Abstract
Ground-level concentrations of NH
3 and NH
4
+ have been measured at 19 sites within a 35-km radius of Colchester, U.K., over a period of 17 months. Spatial variations in NH
3 are related to local sources, with livestock farming causing pronounced elevations in concentration in the locality. Seasonal variations are evident, with highest concentrations in the hotter months of the year. Concentrations of NH
4
+ are far more spatially uniform, consistent with its formation during atmospheric transport and relative atmospheric persistence.