Inverse-Dispersion Calculation of Ammonia Emissions from Wisconsin Dairy Farms

Abstract

Ammonia (NH3) emissions were determined from three commercial dairy farms in the north-central U.S. The dairies employed similar management, having naturally ventilated free-stall barns where barn waste is scraped and transferred to outdoor lagoons. Three potential emission sources were distinguished at each farm: barns, lagoons, and sand separators. A backward Lagrangian stochastic (bLS) inverse-dispersion technique was used to measure emissions. Total farm emission varied from 15 to 330 kg NH3 d-1 depending on the farm and season. Inter-farm variability was largely explained by farm size (animal population). Emissions showed variability on seasonal and daily scales: summer rates were roughly ten times those of the winter, and mid-day rates were approximately three times those at night. The lagoons emitted 37% to 63% of the farm total during summer and fall, but they were frozen in winter and their emissions were immeasurably small. The yearly per-animal emissions from the three dairies were estimated at 20, 19, and 20 kg NH3 animal-1 year-1. Regarding the measurement technique, bLS proved well-suited to our study. With modest resources we were able to measure emissions from the variety of sources at each farm and quickly move between farms. Overall agreement in measured emissions at the three farms, together with a general harmony of our measurements with those from previous studies, provides a measure of confidence in the measurement strategy.