Estimation of NH₃ emissions from a naturally ventilated livestock farm using local-scale atmospheric dispersion modelling

Abstract. Agricultural livestock represents the main source of ammonia (NH₃) in Europe. In recent years, reduction policies have been applied to reduce NH₃ emissions. In order to estimate the impacts of these policies, robust estimates of the emissions from the main sources, i.e. livestock farms are needed. In this paper, the NH₃ emissions were estimated from a naturally ventilated livestock farm in Braunschweig, Germany during a joint field experiment of the GRAMINAE European project. An inference method was used with a Gaussian-3D plume model and with the Huang 3-D model. NH₃ concentrations downwind of the source were used together with micrometeorological data to estimate the source strength over time. Mobile NH₃ concentration measurements provided information on the spatial distribution of source strength. The estimated emission strength ranged between 6.4±0.18 kg NH₃ d⁻¹ (Huang 3-D model) and 9.2±0.7 kg NH₃ d⁻¹ (Gaussian-3D model). These estimates were 94% and 63% of what was obtained using emission factors from the German national inventory (9.6 kg d⁻¹ NH₃). The effect of deposition was evaluated with the FIDES-2D model. This increased the emission estimate to 11.7 kg NH₃ d⁻¹, showing that deposition can explain the observed difference. The daily pattern of the source was correlated with net radiation and with the temperature inside the animal houses. The daily pattern resulted from a combination of a temperature effect on the source concentration together with an effect of variations in free and forced convection of the building ventilation rate. Further development of the plume technique is especially relevant for naturally ventilated farms, since the variable ventilation rate makes other emission measurements difficult.