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

Abstract

Atmospheric ammonia ( NH 3 ) measurements are needed to better understand the impacts of NH 3 emissions on aerosol formation and concentrations and anthropogenic changes to the N cycle. This paper describes concentration measurements of NH 3 using differential optical absorption spectroscopy (DOAS), tracer ratio flux experiments, and development of a NH 3 emissions model from a dairy milking cow free stall house with concrete floors. An area source tracer gas ratio method was used to determine NH 3 fluxes which involved releasing SF 6 as the tracer gas from the upwind edge of the stalls and measuring the tracer concentration downwind along with the DOAS NH 3 measurements. The flux is calculated from the ratio of the NH 3 and SF 6 concentrations and the SF 6 release rate and taking into account the differences in area and dispersion. The measured stall flux for the summers averaged 29 ± 19 g NH 3 cow - 1 h - 1 at an average temperature of 18 ± 5 ∘ C . The emissions model calculated liquid NH 3 concentrations in urine puddles, NH 3 volatilization, theoretical and empirical mass transfer to the bulk atmosphere, and NH 3 transport. The predicted concentrations were within ± 30 % using an empirical mass transfer coefficient and within ± 41 % using a theoretical mass transfer coefficient. Total annual NH 3 emissions for the dairy of 185 milking cows was 7400 kg or 40 kg NH 3 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.