Predicting Indoor Ammonia Concentration and House-Level Emissions via Dynamic Modelling of Slurry-to-Exhaust Transfer in a Finishing Pig House

Ammonia (NH3) from pig houses contributes to air-quality degradation and odor, yet farm-level emissions are highly sensitive to housing design, slurry chemistry and management. This study developed and validated a minute-resolution dynamic model for indoor NH3 concentration and house-level emission in a mechanically ventilated finishing pig house. Volatilization from the slurry surface was computed from total ammonia nitrogen (TAN), pH and temperature using established mass-transfer formulations, and coupled between two zones (pit headspace and room airspace) via advection and diffusion across the slatted-floor open area. Over one production cycle, key drivers and indoor NH3 were monitored; discrete TAN observations were upsampled to minute resolution by linear interpolation. Model coefficients were optimized by a genetic algorithm with chronological 70/30 splits for calibration and validation in the grower and finisher phases, respectively. The calibrated model reproduced minute-scale dynamics (validation RMSE 1.53–1.76 ppm, R2 0.87–0.88; MAPE 9.95–10.87%). Sobol’s global sensitivity analysis identified ventilation rate as the dominant driver of indoor concentration, and TAN and slurry pH as the principal drivers of emissions. The model provides decision support for minute-scale monitoring and management, and can be integrated with factor-control methods and ICT-based supervisory systems.