Measuring and Modeling Atmospheric Ammonia from Agricultural Sources at a Landscape Scale

Measurements of atmospheric ammonia (NH₃) concentrations were made at 28 sites on a landscape scale in Bretagne (north-western France) using passive diffusion ALPHA (adapted low-cost passive high adsorption) samplers. The measured ambient concentrations of NH₃ vary typically between 2.03 and 105.17 NH₃ μg/m³ within a few 100 m (∼700 m) from the emission sources. The interpretation of measurements was supported by simulations with the AERMOD model using a horizontal fine spatial resolution of 25 × 25 m². Simulations were based on estimates of the NH₃ emission calculated separately from livestock grazing, livestock housing, waste storage, land spreading, and mineral fertilizers in the area during the four seasons of 2008. Our findings show that AERMOD performance is acceptable for this experimental study with intensive livestock farming. However, the model still overestimates the observed NH₃ concentrations over most of the area, which is well marked for cold seasons and low wind speeds; this overestimation could be more attributed to an overestimation of NH₃ emissions in the model, source placements, passive sampler placements, and depletion/deposition processes, rather than roughness length and source height estimates.