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 (NH3(g)) concentrations and assessing the effects of agricultural waste management practices on NH3(g) emissions. The Ogawa sampler, with filter-discs impregnated with citric acid, was used to trap and determine NH3(g) concentrations in a variety of agricultural settings. A wide range of NH3(g) concentrations can be monitored by varying the sampler exposure time, provided that no more than 10 μg of NH3-N are adsorbed on the acid-coated filters. Concentrations less than 1 μg NH3-N m−3 can be detected using long deployments ( 14 days), while concentrations as great as 10 mg NH3-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 NH3(g) were similar to those determined using dilute-acid gas scrubbers. Background levels of NH3(g) at a non-agricultural site in southern Delaware were typically <1 μg NH3-N m−3. The air entering a chicken house was 10 μg NH3-N m−3, reflecting the background levels in agricultural settings in this region. Within the house, concentrations 8.5 mg NH3-N m−3 were observed, reflecting the high rates of NH3(g) emission from chicken excreta. Using measured NH3(g) concentrations and poultry house ventilation rates, we estimate that each broiler grown to production size over 6 weeks contributes approximately 19±3 g of NH3-N to the atmosphere, a value consistent with other published results.