Measurements and Modeling of Emissions , Dispersion and Dry

BAJWA, KANWARDEEP SINGH. Measurements and Modeling of Emissions, Dispersion and Dry Deposition of Ammonia from Swine Facilities. (Under the direction of Dr. Viney P. Aneja and Dr. S. Pal Arya). Ammonia has recently gained importance for its increasing atmospheric concentrations and its role in the formation of aerosols. Studies have shown increasing atmospheric concentration levels of NH3 and NH4 , especially in the regions of concentrated animal feeding operations. Atmospheric inputs of reduced nitrogen as ammonia and ammonium by dry and wet deposition may represent a substantial contribution to the acidification of semi natural ecosystems and could also affect sensitive coastal ecosystems and estuaries. The anaerobic lagoon and spray method, commonly used for waste storage and disposal in confined animal feeding operations (CAFO), is a significant source of ammonia emissions. An accurate emission model for ammonia from aqueous surfaces can help in the development of emission factors. Study of dispersion and dry deposition patterns of ammonia downwind of a hog farm will help us to understand how much ammonia gets dry deposited near the farm, and how remaining ammonia gets transported farther away. An experimental and modeling study is conducted of emissions, dispersion and dry deposition of ammonia taking one swine farm as a unit. Measurements of ammonia flux were made at 11 swine facilities in North Carolina using dynamic flow-through chamber system over the anaerobic waste treatment lagoons. Continuous measurements of ammonia flux, meteorological and lagoon parameters were made for 8-10 days at each farm during each of the warm and cold seasons. Ammonia concentrations were continuously measured in the chamber placed over the lagoon using a Thermo Environmental Instrument Incorporated (TECO) Model 17c chemiluminescnce ammonia analyzer. A similar ammonia analyzer was used to measure ammonia concentrations at selected locations on the farm. Barn emissions were measured using open-path Fourier transform infrared (OP-FTIR) spectroscopy. A 10 m meteorological tower was erected at each site to measure wind speed and direction, temperature, relative humidity and solar radiation. Data collected from field measurements made at hog waste lagoons in south eastern North Carolina, using the flow through dynamic chamber technique, were used to evaluate the Coupled Mass Transfer and Chemical Reactions model and Equilibrium model. Sensitivity analysis shows that ammonia flux increases exponentially with lagoon temperature and pH, but a linear increase was observed with an increase in total ammoniacal nitrogen (TAN). Ammonia flux also shows a nonlinear increase with increasing wind speed. Observed ammonia fluxes were generally lower in the cold season than in the warm season when lagoon temperatures are higher. About 41% of the Equilibrium model predictions and 43% of the Coupled model predictions are found to be within a factor of two of the observed fluxes. Several model performance statistics were used to evaluate the performance of the two models against the observed flux data. These indicate that the simpler Equilibrium model does as well as the Coupled model. The possible effects of the “artificial” environment within the chamber, which is different from that in the ambient atmospheric conditions above the open lagoon surface, on the measured fluxes are also recognized. Actual layout of barns and lagoons on the farms was used to simulate dry deposition downwind of the farm. Dry deposition velocity, dispersion and dry deposition of ammonia were studied over different seasons and under different stability conditions. Dry deposition velocities were underpredicted by AERMOD when compared with observed dry deposition velocities. Dry deposition velocities were the highest under near neutral conditions and lowest under stable conditions. The highest deposition at short range occurs under nighttime stable conditions and the lowest deposition occurs during daytime unstable conditions. Significant differences in model predicted depositions over crop and grass surfaces are found under stable conditions. Wind orientation at the farm can also affect deposition of ammonia downwind of the farm.