Capture efficiency of four chamber designs for measuring ammonia emissions

Ammonia (NH₃) emissions are an economically and environmentally significant loss pathway of fertilizer and soil-derived N. Chambers are a commonly used method to quantify NH₃ emissions in plot-scale agricultural research. Although this method is widely used, its accuracy may be influenced by the overall design of the chamber, its components, and its interaction with the environment. Four NH₃ chamber designs, including open, open + polytetrafluoroethylene (PTFE), semi-open, and closed, were deployed over a dilute NH₃ solution for 6 h on four dates to determine the effect of chamber design on NH₃ capture efficiency. The solution volume and concentration were measured before and after acid trap deployment, and total volatile NH₃ emission was assumed to be equal to the mass N loss. The NH₃ capture efficiency relative to the estimated total emissions was greatest for the open design (12.9%), whereas the semi-open chamber was the least efficient (3.5%). The closed chamber reduced NH₃ emissions relative to the open and semi-open designs by inhibiting convective gas transport beneath the chamber footprint.