Method: A standardised laboratory method for measuring ammonia volatilisation from pig slurry using a dynamic flux multichamber system

Ammonia ( NH 3 ) emissions generated by animal manure represent a challenge for the current livestock system, especially in the context of pig production. Standardised methods for measuring NH 3 concentration in pig slurry are needed to assess whether specific management strategies (e.g. low-protein diets and feed additives) can reduce NH 3 emissions. Therefore, the aim of this study was to provide a standardised procedure and test the repeatability in measuring NH 3 concentration in pig slurry using a laboratory-controlled method based on a dynamic flux multichamber system. Five slurry mixes of 348 g each were prepared using spot faecal and urine samples from a single pig. Every mix was composed of 87 g of faeces, 87 g of urine, and 174 g of distilled water. For each mix, three replicates of 100 g were realised, for a total of 15 slurry replicates of five slurry mixes. The 15 slurry replicates were contained in jars, placed in a water bath (21 °C), and injected with an even flow of synthetic air (approx. 0.3 L/min). The replicates were connected to a cavity ring-down spectrometer ( CRDS ), which, combined with a multichannel sampler, measured the NH 3 concentration of the outgoing air flow from the slurry replicates for 168.75 consecutive hours. Each slurry replicate was measured cyclically for 15 min, with a 10-min interval between two slurry replicates over 168.75 h of measurements. The values recorded during the final 60 s of each 15-min period were interpolated on an hourly basis, obtaining one NH 3 concentration value per hour. To test the repeatability of the method, CVs of area under the curve for NH 3 concentration ( AUC NH 3 , ppm × h), NH 3 concentration peak value ( PV NH 3 , ppm) and time to reach the peak ( TTP , h) were calculated within pairs of replicates from the same mix and within pairs of mixes. For the slurry mixes, all the CVs calculated showed a variation lower than 10%. Among the replicates, only the CV related to the TTP registered a value higher than 10% for four pairs of replicates out of 15. These findings suggest that the proposed dynamic flux multichamber system provides a standardised and repeatable approach for measuring NH 3 concentration in pig slurry under controlled laboratory conditions.