Validation of Ogawa passive samplers for the determination of gaseous ammonia concentrations in agricultural settings

The Ogawa passive sampler (Ogawa USA, Pompano Beach, Florida) is a useful tool for monitoring atmospheric ammonia (NH 3(g)) concentrations and assessing the effects of agricultural waste management practices on NH 3(g) emissions. The Ogawa sampler, with filter-discs impregnated with citric acid, was used to trap and determine NH 3(g) concentrations in a variety of agricultural settings. A wide range of NH 3(g) concentrations can be monitored by varying the sampler exposure time, provided that no more than ∼10 μg of NH 3-N are adsorbed on the acid-coated filters. Concentrations less than 1 μg NH 3-N m −3 can be detected using long deployments (⩽14 days), while concentrations as great as 10 mg NH 3-N m −3 may be determined in very short (e.g. 5 min) deployments. Reproducibility ranged from 5% to 10% over the range of concentrations studied and passive determinations of NH 3(g) were similar to those determined using dilute-acid gas scrubbers. Background levels of NH 3(g) at a non-agricultural site in southern Delaware were typically