Seasonal and Spatial Distribution of Ambient Ammonia Concentrations Measured at a Large Open-Lot Dairy

The volatilization of NH3 from dairy production facilities is not only a loss of valuable N, but also an air quality concern because NH3 plays a role in the formation of airborne particulate matter, which can be a health hazard. The ambient NH3 concentrations over several seasons at 3 locations (open lots, compost yard, lagoon) throughout a large open-lot dairy were determined, as well as the spatial distribution of NH3 over the open-lot area. There was a significant main effect of location (P < 0.0001), which followed the trend of lot > lagoon = compost > background, with averages of 0.58, 0.33, 0.30, and 0.04 mg NH3/m3, respectively. The effect of weather and lot conditions on the spatial distribution of NH3 across the lots was evident, with lower concentrations and less spatial variability in winter months when the lots were frozen compared with wetter warmer months. Lower NH3 concentrations and less spatial variability were also measured when manure stockpiles were removed from the open lots and the lots were dry. Significantly greater NH3 concentrations were generated in the lot area versus the compost and lagoon areas, which were not significantly different. Because the lots are greater in size by a factor of approximately 6, it is evident that NH3 emissions from this sector of the dairy contribute the greatest amount of NH3 to the atmosphere.