Effect of storage and field acidification on emissions of NH3, NMVOC, and odour from field applied slurry in winter conditions.

Land spreading of liquid animal manure (slurry) is a major source of atmospheric emissions. Ammonia (NH3) emission is of concern, as it is one of the main contributors to ambient air pollution and nitrogen deposition. Storage and field acidification of the slurry prior to application is used to mitigate NH3 emission, but the effect of acidification on emissions of odorous non-methane volatile organic compounds (NMVOC) has not been investigated, and there is a scarcity of data investigating the effect of field acidification. Four field experiments, two with cattle slurry and two with pig slurry, were performed. Ammonia and NMVOC emissions were measured simultaneously in a system of dynamic chambers and online measurements by cavity ring-down spectroscopy (CRDS) and proton-transfer-reaction mass spectrometry (PTR-MS). The system allowed for a high time resolution and low variation. All four experiments were performed under cold conditions (<10°C average temperature). Storage and field acidification significantly lowered the NH3 emission by 79 ± 18% and 30 ± 6% on average, respectively. The NMVOC cumulative emission increased by 202 ± 133% and 17 ± 16% on average after storage and field acidification, respectively, even if the increase was only significant for storage acidification. Storage acidification significantly increased the emissions of odour at most measuring times. The increases of cumulative NMVOC emissions and odour was primarily caused by higher emissions of volatile fatty acids.