrogen sulfide was the dominant odorous VSCs detected at all swine facilities with methanethiol and dimethyl sulfide detected notably above their odor threshold values. The main odorous VSC detected in aged poultry litter was dimethyl trisulfide. Other VSCs above odor threshold values for poultry facilities were methanethiol and dimethyl sulfide.
Keywords: Volatile sulfur compounds; Animal feeding operations; CAFO; OdorAbbreviations; AFO; animal feeding operation; VSC; volatile sulfur compound; PFPD; pulsed flame photometric detector; RH; relative humidity; FSL; fused silica lined; OAV; odor activity value; ppmv; parts-per-million volume; ppbv; parts-per billion volume; SPME; solid phase microextraction.
U.S. broiler housing ammonia emissions inventory by R.S. Gates; K.D. Casey; E.F. Wheeler; H. Xin; A.J. Pescatore (pp. 3342-3350).
Using recently published baseline ammonia emissions data for U.S. broiler chicken housing, we present a method of estimating their contribution to an annual ammonia budget that is different from that used by USEPA. Emission rate increases in a linear relationship with flock age from near zero at the start of the flock to a maximum at the end of the flock, 28–65 days later. Market weight of chickens raised for meat varies from “broilers” weighing about 2kg to “roasters” weighing about 3kg. Multiple flocks of birds are grown in a single house annually, with variable downtime to prepare the house between flocks. The method takes into account weight and number of chickens marketed. Uncertainty in baseline emissions estimates is used so that inventory estimates are provided with error estimates. The method also incorporates the condition of litter that birds are raised upon and the varying market weight of birds grown. Using 2003 USDA data on broiler production numbers, broiler housing is estimated to contribute 8.8–11.7kT ammonia for new and built-up litter, respectively, in Kentucky and 240–324kT ammonia for new and built-up litter, respectively, nationally. Results suggest that a 10% uncertainty in annual emission rate is expected for the market weight categories of broilers, heavy broilers, and roasters. A 27–47% reduction in annual housing emission rate is predicted if new rather than built-up litter were used for every flock. The estimating method can be adapted to other meat bird building emissions and future ammonia emission strategies, with suitable insertion of an age-dependent emission factor or slope into a predictive model equation. The method can be readily applied and is an alternative to that used by USEPA.
Keywords: Agricultural air quality; Poultry; Environment
Winter broiler litter gases and nitrogen compounds: Temporal and spatial trends by D.M. Miles; D.E. Rowe; P.R. Owens (pp. 3351-3363).
Understanding how animal activities, management, and barn structure affect litter gases and nutrients is fundamental to developing accurate emission models for meat-bird facilities. This research characterized the temporal and spatial variability of litter ammonia (NH3) and nitrous oxide (N2O) flux via a chamber method, as well as determined litter nitrogen (N) compounds by intensive sampling in two commercial broiler houses on aged litter. Thirty-six grid samples were taken during a winter flock in Mississippi on days 2, 22, and 45. On day 45, eight additional samples were taken near the feeders and waterers (F/W). Geostatistical contour plots indicate NH3 flux on day 2 was elevated in the brood area of house one (H1) where litter and air temperatures were highest; a commercial litter treatment held the NH3 flux near zero for approximately 45% of the brood area in house two (H2). Day 45 NH3 fluxes were similar, averaging 694mgm−2h−1 in H1 vs. 644mgm−2h−1 in H2; both houses exhibited greater NH3 flux near the cooling pads. Ammonia flux, litter moisture and pH were diminished at the F/W locations. Heavy cake near the exhaust fans provided the lowest recorded litter pH, highest litter moisture and ammonium (NH4) with no NH3 flux at the flock's end. Trends in litter condition based on bird activity were evident, but individual differences persisted between the houses. The importance of cake formation over the litter surface and differences based on location, both related to bird activity and house structure, should be considered in NH3 mitigation strategies.
Keywords: Ammonia; Broiler; Cake; Litter
Measurement and modeling of atmospheric flux of ammonia from dairy milking cow housing by Brian Rumburg; George H. Mount; Jenny Filipy; Brian Lamb; Hal Westberg; David Yonge; Ron Kincaid; Kristen Johnson (pp. 3364-3379).
