Design of the internal geometry of a passive flux sampler and calibration for quantification of ammonia emissions

Passive flux samplers (PFS) have gained widespread adoption for quantifying ammonia (NH3) emissions owing to their operational simplicity and cost-effectiveness, but their performance can be limited by sorption capacity and incomplete collection. This study introduces a novel NH3-PFS incorporating a 3D-printed internal structure that enables a dual layer of microfiber glass filter configuration. Two additive manufacturing geometries, ring and helix, were evaluated through aerodynamic and sorption calibration. Both designs preserved a strong linear relationship between external and internal airflow, yielding conventional k-factors of 0.54 for the ring and 0.59 for the helix. The helix geometry substantially increased sorption capacity, achieving an initial NH3 collection efficiency of 100% and increasing sorption capacity before breakthrough to 1115 µg, compared with 465 µg for the ring design. The PFS incorporating the helix geometry exhibited a mean recovery efficiency of 90% and consistent aerodynamic performance across the tested wind-speed and wind-direction ranges. Temperature had a limited effect on NH3 collection, whereas increasing relative humidity did not deteriorate PFS performance under the tested range representative of agricultural environments, including fertilization, manure management, and animal housing. These results demonstrate that additive manufacturing can facilitate the integration of customized and repeatable internal geometries that improve sorption performance while preserving the linear aerodynamic response required for PFS operation. The resulting design increases sampling capacity and reliability, enables longer deployment periods under elevated NH3 concentrations, and supports more robust determination of agricultural NH3 emissions.