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Abstract Measurements of atmospheric ammonia (NH₃) concentrations and fluxes are limited in coastal regions in the eastern U.S. In this study, continuous and high temporal resolution measurements (5s) of atmospheric NH₃concentrations were recorded using a cavity ring‐down spectrometer in a temperate tidal salt marsh at the St Jones Reserve (Dover, DE). Micrometeorological variables were measured using an eddy covariance system which is part of the AmeriFlux network (US‐StJ). Soil, plant, and water chemistry were also analyzed to characterize the sources and sinks of atmospheric NH₃. A new analytical methodology was used to estimate the average ecosystem‐scale diurnal cycle of NH₃fluxes by replicating the characteristics of a chamber experiment. This virtual chamber approach estimates positive surface fluxes in continuing strongly stable conditions when mixing with the air above is minimal. Our findings show that tidal water level may have a significant impact on NH₃emissions from the marsh. The largest fluxes were observed at low tide when more soil was exposed. While it is expected that NH₃fluxes will peak when the air temperature maximizes, high tide occurred concurrently with midday peaks in solar irradiance led to a decrease in NH₃fluxes. Furthermore, soil, plant, and water chemistry measurements underpinning the NH₃concentrations and fluxes lead us to conclude that this coastal wetland ecosystem can act as either a sink or a source of NH₃. Such measurements provide novel data on which we can base reliable parameterizations to simulate NH₃emissions from coastal salt marsh ecosystems using surface‐atmosphere transfer models.