Atmospheric ammonia(NH3) measurements are needed to better understand the impacts ofNH3 emissions on aerosol formation and concentrations and anthropogenic changes to the N cycle. This paper describes concentration measurements ofNH3 using differential optical absorption spectroscopy (DOAS), tracer ratio flux experiments, and development of aNH3 emissions model from a dairy milking cow free stall house with concrete floors. An area source tracer gas ratio method was used to determineNH3 fluxes which involved releasingSF6 as the tracer gas from the upwind edge of the stalls and measuring the tracer concentration downwind along with the DOASNH3 measurements. The flux is calculated from the ratio of theNH3 andSF6 concentrations and theSF6 release rate and taking into account the differences in area and dispersion. The measured stall flux for the summers averaged29±19gNH3cow-1h-1 at an average temperature of18±5∘C. The emissions model calculated liquidNH3 concentrations in urine puddles,NH3 volatilization, theoretical and empirical mass transfer to the bulk atmosphere, andNH3 transport. The predicted concentrations were within±30% using an empirical mass transfer coefficient and within±41% using a theoretical mass transfer coefficient. Total annualNH3 emissions for the dairy of 185 milking cows was 7400kg or40kgNH3cow-1year-1, estimated total N excretions are180kgcow-1year-1. This agrees with a N mass balance of the dairy. The model was very sensitive to urine puddle pH and also showed that emissions are temperature dependent.
Keywords: Ammonia; Emission; Dairy; Tracer gas
Measurements and modeling of atmospheric flux of ammonia from an anaerobic dairy waste lagoon by B. Brian Rumburg; George H. Mount; David Yonge; Brian Lamb; Hal Westberg; Manjit Neger; Jenny Filipy; Ron Kincaid; Kristen Johnson (pp. 3380-3393).
Atmospheric anthropogenic ammonia(NH3) emissions are not well understood in the US due to a lack of measurement data from the main emission sources. This paper describes concentration measurements downwind of an anaerobic dairy waste lagoon using differential optical absorption spectroscopy (DOAS), tracer ratio flux experiments and the testing of two mechanistic emission models. The tracer ratio method involves releasing a measured flux of a tracer gas upwind of the lagoon and measuring the concentration downwind along with the DOASNH3 measurement. The flux is calculated by ratioing the tracer flux and concentration with theNH3 concentration and taking into account the differences in area and dispersion over the area source. Measured fluxes from the tracer experiments ranged from0.11gm-2h-1 at an air temperature of11∘C to0.54gm-2h-1 at an air temperature of27∘C. TheNH3 emission models were based upon the temperature-dependent biological activity, the partitioning ofNH3 andNH4+ in solution, and the partitioning ofNH3 between the gas and liquid phases. The theoretical mechanistic model and the empirical mechanistic model had normalized mean errors of 120% and 21%, respectively, when compared to measurements. Emissions were most sensitive to changes in lagoon pH. Annual emissions were55kgNH3cow-1yr-1 from all lagoons, estimated excretion is180kgNcow-1yr-1. Using literature lagoon design criteria to estimate lagoon size resulted in an underestimation of emissions of-29%.
Keywords: Ammonia; Emission; Dairy; Tracer gas
Gas exchange between plant canopies and the atmosphere: Case-studies for ammonia by O.T. Denmead; J.R. Freney; F.X. Dunin (pp. 3394-3406).
