Measurement and modeling of atmospheric flux of ammonia from dairy milking cow housing

Atmospheric ammonia (NH3) measurements are needed to better understand the impacts of NH3 emissions on aerosol formation and concentrations and anthropogenic changes to the N cycle. This paper describes concentration measurements of NH3 using differential optical absorption spectroscopy (DOAS), tracer ratio flux experiments, and development of a NH3 emissions model from a dairy milking cow free stall house with concrete floors. An area source tracer gas ratio method was used to determine NH3 fluxes which involved releasing SF6 as the tracer gas from the upwind edge of the stalls and measuring the tracer concentration downwind along with the DOAS NH3 measurements. The flux is calculated from the ratio of the NH3 and SF6 concentrations and the SF6 release rate and taking into account the differences in area and dispersion. The measured stall flux for the summers averaged 29 +/- 19 g NH3 cow(-1) h(-1) at an average temperature of 18 +/- 5 degrees C. The emissions model calculated liquid NH3 concentrations in urine puddles, NH3 volatilization, theoretical and empirical mass transfer to the bulk atmosphere, and NH3 transport. The predicted concentrations were within +/- 30% using an empirical mass transfer coefficient and within 41% using a theoretical mass transfer coefficient. Total annual NH3 emissions for the dairy of 185 milking cows was 7406 kg or 40 kg NH3 cow(-1)year(-1), estimated total N excretions are 180 kg cow(-1)year(-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. (c) 2007 Elsevier Ltd. All rights reserved.