Atmospheric flux of ammonia from sprinkler application of dairy waste

Atmospheric ammonia (NH3)(NH3) emissions are a growing environmental and human health concern in the U.S. This paper describes an experiment to measure NH3NH3 emissions from the sprinkler application of dairy slurry to a grass field. The slurry was from milking cows that are housed in a freestall barn that is scraped daily and the waste is stored in a series of anaerobic lagoons that are emptied annually. Atmospheric measurements of NH3NH3 were made using differential optical absorption spectroscopy (DOAS) and tracer ratio flux experiments were used to determine field fluxes after application. An area source tracer ratio method was used to determine NH3NH3 field fluxes, it involved releasing SF6SF6 as the tracer gas from the upwind edge of the applied slurry and measuring the tracer concentration downwind along with the DOAS NH3NH3 measurements. The flux is calculated from the ratio of the NH3NH3 and SF6SF6 concentrations and the SF6SF6 release rate and taking into account the differences in area and dispersion. An emissions model was also developed for NH3NH3 volatilization after application based upon tracer flux data and modeling of the concentration data. Of the total ammonical nitrogen entering from the sprinkler pump, 18% volatilized before reaching the ground. The initial flux during the tracer experiment was 47μgm-2s-1 and this decreased to 17μgm-2s-1 during the experiment. Ambient measurements showed an exponential decay with time. An empirical exponential equation was fit to the measurement data and it had a mean bias of -0.10ppbv and a normalized mean bias of -0.050%-0.050%. A theoretical model had a mean bias of -11ppbv and a normalized mean bias of -5.5%-5.5%. Overall sprinkler waste application emissions for the 175 milking cows was 5900 kg NH3yr-1 or 34 kg NH3cow-1yr-1.