This study examines NH₃ emissions from UK agriculture and the role it plays in PM_2.5 formation, focusing on the dairy, pig, and poultry sectors. Using regional and local air quality models, we find that a 13 % NH₃ reduction cuts PM_2.5 by only ~1 % due to NH₃-rich air. The regional model may underestimate PM_2.5, while the local modelling shows that emissions disperse within 700 m. The study highlights the value of combining models to better understand the spread of pollutants and to improve PM_2.5 control strategies.