We first present the elements of an inverse Lagrangian model of gas transport in plant canopies. The model allows the inference of sites of gas exchange in the canopy and their source and sink strengths from measured profiles of mean gas concentration and statistics of the canopy turbulence. The practical application of the model is demonstrated through a case study of the fate of ammonia volatilized from fertilizer applied to the floor of a sugarcane crop. Some of the lost ammonia was absorbed by the foliage of the crop; the rest was lost to the atmosphere above. While there was excellent agreement between model predictions of the net flux from the canopy and independent micrometeorological measurements of ammonia flux in the air-layer above it, verification of flux predictions within the canopy was much more difficult. Appeal was made to a process-based model of canopy gas exchange that describes gas transport to and from foliage surfaces in terms of diffusion across aerodynamic, boundary-layer and stomatal resistances in response to a difference in ammonia concentration between the air and leaf sub-stomatal cavities. There was acceptable agreement between the two models in their predictions of foliage ammonia uptake. Next, we apply the process model to a study of the recapture of volatilized ammonia by sugarcane crops with different leaf area indices (LAI). The study indicated recoveries increasing almost linearly with LAI and suggested probable recoveries in excess of 20% for canopies with LAIs of 2 or more. These and other published studies of ammonia exchange between canopy and atmosphere that employed both the inverse Lagrangian and process models suggest that their coupling provides a powerful tool for studying canopy gas exchange.
Keywords: Micrometeorology; Lagrangian dispersion; Ammonia; Compensation point: Resistance-analogue models
Inferential model estimates of ammonia dry deposition in the vicinity of a swine production facility by John Walker; Porche’ Spence; Sue Kimbrough; Wayne Robarge (pp. 3407-3418).
This project investigates NH3 dry deposition around a commercial swine production facility in eastern North Carolina. Passive diffusion-tube samplers were used to measure weekly integrated NH3 concentrations at 22 locations along horizontal gradients from the barn/lagoon emissions complex (source) out to a distance of 700m. A two-layer canopy compensation point model was used to predict bi-directional NH3 exchange within a 500m circular buffer surrounding the source. The model takes into account differences in soil and vegetation emission potential, as well as canopy physical characteristics, among three primary surfaces surrounding the site: forest, crops spray fertilized with swine waste, and other fertilized crops. Between June 2003 and July 2005, mean observed NH3 concentrations ranged from 169.0μg NH3m−3 at a distance of 10m from the source to 7.1 and 13.0μg NH3m−3 at 612 and 698m in the predominant upwind and downwind directions, respectively. Median predicted dry deposition rates ranged from 145kg NH3–Nha−1yr−1 at 10m from the source to 16kg NH3–Nha−1yr−1 at 500m, which is ≈3.5× wet deposition of NH4+–N. Assuming a steady-state emission factor of 7.0kg NH3animal−1yr−1 and a median population of 4900 animals, NH3 dry deposition over the nearest 500m from the barn/lagoon complex accounted for 10.4% (3567kg NH3) of annual emissions (34,300kgNH3). A model sensitivity analysis shows that predicted deposition rates are more sensitive to assumptions regarding cuticular uptake relative to soil and vegetation emission potentials.
Keywords: Ammonia; Bi-directional flux; Compensation point; Dry deposition; Resistance model
Modeling atmospheric transport and fate of ammonia in North Carolina—Part I: Evaluation of meteorological and chemical predictions by Shiang-Yuh Wu; Srinath Krishnan; Yang Zhang; Viney Aneja (pp. 3419-3436).
The atmospheric transport and fate of ammonia (NH3) depend on both meteorological and chemical conditions once it is emitted into the atmosphere. The largest source contributing to NH3 emission is the agricultural production, in particular animal operation, in North Carolina (NC). In this study, three-dimensional numerical meteorological and air quality models are applied to study the transport and fate of NH3 in the atmosphere in an area in southeast US centered over NC. One summer and one winter month simulations with a 4-km horizontal grid were conducted to simulate the meteorological and chemical environments for the transport and transformation of the reduced nitrogen, NH x (=NH3+NH4+) and to examine its seasonal variations and interactions with other chemical species (e.g., ozone and fine particular matter, PM2.5). The model performance for simulated meteorology and air quality was evaluated against observations in terms of spatial distributions, temporal variations, and statistical trends.MM5/CMAQ gave an overall good performance for meteorological variables and O3 mixing ratios and a reasonably good performance for PM2.5. The simulations show that 10–40% of total NH3 was converted to NH4+ at/near source and 40–100% downwind in August, and the conversion rates were 20–50% at/near source and 50–98% downwind in December. While the 3-D atmospheric models demonstrate some skills in capturing synoptic meteorological patterns, diurnal variations of concentrations of oxidants and PM2.5, and regional transport and transformation of NH x, reproducing meteorological and chemical features at a local scale and the magnitudes of hourly concentrations of oxidants and PM2.5 remain challenging due to uncertainties in model inputs and treatments.
