The tracer gas ratio method, using CO₂ as natural tracer, has been suggested as a pragmatic option to measure emissions from naturally ventilated (NV) barns without the need to directly estimate the ventilation rate. The aim of this research was to assess the performance of a low-cost Non-Dispersive Infra-Red (NDIR) sensor for intensive spatial field monitoring of CO₂ concentrations in a NV dairy cow house. This was achieved by comparing NDIR sensors with two commonly applied methods, a Photo-Acoustic Spectroscope (PAS) Gas Monitor and an Open-Path laser (OP-laser). First, calibrations for the NDIR sensors were obtained in the laboratory. Then, the NDIR sensors were placed in a dairy cow barn for comparison with the PAS and OP-laser methods. The main conclusions were: (a) in order to represent the overall barn CO₂ concentration of the dairy cow barn, the number of NDIR sensors to be accounted for average concentration calculation was dependent on barn length and on barn area occupation; and (b) the NDIR CO₂ sensors are suitable for multi-point monitoring of CO₂ concentrations in NV livestock barns, being a feasible alternative for the PAS and the OP-laser methods to monitor single-point or averaged spatial CO₂ concentrations in livestock barns.

Given the current scarcity of empirical data on ammonia (NH3) emissions from dairy cattle under different management-based mitigation techniques, a modeling approach to assess potential NH3 emission reduction factors is needed. This paper introduces a process-based model that estimates NH3 emission reduction factors for a dairy cattle barn featuring single or multiple management-based NH3 emission mitigation techniques, as compared to another barn, to which no mitigation measure is applied. The model accounts for the following emission mitigation measures: (a) floor scraping, (b) floor type, (c) floor flushing with water and (d) indoor acidification of manure. Model sensitivity analysis indicated that manure acidification was the most efficient NH3 emission reduction technique. A fair agreement was observed between reduction factors from the model and empirical estimates found in the literature. We propose a list of combinations of techniques that achieve the largest reductions. In order of efficiency, they are: (a) floor scraping combined with manure acidification (reduction efficiency 44-49%); (b) solid floor combined with scraping and flushing (reduction efficiency 21-27%); (c) floor scraping combined with flushing and (d) floor scraping alone (reduction efficiency 17-22%). The model is currently being used to advise the Flemish Government (Belgium), on the performance of certain NH3 emission reduction systems for dairy barns in Flanders.

SUMMARY. A laboratory-scale study was conducted to determine the effect of feeding laying hens a standard commercial diet supplemented with different dosages o