A methodology for the measurement of distributed agricultural sources of ammonia outdoors—Part 1: validation in a controlled environment

A flux frame method using recurved passive ammonia flux (PAF) samplers for the measurement of distributed outdoor agricultural sources of ammonia (NH3) was evaluated in a controlled environment. The collection efficiency of the samplers was determined in a wind tunnel at controlled values of NH3 flux density (0.77–13.5 mg NH3 m−2 s−1), and over a range of angles of orientation to the flow direction (0°, 30°, 60°, 70°, 80° and 90°). The samplers were effective up to a wind speed of 7 m s−1 and an angle of 80° with a mean collection efficiency of 71%. The flux frame method had a mean collection efficiency of 87.4% when used with ground level point sources under controlled conditions in an open-circuit wind tunnel with boundary layer airflow characteristics.