Keywords: Ammonia; Transport and fate; North Carolina; Model evaluation; CMAQ; MM5
Modeling atmospheric transport and fate of ammonia in North Carolina—Part II: Effect of ammonia emissions on fine particulate matter formation by S.-Y. Shiang-Yuh Wu; J.-L. Jian-Lin Hu; Yang Zhang; Viney P. Aneja (pp. 3437-3451).
Accurate estimates of ammonia (NH3) emissions are needed for reliable predictions of fine particulate matter (PM2.5) by air quality models (AQMs), but the current estimates contain large uncertainties in the temporal and spatial distributions of NH3 emissions. In this study, the US EPA Community Multiscale Air Quality (CMAQ) modeling system is applied to study the contributions of the agriculture–livestock NH3 (AL-NH3) emissions to the concentration of PM2.5 and the uncertainties in the total amount and the temporal variations of NH3 emissions and their impact on the formation of PM2.5 for August and December 2002.The sensitivity simulation results show that AL-NH3 emissions contribute significantly to the concentration of PM2.5, NH4+, and NO3−; their contributions to the concentrations of SO42− are relatively small. The impact of NH3 emissions on PM2.5 formation shows strong spatial and seasonal variations associated with the meteorological conditions and the ambient chemical conditions. Increases in NH3 emissions in August 2002 resulted in >10% increases in the concentrations of NH4+ and NO3−; reductions in NH3 emissions in December 2002 resulted in >20% decreases in their concentrations. The large changes in species concentrations occur downwind of the high NH3 emissions where the ambient environment is NH3-poor or neutral. The adjustments in NH3 emissions improve appreciably the model predictions of NH4+ and NO3− both in August and December, but resulted in negligible improvements in PM2.5 in August and a small improvement in December, indicating that other factors (e.g., inaccuracies in meteorological predictions, emissions of other primary species, aerosol treatments) might be responsible for model biases in PM2.5.
Keywords: Ammonia emissions; Agriculture; Livestock; PM; 2.5; CMAQ; Sensitivity study
Comparison of models used for national agricultural ammonia emission inventories in Europe: Liquid manure systems by B. Reidy; Dammgen U. Dämmgen; Dohler H. Döhler; B. Eurich-Menden; F.K. van Evert; N.J. Hutchings; H.H. Luesink; H. Menzi; T.H. Misselbrook; G.-J. Monteny; J. Webb (pp. 3452-3464).
Ammonia (NH3) emissions from agriculture commonly account for >80% of the total NH3 emissions. Accurate agricultural NH3 emission inventories are therefore required for reporting within the framework of the Gothenburg Protocol of the UN Convention on Long-range Transboundary Air Pollution. To allow a co-ordinated implementation of the Protocol, different national inventories should be comparable. A core group of emission inventory experts therefore developed a network and joint programme to achieve a detailed overview of the best inventory techniques currently available and compiled and harmonized the available knowledge on emission factors (EFs) for nitrogen (N)-flow emission calculation models and initiated a new generation of emission inventories. As a first step in summarizing the available knowledge, six N-flow models, used to calculate national NH3 emissions from agriculture in different European countries, were compared using standard datasets. Two scenarios for slurry-based systems were run separately for dairy cattle and for pigs, with three different levels of model standardisation: (a) standardised inputs to all models (FF scenario); (b) standard N excretion, but national values for EFs (FN scenario); (c) national values for N excretion and EFs (NN scenario). Results of the FF scenario showed very good agreement among models, indicating that the underlying N flows of the different models are highly similar. As a result of the different national EFs and N excretion rates, larger differences among the results were observed for the FN and the NN scenarios. Reasons for the differences were primarily attributed to differences in the agricultural practices and climatic factors reflected in the EFs and the N excretion rates. The scientific debate necessary to understand the variation in the results generated awareness and consensus concerning available scientific data and the importance of specific processes not yet included in some models.
Keywords: Inventory; Ammonia; Emission; Emission factor; N-flow model