Data comprise monthly ammonia air concentrations from UK CEH ALPHA® (Adapted Low-cost Passive High Absorption) samplers co-located with UKEAP DELTA sites. The UK Eutrophying and Acidifying atmospheric Pollutants (UKEAP) network measures air pollutants at rural sites across the UK. The UK CEH ALPHA® sampler is a passive sampler for measuring NH3 in air. Originally the purpose of these measurements was for a calibrated ALPHA® uptake rate for the UK CEH Edinburgh research laboratory. Local site operator duties are completed by UK CEH staff and AFBI staff (at Hillsborough) and analysis is completed by UK Centre for Ecology and Hydrology Edinburgh. The sites were set up on 1st March 2020 and measurements are ongoing. Full details about this dataset can be found at https://doi.org/10.5285/1766eb32-1878-47e6-8dc8-d434957d1e32