Field-scale ammonia flux measurements at an agricultural field in southern Finland by mass spectrometry and eddy covariance

• Mass spectrometry based eddy covariance quantifying NH 3 emission. • NH 3 emissions up to 1.4 μgN m -2 s -1 during application of solid fraction of manure. • Only ∼2.25 % of loss of TAN as NH 3 . Ammonia (NH 3 ) fluxes were measured at a research farm in Southern Finland from 16 March to 22 May 2023 using the eddy covariance technique with a benzene chemical ionization mass spectrometer. NH 3 emissions (0-0.02 µgN m -2 s -1 ) remained low for the primarily studied field until its fertilization with the solid fraction from solid-liquid separation of cattle manure on 27 April, which led to fluxes up to 1.4 µgN m -2 s -1 . The manure was incorporated into the soil by harrowing the next day, after which the fluxes declined rapidly and remained below 0.1 µgN m -2 s -1 . The NH 3 emission factor (EF) from the solid fraction was 2.25% of applied total ammoniacal nitrogen (TAN) for the whole campaign, with 85% of the emissions during 27 April to 22 May occurring within 30 h. This EF lies at the low end of wide range of values reported for unincorporated solid cattle manure in literature (2.5–70%) depending on manure type and management. The comparatively low emissions in this study likely reflect the characteristics of the separated solid fraction and rapid post-application incorporation. Long-term background NH 3 concentrations and fluxes were generally low and broadly linearly dependent on temperature, while no clear dependence on windspeed was observed. The measured background concentrations (0.3±0.2 µg m -3 ) were similar to as reported for a nearby urban-background site in Finland (0.2±0.3 µg m -3 ) but much lower than values observed at agricultural hotspots in Europe (>10 µg m -3 ).