Measurements and modeling of atmospheric flux of ammonia from an anaerobic dairy waste lagoon

Abstract

Atmospheric anthropogenic ammonia ( NH 3 ) 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 DOAS NH 3 measurement. The flux is calculated by ratioing the tracer flux and concentration with the NH 3 concentration and taking into account the differences in area and dispersion over the area source. Measured fluxes from the tracer experiments ranged from 0.11 g m - 2 h - 1 at an air temperature of 11 ∘ C to 0.54 g m - 2 h - 1 at an air temperature of 27 ∘ C . The NH 3 emission models were based upon the temperature-dependent biological activity, the partitioning of NH 3 and NH 4 + in solution, and the partitioning of NH 3 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 were 55 kg NH 3 cow - 1 yr - 1 from all lagoons, estimated excretion is 180 kg N cow - 1 yr - 1 . Using literature lagoon design criteria to estimate lagoon size resulted in an underestimation of emissions of - 29 % .