Ammonia emissions from an uncovered dairy slurry storage tank over two years: Interactions with tank operations and meteorological conditions

The storage of slurry substantially contributes to the ammonia (NH3) released from livestock production. This study quantified farm-scale NH3 emissions from a circular open tank storing dairy cow slurry by means of continuous measurements over two years. Emissions were determined by scaling the product of line-integrated concentration measurements across the tank and wind speed measurements at 10 m height. The resulting data were calibrated to emissions determined using the integrated horizontal flux method. The data analysis was structured according to the main influencing factors: natural crust and meteorological conditions. The average annual emission was 0.065 g NH3 m−2 h−1 with a maximum of 1.67 g NH3 m−2 h−1. Annual emissions scaled to total ammoniacal nitrogen (TAN) were 3.3% of the TAN flow into the store. A natural crust on the slurry surface, which was strongly affected by agitation of the tank, diminished the gas release. An increasing time span after agitation led to correspondingly lower emissions. A greater filling level enhanced crust formation and induced an additional drop in emissions. Precipitation reduced emissions by 64%–86% compared to dry weather conditions. Higher wind speed and temperatures increased emissions. The emissions were highest in periods with weak or no crusting of the slurry surface, which covered 40% of the study time, but produced 61% of total emissions. The response of NH3 emissions to the interactions of influencing factors, which might vary considerably between stores, suggests that these factors require consideration for the determination of emission factors used for inventory reporting.